Pub Date : 2025-02-11DOI: 10.1016/j.jmmm.2025.172849
Andreas Lyberatos
A method of calculating exactly the switching time of the magnetization of a uniaxially anisotropic single domain (SD) particle at the boundary between thermo-activated and damping-limited reversal is presented. The generalized free energy function of the system is used to deduce the intrinsic switching field marking the transition point and numerical integration of the stochastic Landau–Lifshitz–Gilbert (LLG) equation of motion is carried out to determine the switching statistics. We study the variation of with the tilt angle of the applied field with respect to the easy axis, the grain size and damping. At the cross-over transition the barrierless reversal is driven by thermal perturbations and the switching time in the presence of an axial field varies as , where is the first order anisotropy constant and is the volume of the particle.
{"title":"On the transition between thermally activated and dynamic magnetic reversal of fine particles","authors":"Andreas Lyberatos","doi":"10.1016/j.jmmm.2025.172849","DOIUrl":"10.1016/j.jmmm.2025.172849","url":null,"abstract":"<div><div>A method of calculating exactly the switching time <span><math><msub><mrow><mi>t</mi></mrow><mrow><mi>o</mi></mrow></msub></math></span> of the magnetization of a uniaxially anisotropic single domain (SD) particle at the boundary between thermo-activated and damping-limited reversal is presented. The generalized free energy function of the system is used to deduce the intrinsic switching field marking the transition point and numerical integration of the stochastic Landau–Lifshitz–Gilbert (LLG) equation of motion is carried out to determine the switching statistics. We study the variation of <span><math><msub><mrow><mi>t</mi></mrow><mrow><mi>o</mi></mrow></msub></math></span> with the tilt angle of the applied field with respect to the easy axis, the grain size and damping. At the cross-over transition the barrierless reversal is driven by thermal perturbations and the switching time in the presence of an axial field varies as <span><math><mrow><msub><mrow><mi>t</mi></mrow><mrow><mi>o</mi></mrow></msub><mo>∝</mo><msqrt><mrow><msub><mrow><mi>K</mi></mrow><mrow><mi>u</mi></mrow></msub><mi>V</mi><mo>/</mo><msub><mrow><mi>k</mi></mrow><mrow><mi>B</mi></mrow></msub><mi>T</mi></mrow></msqrt></mrow></math></span>, where <span><math><msub><mrow><mi>K</mi></mrow><mrow><mi>u</mi></mrow></msub></math></span> is the first order anisotropy constant and <span><math><mi>V</mi></math></span> is the volume of the particle.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"617 ","pages":"Article 172849"},"PeriodicalIF":2.5,"publicationDate":"2025-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143386644","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-10DOI: 10.1016/j.jmmm.2025.172850
Noboru Yoshikawa, Masaya Goto
In this study, the effect of the Hext. variation rate (dHext./dt, t: time) on the temperature variation was investigated by applying tens of watts of microwave power at 5.8 GHz with the imposition of an external magnetic field (Hext.). A substantial temperature increase in ferromagnetic materials was observed under ferromagnetic resonance (FMR) conditions. The external magnetic field causing the temperature peak (HTpeak) was almost explained by the resonant magnetic field, considering the effect of the demagnetization field.
In the permalloy foils, the HTpeak was almost constant with respect to dHext./dt. In the Fe foil and the Fe3O4 particles, the HTpeak increased with dHext./dt during the increasing field sweep runs of Hext., but the HTpeak did not change very much during the decreasing runs.
As for these reasons, the saturation states of magnetization are taken into consideration. FMR could occur under conditions of unsaturated magnetization during increasing field sweep runs of Hext., resulting in a lower HTpeak, due to the lower demagnetization field. However, during the decreasing runs of Hext., the magnetization was saturated once or the specimen experienced the highest magnetization, which then resulted in a fixed HTpeak.
In the YIG particles, the effect of the Hext. variation rate on the HTpeak was small in both increasing and decreasing field sweep runs of Hext., because of the smaller magnetization compared to the others. It was also pointed out that macroscopic heat transfer processes need to be taken into consideration in order to interpret the observed HTpeak and the peak temperature.
