In this work, we investigate the effect of alloying on the magnetic properties of the semiconductor ferromagnetic GeFe/Ge(001) superlattice. The system Hamiltonian is described within the localized-spin Heisenberg model. The excitation spectrum is calculated using linear spin-wave theory. A quantitative analysis of the experimental magnetization data reveals the existence of a spin reorientation transition (SRT) at the inflection temperature (). To explain the behavior of this magnetization, we have developed a theoretical model based on the presence of a mixture of two magnon populations: quantum magnons and classical magnons. Furthermore, the agreement between the calculated and experimental magnetization curves is very satisfactory, enabling the determination of the key magnetic parameters of the system, namely, , , , and .
{"title":"Alloying effect on the magnetic and magnonic properties of a thin-film superlattice based on the magnetic semiconductor Ge1−xFex/Ge","authors":"Marouan Karam, Atika Fahmi, Ahmed Qachaou, Mounir Fahoume, Ismail Benaicha, Jaouad Mhalla, Abderrahim Raidou, Mohamed Lharch","doi":"10.1016/j.jmmm.2025.173787","DOIUrl":"10.1016/j.jmmm.2025.173787","url":null,"abstract":"<div><div>In this work, we investigate the effect of alloying on the magnetic properties of the semiconductor ferromagnetic Ge<span><math><msub><mrow></mrow><mrow><mn>1</mn><mo>−</mo><mi>x</mi></mrow></msub></math></span>Fe<span><math><msub><mrow></mrow><mrow><mi>x</mi></mrow></msub></math></span>/Ge(001) superlattice. The system Hamiltonian is described within the localized-spin Heisenberg model. The excitation spectrum is calculated using linear spin-wave theory. A quantitative analysis of the experimental magnetization data reveals the existence of a spin reorientation transition (SRT) at the inflection temperature (<span><math><mrow><mi>T</mi><mo>=</mo><msub><mrow><mi>T</mi></mrow><mrow><mi>r</mi></mrow></msub></mrow></math></span>). To explain the behavior of this magnetization, we have developed a theoretical model based on the presence of a mixture of two magnon populations: quantum magnons and classical magnons. Furthermore, the agreement between the calculated and experimental magnetization curves is very satisfactory, enabling the determination of the key magnetic parameters of the system, namely, <span><math><mrow><msub><mrow><mi>J</mi></mrow><mrow><mo>∥</mo></mrow></msub><mrow><mo>(</mo><mi>x</mi><mo>)</mo></mrow></mrow></math></span>, <span><math><mrow><msub><mrow><mi>J</mi></mrow><mrow><mo>⊥</mo></mrow></msub><mrow><mo>(</mo><mi>x</mi><mo>)</mo></mrow></mrow></math></span>, <span><math><mrow><mi>Δ</mi><mrow><mo>(</mo><mi>x</mi><mo>)</mo></mrow></mrow></math></span>, and <span><math><mrow><msub><mrow><mi>T</mi></mrow><mrow><mi>r</mi></mrow></msub><mrow><mo>(</mo><mi>x</mi><mo>)</mo></mrow></mrow></math></span>.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"640 ","pages":"Article 173787"},"PeriodicalIF":3.0,"publicationDate":"2025-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145882789","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 : 2025-12-29DOI: 10.1016/j.jmmm.2025.173790
Zikai Wu , Hongsheng Chen , Zhongge Luo , Chen Wang , Jiayi He , Kuangxin Luo , Haojun Zhou , Fenghua Luo
Cerium (Ce) is a high-quality substitute for Pr/Nd in Nd–Fe–B magnets due to its low cost and abundant natural reserves. However, the coercivity (Hcj) of Re–Fe–B magnets with high Ce content is difficult to improve due to the aggregation of ReFe2 phase at the triple junctions. This study investigated the grain boundary reconstruction in Nd-Ce-Fe-B sintered magnets using Pr–Nd–Cu–Ga prealloyed powder. The results indicate that as the addition amount of Pr–Nd–Cu–Ga increases, Hcj gradually increases. When the addition amount is 4 wt%, the maximum Hcj of the obtained magnet at a remanence of 11.5 kGs is 14.8 kOe. Grain boundary reconstruction promotes the continuous formation of ReFe2 and other rare earth rich phases at grain boundaries, promoting the forming of thicker grain boundary layers and improving magnetic isolation. Furthermore, Pr–Nd–Cu–Ga leads to an increase in ReFe2 phase; Cu and Ga can enhance the stability of ReFe2 phase, while Nd partially replaces Ce in the grain boundary ReFe2 phase, forming a new Nd–dominated 1:2 phase that enhances magnet wettability. The results advance the understanding of the ReFe2 phase and provide critical insights for developing low–cost Nd–Ce–Fe–B magnets with high Hcj.
{"title":"Optimizing Nd–Ce–Fe–B grain boundary structure by Pr–Nd–Cu–Ga prealloyed powder to enhance coercivity","authors":"Zikai Wu , Hongsheng Chen , Zhongge Luo , Chen Wang , Jiayi He , Kuangxin Luo , Haojun Zhou , Fenghua Luo","doi":"10.1016/j.jmmm.2025.173790","DOIUrl":"10.1016/j.jmmm.2025.173790","url":null,"abstract":"<div><div>Cerium (Ce) is a high-quality substitute for Pr/Nd in Nd–Fe–B magnets due to its low cost and abundant natural reserves. However, the coercivity (H<sub>cj</sub>) of Re–Fe–B magnets with high Ce content is difficult to improve due to the aggregation of ReFe<sub>2</sub> phase at the triple junctions. This study investigated the grain boundary reconstruction in Nd-Ce-Fe-B sintered magnets using Pr–Nd–Cu–Ga prealloyed powder. The results indicate that as the addition amount of Pr–Nd–Cu–Ga increases, H<sub>cj</sub> gradually increases. When the addition amount is 4 wt%, the maximum H<sub>cj</sub> of the obtained magnet at a remanence of 11.5 kGs is 14.8 kOe. Grain boundary reconstruction promotes the continuous formation of ReFe<sub>2</sub> and other rare earth rich phases at grain boundaries, promoting the forming of thicker grain boundary layers and improving magnetic isolation. Furthermore, Pr–Nd–Cu–Ga leads to an increase in ReFe<sub>2</sub> phase; Cu and Ga can enhance the stability of ReFe<sub>2</sub> phase, while Nd partially replaces Ce in the grain boundary ReFe<sub>2</sub> phase, forming a new Nd–dominated 1:2 phase that enhances magnet wettability. The results advance the understanding of the ReFe<sub>2</sub> phase and provide critical insights for developing low–cost Nd–Ce–Fe–B magnets with high H<sub>cj</sub>.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"640 ","pages":"Article 173790"},"PeriodicalIF":3.0,"publicationDate":"2025-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145882787","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}
Polycrystalline Cu2OSeO3 was synthesized via a solid-state reaction method, and its phase purity was confirmed through X-ray diffraction followed by Rietveld refinement. The compound features two distinct crystallographic copper sites: Cu(I) in a trigonal bipyramidal configuration and Cu(II) in a square pyramidal arrangement, present in a 1:3 ratio. This unique structure leads to complex magnetic interactions between the sites. Magnetic properties were investigated using DC magnetization and AC susceptibility measurements. The material exhibits a delicate balance of symmetric superexchange interactions, antisymmetric Dzyaloshinskii-Moriya (DM) interaction, magnetocrystalline anisotropy, and Zeeman energy, resulting in various intricate magnetic phases. These include fluctuation disorder (FD), helical, skyrmion mixed conical and tilted spiral, conical, field-polarized ferrimagnetism, and importantly, the skyrmion phase. Additionally, the magnetocaloric effect was studied through temperature-dependent heat capacity measurements under different magnetic fields. The findings indicate reasonable magnetic refrigeration capabilities, with maximum magnetic entropy changes of 2.23 J/kg·K and 4.25 J/kg·K at around 60 K for field changes of 4 T and 7 T, respectively. The corresponding maximum relative cooling powers are determined to be 67 J/Kg and 140 J/kg. The critical correlation was also investigated through the magnetocaloric effect, demonstrating 3D Heisenberg interaction above the paramagnetic to FD transition temperature (Tc), accompanied by short-range magnetic correlations. Furthermore, the universal behavior of the normalized magnetic entropy-change curve confirms the presence of a second-order magnetic phase transition near Tc under high magnetic fields.