{"title":"Temperature variation by FMR under high power microwave irradiation and effect of external magnetic field change rate","authors":"Noboru Yoshikawa, Masaya Goto","doi":"10.1016/j.jmmm.2025.172850","DOIUrl":"10.1016/j.jmmm.2025.172850","url":null,"abstract":"<div><div>In this study, the effect of the <em>H</em><sup>ext.</sup> variation rate (<em>dH<sup>ext</sup></em><sup>.</sup>/d<em>t</em>, <em>t</em>: time) on the temperature variation was investigated by applying tens of watts of microwave power at 5.8 GHz with the imposition of an external magnetic field (<em>H</em><sup>ext.</sup>). A substantial temperature increase in ferromagnetic materials was observed under ferromagnetic resonance (FMR) conditions. The external magnetic field causing the temperature peak (<em>H</em><sup>Tpeak</sup>) was almost explained by the resonant magnetic field, considering the effect of the demagnetization field.</div><div>In the permalloy foils, the <em>H</em><sup>Tpeak</sup> was almost constant with respect to <em>dH<sup>ext</sup></em><sup>.</sup>/d<em>t</em>. In the Fe foil and the Fe<sub>3</sub>O<sub>4</sub> particles, the <em>H</em><sup>Tpeak</sup> increased with <em>dH<sup>ext</sup></em><sup>.</sup>/d<em>t</em> during the increasing field sweep runs of <em>H</em><sup>ext.</sup>, but the <em>H</em><sup>Tpeak</sup> did not change very much during the decreasing runs.</div><div>As for these reasons, the saturation states of magnetization are taken into consideration. FMR could occur under conditions of unsaturated magnetization during increasing field sweep runs of <em>H</em><sup>ext.</sup>, resulting in a lower <em>H</em><sup>Tpeak</sup>, due to the lower demagnetization field. However, during the decreasing runs of <em>H</em><sup>ext.</sup>, the magnetization was saturated once or the specimen experienced the highest magnetization, which then resulted in a fixed <em>H</em><sup>Tpeak</sup>.</div><div>In the YIG particles, the effect of the <em>H</em><sup>ext.</sup> variation rate on the <em>H</em><sup>Tpeak</sup> was small in both increasing and decreasing field sweep runs of <em>H</em><sup>ext.</sup>, because of the smaller magnetization compared to the others. It was also pointed out that macroscopic heat transfer processes need to be taken into consideration in order to interpret the observed <em>H</em><sup>Tpeak</sup> and the peak temperature.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"618 ","pages":"Article 172850"},"PeriodicalIF":2.5,"publicationDate":"2025-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143419335","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-09DOI: 10.1016/j.jmmm.2025.172854
Bin Yang , Zhifeng Liu , Rui Feng , Wenlong Li
Magnetic memory detection technology has a distinct advantage in early detection of damage and stress concentration in ferromagnetic materials. It has attracted many scholars’ attention since it was proposed, but mainly focus on isolated defects, which is far from the real scenario. The damage formation of ferromagnetic material components in practical applications is random and uncertain, and defects often exist in the form of defect clusters of different shapes and sizes. The interaction between adjacent defects has a significant influence on the magnetic memory signals (MMS) and quantitative evaluation of defects in ferromagnetic materials. In this paper, the correlation between three-dimensional (3D) of MMS induced by double circular hole defects and defect spacing, defect size, as well as the applied loading were investigated by tensile tests. The Q355B structural steels were machined into specimens with double defects of 7 types of spacing and 5 types of diameter. Some magnetic parameters were extracted to characterize the distortion of MMS in the defect area. The effects of applied loading, defect spacing, and defect size on magnetic characteristic parameters were discussed. The research results indicate that the peak-valley values of the MMS of double defects increase with the increase of load, and the wave spacing values are not influenced by the applied loading. Besides, the interaction between adjacent defects decreases with the increase of defect spacing when the size of two adjacent defects keeps constant. However, when the distance between adjacent defects L ≥ 10 mm, the interaction is disappeared, and the two defects can be regarded as isolated hole defects. The interaction between adjacent defects increases with the increase of defect size on the right when the defect spacing keeps constant. In addition, there is a good correspondence between the gradient of the MMS and the equivalent stress along the loading direction. The vector locus synthesized by the X-directional and Z-directional components of the MMS is capable of characterizing the defect spacing, defect size, and applied loading. This study provides a theoretical basis and engineering value for accurately evaluating the size of defects in ferromagnetic materials by means of magnetic memory detection method.