{"title":"Investigation of magnetic phase transition and critical behavior in Cu2OSeO3 via magnetocaloric effect","authors":"Sudipta Mahana , Prasanta Kumar Behera , Keshab Chandra Prusty , Pronoy Nandi , Dinesh Topwal","doi":"10.1016/j.jmmm.2025.173791","DOIUrl":"10.1016/j.jmmm.2025.173791","url":null,"abstract":"<div><div>Polycrystalline Cu<sub>2</sub>OSeO<sub>3</sub> was synthesized via a solid-state reaction method, and its phase purity was confirmed through X-ray diffraction followed by Rietveld refinement. The compound features two distinct crystallographic copper sites: Cu(I) in a trigonal bipyramidal configuration and Cu(II) in a square pyramidal arrangement, present in a 1:3 ratio. This unique structure leads to complex magnetic interactions between the sites. Magnetic properties were investigated using DC magnetization and AC susceptibility measurements. The material exhibits a delicate balance of symmetric superexchange interactions, antisymmetric Dzyaloshinskii-Moriya (DM) interaction, magnetocrystalline anisotropy, and Zeeman energy, resulting in various intricate magnetic phases. These include fluctuation disorder (FD), helical, skyrmion mixed conical and tilted spiral, conical, field-polarized ferrimagnetism, and importantly, the skyrmion phase. Additionally, the magnetocaloric effect was studied through temperature-dependent heat capacity measurements under different magnetic fields. The findings indicate reasonable magnetic refrigeration capabilities, with maximum magnetic entropy changes of 2.23 J/kg·K and 4.25 J/kg·K at around 60 K for field changes of 4 T and 7 T, respectively. The corresponding maximum relative cooling powers are determined to be 67 J/Kg and 140 J/kg. The critical correlation was also investigated through the magnetocaloric effect, demonstrating 3D Heisenberg interaction above the paramagnetic to FD transition temperature (<em>T</em><sub><em>c</em></sub>), accompanied by short-range magnetic correlations. Furthermore, the universal behavior of the normalized magnetic entropy-change curve confirms the presence of a second-order magnetic phase transition near <em>T</em><sub><em>c</em></sub> under high magnetic fields.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"640 ","pages":"Article 173791"},"PeriodicalIF":3.0,"publicationDate":"2025-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145882788","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 : 2025-12-29DOI: 10.1016/j.jmmm.2025.173794
Dongliang Guo , Xinteng Shen , Xiangtao Yu , Min Lin , Yingli Sun , Yong Ding , Aru Yan
The effects of quenching temperature (800–1000 °C) on the key properties of Fe61Ni32Co7 low-expansion alloy are investigated, which reveals that quenching temperature significantly regulates the alloy's grain size and performance. The core findings indicate that the alloy achieves a synergistic optimization of high-temperature soft magnetic properties and low expansion characteristics under a quenching temperature of 950 °C. At this temperature, the alloy exhibits excellent overall soft magnetic performance at 200 °C: saturated magnetic flux density rises markedly to 973.7mT, maximum permeability increases dramatically (about 5.6 times higher than the original state), and coercivity is significantly reduced by 85%. Notably, the coefficient of thermal expansion in this optimized state remains at a low level (2.199 × 10−⁶/°C). The performance enhancement mechanism mainly stems from the full release of residual stress induced by quenching (recrystallized region >94%), optimization of magnetic domain structure (reduction of domain wall energy) and the effect of high Curie temperature in extending the temperature range for magnetostriction. This research provides crucial process guidance for the development of FeNiCo alloys with excellent high-temperature soft magnetic properties and stable low-expansion characteristics, which contributes to precision instruments and high-sensitivity sensors that require stringent thermal and magnetic stability.
{"title":"The influence of quenching temperature on the high-temperature properties and microstructure of FeNiCo alloys","authors":"Dongliang Guo , Xinteng Shen , Xiangtao Yu , Min Lin , Yingli Sun , Yong Ding , Aru Yan","doi":"10.1016/j.jmmm.2025.173794","DOIUrl":"10.1016/j.jmmm.2025.173794","url":null,"abstract":"<div><div>The effects of quenching temperature (800–1000 °C) on the key properties of Fe<sub>61</sub>Ni<sub>32</sub>Co<sub>7</sub> low-expansion alloy are investigated, which reveals that quenching temperature significantly regulates the alloy's grain size and performance. The core findings indicate that the alloy achieves a synergistic optimization of high-temperature soft magnetic properties and low expansion characteristics under a quenching temperature of 950 °C. At this temperature, the alloy exhibits excellent overall soft magnetic performance at 200 °C: saturated magnetic flux density rises markedly to 973.7mT, maximum permeability increases dramatically (about 5.6 times higher than the original state), and coercivity is significantly reduced by 85%. Notably, the coefficient of thermal expansion in this optimized state remains at a low level (2.199 × 10<sup>−</sup>⁶/°C). The performance enhancement mechanism mainly stems from the full release of residual stress induced by quenching (recrystallized region >94%), optimization of magnetic domain structure (reduction of domain wall energy) and the effect of high Curie temperature in extending the temperature range for magnetostriction. This research provides crucial process guidance for the development of FeNiCo alloys with excellent high-temperature soft magnetic properties and stable low-expansion characteristics, which contributes to precision instruments and high-sensitivity sensors that require stringent thermal and magnetic stability.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"640 ","pages":"Article 173794"},"PeriodicalIF":3.0,"publicationDate":"2025-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145882793","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 : 2025-12-29DOI: 10.1016/j.jmmm.2025.173793
Yulin Pan, Yong Li
In this paper, the structural characteristics, magnetic properties and magnetocaloric performance of a series of high-entropy alloys (HEAs) Mn20Co20Ni20Fe26+xCu14-x (x = 0, 2, 4) have been experimentally determined and theoretically analyzed. The results showed that these alloys have a disordered FCC crystal structure. The Fe concentration determines the temperature range within which the ferromagnetic behavior and Curie temperatures can be adjusted. In particular, it decreases from 274 K for Fe26Cu14 to 242 K for Fe30Cu10. In addition, the maximum magnetic entropy change values are obtained in the magnetic field change of 7 T for 1.37, 1.28 and 1.33 J/kgK were obtained for x = 0, 2 and 4, respectively. Compared to other transition metal-based high-entropy alloys reported in the literatures, the present material shows comparable or superior performance. The experimental characterization results are in good agreement with the theoretical predictions and affords an extensive series of rare-earth-free HEAs exhibiting pronounced magnetocaloric properties.