{"title":"Magnetic memory signals induced by adjacent circular hole defects","authors":"Bin Yang , Zhifeng Liu , Rui Feng , Wenlong Li","doi":"10.1016/j.jmmm.2025.172854","DOIUrl":"10.1016/j.jmmm.2025.172854","url":null,"abstract":"<div><div>Magnetic memory detection technology has a distinct advantage in early detection of damage and stress concentration in ferromagnetic materials. It has attracted many scholars’ attention since it was proposed, but mainly focus on isolated defects, which is far from the real scenario. The damage formation of ferromagnetic material components in practical applications is random and uncertain, and defects often exist in the form of defect clusters of different shapes and sizes. The interaction between adjacent defects has a significant influence on the magnetic memory signals (MMS) and quantitative evaluation of defects in ferromagnetic materials. In this paper, the correlation between three-dimensional (3D) of MMS induced by double circular hole defects and defect spacing, defect size, as well as the applied loading were investigated by tensile tests. The Q355B structural steels were machined into specimens with double defects of 7 types of spacing and 5 types of diameter. Some magnetic parameters were extracted to characterize the distortion of MMS in the defect area. The effects of applied loading, defect spacing, and defect size on magnetic characteristic parameters were discussed. The research results indicate that the peak-valley values of the MMS of double defects increase with the increase of load, and the wave spacing values are not influenced by the applied loading. Besides, the interaction between adjacent defects decreases with the increase of defect spacing when the size of two adjacent defects keeps constant. However, when the distance between adjacent defects L ≥ 10 mm, the interaction is disappeared, and the two defects can be regarded as isolated hole defects. The interaction between adjacent defects increases with the increase of defect size on the right when the defect spacing keeps constant. In addition, there is a good correspondence between the gradient of the MMS and the equivalent stress along the loading direction. The vector locus synthesized by the X-directional and Z-directional components of the MMS is capable of characterizing the defect spacing, defect size, and applied loading. This study provides a theoretical basis and engineering value for accurately evaluating the size of defects in ferromagnetic materials by means of magnetic memory detection method.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"618 ","pages":"Article 172854"},"PeriodicalIF":2.5,"publicationDate":"2025-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143402785","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-08DOI: 10.1016/j.jmmm.2025.172840
Yanwen Hu , Tingzhen Heng , Tingrong Zhang , Wenying Zhou , Yaodong Ma
This paper proposes a comprehensive evaluation method of magnetic coupling resonance wireless power transfer (MCRWPT) system with a single-layer ferrite shielding structure. The method comprehensively considers the system’s efficiency, economy and safety, transfer efficiency, weight, and magnetic flux leakage. By constructing an objective function, encoding the ferrite region, the shielding structure is optimized using a genetic algorithm. The influence of different orders and construction methods of ferrite encoding arrays on the comprehensive optimization results of the system is studied. The research results indicate that the 6th-order rotational symmetry construction approach has better optimization performance than the 6th-order axisymmetric construction approach, the 8th-order rotational symmetry construction approach has better optimization performance than the 6th-order rotational symmetry construction approach. Compared with the ferrite full shielding structure, the number of ferrites used in the 8th-order rotational symmetric optimization structure has been reduced by 56.25 %. The experimental results show that the transfer efficiency of the MCRWPT system with an 8th-order ferrite shielding structure reaches 79.55 % at a transmission distance of 150 mm. The optimized shielding structure not only improves the overall performance of the MCRWPT system but also has high economic benefits.
{"title":"Optimization design of magnetic coupling resonance wireless power transfer system with single-layer ferrite shielding based on genetic algorithm","authors":"Yanwen Hu , Tingzhen Heng , Tingrong Zhang , Wenying Zhou , Yaodong Ma","doi":"10.1016/j.jmmm.2025.172840","DOIUrl":"10.1016/j.jmmm.2025.172840","url":null,"abstract":"<div><div>This paper proposes a comprehensive evaluation method of magnetic coupling resonance wireless power transfer (MCRWPT) system with a single-layer ferrite shielding structure. The method comprehensively considers the system’s efficiency, economy and safety, transfer efficiency, weight, and magnetic flux leakage. By constructing an objective function, encoding the ferrite region, the shielding structure is optimized using a genetic algorithm. The influence of different orders and construction methods of ferrite encoding arrays on the comprehensive optimization results of the system is studied. The research results indicate that the 6th-order rotational symmetry construction approach has better optimization performance than the 6th-order axisymmetric construction approach, the 8th-order rotational symmetry construction approach has better optimization performance than the 6th-order rotational symmetry construction approach. Compared with the ferrite full shielding structure, the number of ferrites used in the 8th-order rotational symmetric optimization structure has been reduced by 56.25 %. The experimental results show that the transfer efficiency of the MCRWPT system with an 8th-order ferrite shielding structure reaches 79.55 % at a transmission distance of 150 mm. The optimized shielding structure not only improves the overall performance of the MCRWPT system but also has high economic benefits.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"617 ","pages":"Article 172840"},"PeriodicalIF":2.5,"publicationDate":"2025-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143386642","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-08DOI: 10.1016/j.jmmm.2025.172846
Mustafa Özgür, Suat Pat, Şadan Korkmaz
<div><div>Nanosized ferromagnets hold great potential for the development of nanoscale spintronic devices. In this study, the structural, electronic and magnetic properties of FeO, Fe<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>, and Fe<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span> are investigated using density functional theory (DFT) calculations with and without Hubbard U correction. The inclusion of the Hubbard U term is crucial for accurately capturing the strong electron–electron correlations in iron oxides, which significantly affect their electronic and magnetic behaviors, including the Curie temperature. For FeO, the PBEsol calculations predict a metallic band structure, while the PBEsol+U calculations yield a band gap of 2.08 eV. Similarly, for Fe<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>, the band gap increases from 0.59 eV with PBEsol to 2.50 eV with PBEsol+U, and for Fe<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span>, it changes from metallic to 1.71 eV when the Hubbard U correction is applied. The magnetic moments for Fe atoms also show a significant improvement with the inclusion of the Hubbard U correction. In FeO, the magnetic moment increases from 3.21 <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mtext>B</mtext></mrow></msub></math></span> with PBEsol to 3.38 <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mtext>B</mtext></mrow></msub></math></span> with PBEsol+U. For Fe<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>, the values change from 3.15 <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mtext>B</mtext></mrow></msub></math></span> to 3.85 <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mtext>B</mtext></mrow></msub></math></span>, and for Fe<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span>, from 3.32 <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mtext>B</mtext></mrow></msub></math></span> to 3.75 <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mtext>B</mtext></mrow></msub></math></span>. These results bring the calculated values closer to the experimental observations. The Curie temperatures, calculated using magnetic exchange constants determined from the Green function method, also highlight the impact of the Hubbard U correction. For FeO, the Curie temperature dramatically decreases from 825 K with PBEsol to 330 K with PBEsol+U. In Fe<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math
{"title":"Hubbard U correction on magnetic interactions and Curie temperatures of FeO, Fe2O3, and Fe3O4","authors":"Mustafa Özgür, Suat Pat, Şadan Korkmaz","doi":"10.1016/j.jmmm.2025.172846","DOIUrl":"10.1016/j.jmmm.2025.172846","url":null,"abstract":"<div><div>Nanosized ferromagnets hold great potential for the development of nanoscale spintronic devices. In this study, the structural, electronic and magnetic properties of FeO, Fe<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>, and Fe<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span> are investigated using density functional theory (DFT) calculations with and without Hubbard U correction. The inclusion of the Hubbard U term is crucial for accurately capturing the strong electron–electron correlations in iron oxides, which significantly affect their electronic and magnetic behaviors, including the Curie temperature. For FeO, the PBEsol calculations predict a metallic band structure, while the PBEsol+U calculations yield a band gap of 2.08 eV. Similarly, for Fe<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>, the band gap increases from 0.59 eV with PBEsol to 2.50 eV with PBEsol+U, and for Fe<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span>, it changes from metallic to 1.71 eV when the Hubbard U correction is applied. The magnetic moments for Fe atoms also show a significant improvement with the inclusion of the Hubbard U correction. In FeO, the magnetic moment increases from 3.21 <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mtext>B</mtext></mrow></msub></math></span> with PBEsol to 3.38 <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mtext>B</mtext></mrow></msub></math></span> with PBEsol+U. For Fe<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>, the values change from 3.15 <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mtext>B</mtext></mrow></msub></math></span> to 3.85 <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mtext>B</mtext></mrow></msub></math></span>, and for Fe<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span>, from 3.32 <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mtext>B</mtext></mrow></msub></math></span> to 3.75 <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mtext>B</mtext></mrow></msub></math></span>. These results bring the calculated values closer to the experimental observations. The Curie temperatures, calculated using magnetic exchange constants determined from the Green function method, also highlight the impact of the Hubbard U correction. For FeO, the Curie temperature dramatically decreases from 825 K with PBEsol to 330 K with PBEsol+U. In Fe<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"617 ","pages":"Article 172846"},"PeriodicalIF":2.5,"publicationDate":"2025-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143376989","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A2Ni7 compounds (A = rare earth) are of interest for their fundamental structural and magnetic properties such as weak itinerant magnets when A = Y and La. In this study, the crystal structure and magnetic properties of La2−xA′xNi7 compounds with magnetic rare earth elements (A′ = Sm, Gd) have been investigated combining X-ray powder diffraction and magnetic measurements. These intergrowth compounds crystallize in a mixture of 2H hexagonal (Ce2Ni7-type) and 3R rhombohedral (Gd2Co7-type) polymorphic structures which are related to the stacking of [AB5] and [A2B4] subunits along the c-axis. The average cell volume decreases linearly versus A′ content, whereas the c/a ratio reaches a minimum at x = 1, due to geometric constraints upon A′ for La substitution between the two different subunits. The magnetic properties strongly depend on the structure type and the A′ content. Hexagonal La2Ni7 is a weak antiferromagnet (wAFM) at low field and temperature and undergoes metamagnetic transitions towards weak ferromagnetic state (wFM) under applied field. Under an applied field of 0.1 T, La2−xA′xNi7 intermetallic compounds display two different transition temperatures T1 and T2 that both increase with x. T1 is associated with a wFM-wAFM transition in the 2H phase for A′ = Sm, whereas T2 is related to the Curie temperature of both 2H and 3R phases. A metamagnetic behaviour is observed between T1 and T2 with transition field µ0HTrans between 2 and 3.5 T for compounds with A′ = Sm. The La2−xSmxNi7 compounds (x > 0) behave as hard magnets with a large coercive field µ0HC at low temperature (µ0HC > 9 T at 5 K for x = 2), whereas the La2−xGdxNi7 compounds (x > 0) are soft ferrimagnets with a linear increase of the saturation magnetization versus Gd content.
{"title":"Relationship between polymorphic structures and magnetic properties of La2−xA′xNi7 compounds (A′ = Sm, Gd)","authors":"Valérie Paul-Boncour , Véronique Charbonnier , Nicolas Madern , Lotfi Bessais , Judith Monnier , Junxian Zhang","doi":"10.1016/j.jmmm.2025.172859","DOIUrl":"10.1016/j.jmmm.2025.172859","url":null,"abstract":"<div><div><em>A</em><sub>2</sub>Ni<sub>7</sub> compounds (<em>A</em> = rare earth) are of interest for their fundamental structural and magnetic properties such as weak itinerant magnets when <em>A</em> = Y and La. In this study, the crystal structure and magnetic properties of La<sub>2−</sub><em><sub>x</sub>A</em>′<em><sub>x</sub></em>Ni<sub>7</sub> compounds with magnetic rare earth elements (<em>A</em>′ = Sm, Gd) have been investigated combining X-ray powder diffraction and magnetic measurements. These intergrowth compounds crystallize in a mixture of 2<em>H</em> hexagonal (Ce<sub>2</sub>Ni<sub>7</sub>-type) and 3<em>R</em> rhombohedral (Gd<sub>2</sub>Co<sub>7</sub>-type) polymorphic structures which are related to the stacking of [<em>AB</em><sub>5</sub>] and [<em>A</em><sub>2</sub><em>B</em><sub>4</sub>] subunits along the <em>c</em>-axis. The average cell volume decreases linearly versus <em>A</em>′ content, whereas the <em>c</em>/<em>a</em> ratio reaches a minimum at <em>x</em> = 1, due to geometric constraints upon <em>A</em>′ for La substitution between the two different subunits. The magnetic properties strongly depend on the structure type and the <em>A</em>′ content. Hexagonal La<sub>2</sub>Ni<sub>7</sub> is a weak antiferromagnet (wAFM) at low field and temperature and undergoes metamagnetic transitions towards weak ferromagnetic state (wFM) under applied field. Under an applied field of 0.1 T, La<sub>2−</sub><em><sub>x</sub>A</em>′<em><sub>x</sub></em>Ni<sub>7</sub> intermetallic compounds display two different transition temperatures <em>T</em><sub>1</sub> and <em>T</em><sub>2</sub> that both increase with <em>x</em>. <em>T</em><sub>1</sub> is associated with a wFM-wAFM transition in the 2<em>H</em> phase for <em>A</em>′ = Sm, whereas <em>T</em><sub>2</sub> is related to the Curie temperature of both 2<em>H</em> and 3<em>R</em> phases. A metamagnetic behaviour is observed between <em>T</em><sub>1</sub> and <em>T</em><sub>2</sub> with transition field <em>µ<sub>0</sub>H</em><sub>Trans</sub> between 2 and 3.5 T for compounds with <em>A</em>′ = Sm. The La<sub>2−</sub><em><sub>x</sub></em>Sm<em><sub>x</sub></em>Ni<sub>7</sub> compounds (<em>x</em> > 0) behave as hard magnets with a large coercive field <em>µ</em><sub>0</sub><em>H</em><sub>C</sub> at low temperature (<em>µ</em><sub>0</sub><em>H</em><sub>C</sub> > 9 T at 5 K for <em>x</em> = 2), whereas the La<sub>2−</sub><em><sub>x</sub></em>Gd<em><sub>x</sub></em>Ni<sub>7</sub> compounds (<em>x</em> > 0) are soft ferrimagnets with a linear increase of the saturation magnetization versus Gd content.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"618 ","pages":"Article 172859"},"PeriodicalIF":2.5,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143418974","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-07DOI: 10.1016/j.jmmm.2025.172839
Karl Fabian, Annemarieke Béguin
Micromagnetism historically started with the analysis of the approach-to-saturation (ATS) of hysteresis loops of ferromagnetic materials. For soft magnetic particulate samples the ATS behavior at varying temperatures depends strongly on magnetostatically controlled shape anisotropy. Scaling micromagnetic energies by demagnetizing energy, the scaled reversible work (SRW) due to demagnetizing energy becomes independent of temperature. Observed temperature variations in SRW can therefore be attributed to other micromagnetic energy terms which may be identified through the known temperature variations of magnetostriction and magnetocrystalline anisotropy constants. A detailed analysis of the temperature variation of SRW can therefore separate the energy contributions of magnetostatic interaction, internal stress, and magnetocrystalline anisotropy. For homogeneous magnetizations it is possible to calculate calibration curves to estimate stress in soft magnetic materials. Three-dimensional micromagnetic calculations provide a more detailed view of grain-size dependent mechanisms of SRW in soft magnetic materials like Ni, Co, Fe, and FeO.
{"title":"Temperature dependent approach-to-saturation in soft-magnetic particle assemblages: Separating work against stress and demagnetization","authors":"Karl Fabian, Annemarieke Béguin","doi":"10.1016/j.jmmm.2025.172839","DOIUrl":"10.1016/j.jmmm.2025.172839","url":null,"abstract":"<div><div>Micromagnetism historically started with the analysis of the approach-to-saturation (ATS) of hysteresis loops of ferromagnetic materials. For soft magnetic particulate samples the ATS behavior at varying temperatures depends strongly on magnetostatically controlled shape anisotropy. Scaling micromagnetic energies by demagnetizing energy, the scaled reversible work (SRW) due to demagnetizing energy becomes independent of temperature. Observed temperature variations in SRW can therefore be attributed to other micromagnetic energy terms which may be identified through the known temperature variations of magnetostriction and magnetocrystalline anisotropy constants. A detailed analysis of the temperature variation of SRW can therefore separate the energy contributions of magnetostatic interaction, internal stress, and magnetocrystalline anisotropy. For homogeneous magnetizations it is possible to calculate calibration curves to estimate stress in soft magnetic materials. Three-dimensional micromagnetic calculations provide a more detailed view of grain-size dependent mechanisms of SRW in soft magnetic materials like Ni, Co, Fe, and Fe<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span>.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"617 ","pages":"Article 172839"},"PeriodicalIF":2.5,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143386643","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In order to improve the damping performance of the vehicle chassis suspension system, a new electromagnetic radial magnetorheological damper (ER-MRD) with discontinuous sector ring damping channel is proposed in this paper. The structural design of ER-MRD was carried out, and magnetic field simulation was performed on it. The prototype of the ER-MRD was manufactured, and the damping performance test was carried out on the electro-hydraulic servo test bench. Effect of current, amplitude and frequency on the damping performance of ER-MRD was investigated respectively. The experimental results show that the maximum damping force of ER-MRD is 765 N when the input current is 0A. When the input current is 2A, the frequency is 2 Hz and the amplitude is 10 mm, the damping force peak output of ER-MRD reaches 3850 N. The maximum adjustable damping ratio of ER-MRD during the experiment is 6.29.
{"title":"Design and experimental study of a new type of electromagnetic radial magnetorheological damper","authors":"Xiaolong Yang, Denghui Li, Kangjun Li, Qingqing Xin","doi":"10.1016/j.jmmm.2025.172852","DOIUrl":"10.1016/j.jmmm.2025.172852","url":null,"abstract":"<div><div>In order to improve the damping performance of the vehicle chassis suspension system, a new electromagnetic radial magnetorheological damper (ER-MRD) with discontinuous sector ring damping channel is proposed in this paper. The structural design of ER-MRD was carried out, and magnetic field simulation was performed on it. The prototype of the ER-MRD was manufactured, and the damping performance test was carried out on the electro-hydraulic servo test bench. Effect of current, amplitude and frequency on the damping performance of ER-MRD was investigated respectively. The experimental results show that the maximum damping force of ER-MRD is 765 N when the input current is 0A. When the input current is 2A, the frequency is 2 Hz and the amplitude is 10 mm, the damping force peak output of ER-MRD reaches 3850 N. The maximum adjustable damping ratio of ER-MRD during the experiment is 6.29.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"618 ","pages":"Article 172852"},"PeriodicalIF":2.5,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143419334","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-06DOI: 10.1016/j.jmmm.2025.172843
N. Maniotis , M. Gitsou , M. Maragakis
Magnetic nanoparticles (MNPs) have garnered substantial interest in recent years due to their promising applications in biomedicine, particularly in magnetic hyperthermia, drug delivery, and magnetic resonance imaging. Among these applications, magnetic hyperthermia stands out as a potential cancer treatment method, wherein MNPs are introduced into the body and subjected to an alternating magnetic field to induce localized heating. The efficacy of this treatment is often quantified by the Specific Loss Power (SLP) index, which measures the rate of heat dissipation from the nanoparticles. Understanding and optimizing the factors that influence SLP is crucial for enhancing the effectiveness of magnetic hyperthermia. One of the critical parameters affecting the performance of MNPs in hyperthermia is their magnetic anisotropy, which refers to the directional dependence of their magnetic properties. Magnetic anisotropy can significantly influence the relaxation mechanisms of MNPs and, consequently, their heating efficiency. Another important factor is the dipolar interactions between nanoparticles. These interactions, which arise from the magnetic fields generated by neighboring particles, can lead to complex collective behaviors that impact the overall heating performance. In this study, we investigated the thermal efficiencies of MNPs for hyperthermia applications, focusing on the effects of anisotropy and dipolar interactions. Utilizing micromagnetic simulations, we quantitatively analyzed the SLP of MNPs with varying uniaxial shape anisotropy and concentrations. The simulations were conducted under a magnetic field of 30 mT amplitude and 765 kHz frequency, with typical magnetite nanoparticles of 30 nm in size. We present a thorough analysis for a deeper understanding of how magnetic anisotropy and dipolar interactions interplay to affect the hyperthermic properties of MNPs by conjugating anisotropy to dipolar interactions and examine the resultant effect on the SLP index through comprehensive micromagnetic simulations. By systematically varying the anisotropy constants and analyzing the dipolar coupling among nanoparticles, we established a clear relationship between these parameters and the hyperthermic efficiency.
{"title":"Conjugating magnetic nanoparticles anisotropy to their dipolar interactions: Effect on the hyperthermic losses index via micromagnetic simulations","authors":"N. Maniotis , M. Gitsou , M. Maragakis","doi":"10.1016/j.jmmm.2025.172843","DOIUrl":"10.1016/j.jmmm.2025.172843","url":null,"abstract":"<div><div>Magnetic nanoparticles (MNPs) have garnered substantial interest in recent years due to their promising applications in biomedicine, particularly in magnetic hyperthermia, drug delivery, and magnetic resonance imaging. Among these applications, magnetic hyperthermia stands out as a potential cancer treatment method, wherein MNPs are introduced into the body and subjected to an alternating magnetic field to induce localized heating. The efficacy of this treatment is often quantified by the Specific Loss Power (SLP) index, which measures the rate of heat dissipation from the nanoparticles. Understanding and optimizing the factors that influence SLP is crucial for enhancing the effectiveness of magnetic hyperthermia. One of the critical parameters affecting the performance of MNPs in hyperthermia is their magnetic anisotropy, which refers to the directional dependence of their magnetic properties. Magnetic anisotropy can significantly influence the relaxation mechanisms of MNPs and, consequently, their heating efficiency. Another important factor is the dipolar interactions between nanoparticles. These interactions, which arise from the magnetic fields generated by neighboring particles, can lead to complex collective behaviors that impact the overall heating performance. In this study, we investigated the thermal efficiencies of MNPs for hyperthermia applications, focusing on the effects of anisotropy and dipolar interactions. Utilizing micromagnetic simulations, we quantitatively analyzed the SLP of MNPs with varying uniaxial shape anisotropy and concentrations. The simulations were conducted under a magnetic field of 30 mT amplitude and 765 kHz frequency, with typical magnetite nanoparticles of 30 nm in size. We present a thorough analysis for a deeper understanding of how magnetic anisotropy and dipolar interactions interplay to affect the hyperthermic properties of MNPs by conjugating anisotropy to dipolar interactions and examine the resultant effect on the SLP index through comprehensive micromagnetic simulations. By systematically varying the anisotropy constants and analyzing the dipolar coupling among nanoparticles, we established a clear relationship between these parameters and the hyperthermic efficiency.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"617 ","pages":"Article 172843"},"PeriodicalIF":2.5,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143372557","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-06DOI: 10.1016/j.jmmm.2025.172853
Linjie Xu , Guangyuan Weng , Kejie Zhao , Zhaoyang Han , Yao Zhai , Xinlei Xing , Jie Zheng , Xiyu Zhu , Le Wang , Tianping Gu , Bo Wang
To investigate the mechanism of coupling between the hydrogen charging time and magnetic-stress properties of hydrogen-charged pipeline steel, theoretical analyses and experimental studies were conducted to characterize its magnetic, mechanical and magnetic-stress coupling properties using pipeline steel specimens of different grades under an electrochemical hydrogen charging environment. The hydrogen charging environment simulation test platform was constructed, and 100 test specimens of X52, X60, X70, and X80 pipeline steel with various hydrogen charging times were prepared. The magnetic flux change curves in the length direction of specimens were tested using the TD8900 magnetic flux test instrument. Tensile tests were employed to obtain the stress–strain curves of specimens with different hydrogen charging times, and the micromorphology of specimen fracture was examined using a scanning electron microscope (SEM). By testing the curves of specimens with different hydrogen charging times, changes in the saturation field and saturation magnetization strength induced by hydrogen intrusion into pipeline steel were analyzed. In addition, the coupling model of hydrogen charging time, magnetic property parameter, and mechanical property parameter of specimens under different working conditions was determined. It was found that the magnetic property parameters of pipeline steel specimens exhibited significant changes as the hydrogen charging time increased. The magnetic flux of the same cross-section in the specimen’s length direction decreased. Similarly, the stress–strain of specimens with different hydrogen charging times showed significant alterations. The ultimate strain value of the fracture decreased significantly with the hydrogen charging time. The results provide new ideas and methods for quantitatively evaluating hydrogen embrittlement based on magnetic-stress characteristics.
{"title":"Magnetic-stress coupling test of pipeline steel after magnetization saturation with different hydrogen charging times","authors":"Linjie Xu , Guangyuan Weng , Kejie Zhao , Zhaoyang Han , Yao Zhai , Xinlei Xing , Jie Zheng , Xiyu Zhu , Le Wang , Tianping Gu , Bo Wang","doi":"10.1016/j.jmmm.2025.172853","DOIUrl":"10.1016/j.jmmm.2025.172853","url":null,"abstract":"<div><div>To investigate the mechanism of coupling between the hydrogen charging time and magnetic-stress properties of hydrogen-charged pipeline steel, theoretical analyses and experimental studies were conducted to characterize its magnetic, mechanical and magnetic-stress coupling properties using pipeline steel specimens of different grades under an electrochemical hydrogen charging environment. The hydrogen charging environment simulation test platform was constructed, and 100 test specimens of X52, X60, X70, and X80 pipeline steel with various hydrogen charging times were prepared. The magnetic flux change curves in the length direction of specimens were tested using the TD8900 magnetic flux test instrument. Tensile tests were employed to obtain the stress–strain curves of specimens with different hydrogen charging times, and the micromorphology of specimen fracture was examined using a scanning electron microscope (SEM). By testing the <span><math><mrow><mi>M</mi><mo>-</mo><mi>H</mi></mrow></math></span> curves of specimens with different hydrogen charging times, changes in the saturation field <span><math><msub><mi>H</mi><mtext>S</mtext></msub></math></span> and saturation magnetization strength <span><math><msub><mi>M</mi><mtext>S</mtext></msub></math></span> induced by hydrogen intrusion into pipeline steel were analyzed. In addition, the coupling model of hydrogen charging time, magnetic property parameter, and mechanical property parameter of specimens under different working conditions was determined. It was found that the magnetic property parameters of pipeline steel specimens exhibited significant changes as the hydrogen charging time increased. The magnetic flux of the same cross-section in the specimen’s length direction decreased. Similarly, the stress–strain of specimens with different hydrogen charging times showed significant alterations. The ultimate strain value of the fracture decreased significantly with the hydrogen charging time. The results provide new ideas and methods for quantitatively evaluating hydrogen embrittlement based on magnetic-stress characteristics.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"617 ","pages":"Article 172853"},"PeriodicalIF":2.5,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143376988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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