{"title":"Magnetic phase transition and magnetocaloric effect in rare-earth-free high entropy alloys MnCoNiFeCu","authors":"Yulin Pan, Yong Li","doi":"10.1016/j.jmmm.2025.173793","DOIUrl":"10.1016/j.jmmm.2025.173793","url":null,"abstract":"<div><div>In this paper, the structural characteristics, magnetic properties and magnetocaloric performance of a series of high-entropy alloys (HEAs) Mn<sub>20</sub>Co<sub>20</sub>Ni<sub>20</sub>Fe<sub>26+x</sub>Cu<sub>14-x</sub> (x = 0, 2, 4) have been experimentally determined and theoretically analyzed. The results showed that these alloys have a disordered FCC crystal structure. The Fe concentration determines the temperature range within which the ferromagnetic behavior and Curie temperatures can be adjusted. In particular, it decreases from 274 K for Fe<sub>26</sub>Cu<sub>14</sub> to 242 K for Fe<sub>30</sub>Cu<sub>10</sub>. In addition, the maximum magnetic entropy change values are obtained in the magnetic field change of 7 T for 1.37, 1.28 and 1.33 J/kgK were obtained for x <em>=</em> 0, 2 and 4, respectively. Compared to other transition metal-based high-entropy alloys reported in the literatures, the present material shows comparable or superior performance. The experimental characterization results are in good agreement with the theoretical predictions and affords an extensive series of rare-earth-free HEAs exhibiting pronounced magnetocaloric properties.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"641 ","pages":"Article 173793"},"PeriodicalIF":3.0,"publicationDate":"2025-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145941220","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 : 2025-12-28DOI: 10.1016/j.jmmm.2025.173785
Yasin Yılmaz , Muhammed Fatih Kılıçaslan
NdFeB permanent magnetic alloys are widely used in industrial applications, particularly in electronics, due to their excellent magnetic performance. However, their dependence on expensive rare earth and neodymium elements has led to supply risks and price instability. As a more abundant and economical alternative, CeFeB alloys have gained attention recently. In this study, CeFeB ribbons with a nominal composition of Ce₃₅Fe₆₄B₁ (wt%) were fabricated via melt spinning method at different wheel surface speeds (3–35 m/s). XRD analysis revealed that all of the ribbon samples exhibit partially crystalline structures. They contains the Ce₂Fe₁₄B hard magnetic phase, along with soft magnetic α-Fe and paramagnetic CeFe₂ phases. As the wheel surface speed increased, crystallite size of the Ce₂Fe₁₄B phase reduced, and tendency to amorphous phase formation increased. The finest crystallite size of the Ce₂Fe₁₄B phase of 26.18 nm was achieved at the wheel surface speed of 5 m/s. Accordingly, the optimum magnetic properties were obtained. These are the coercivity, remanence, maximum energy product, and remanence ratio of 4301.84 Oe, 62.12 emu/g, 10.94 MGOe, and 0.624, respectively. These results highlight the critical role of cooling rate for modifying the microstructure and improving the magnetic performance. This study shows that the CeFeB alloys posses the requisite magnetic performance to serve as competitive, low-cost alternatives to their NdFeB counterparts. Their favorable characteristics highlight a strong potential for integration into large-scale industrial systems where rare earth scarcity and economic viability are of primary concern.
{"title":"Effect of cooling rate on the microstructure and magnetic properties of melt-spun CeFeB ribbons","authors":"Yasin Yılmaz , Muhammed Fatih Kılıçaslan","doi":"10.1016/j.jmmm.2025.173785","DOIUrl":"10.1016/j.jmmm.2025.173785","url":null,"abstract":"<div><div>NdFeB permanent magnetic alloys are widely used in industrial applications, particularly in electronics, due to their excellent magnetic performance. However, their dependence on expensive rare earth and neodymium elements has led to supply risks and price instability. As a more abundant and economical alternative, CeFeB alloys have gained attention recently. In this study, CeFeB ribbons with a nominal composition of Ce₃₅Fe₆₄B₁ (wt%) were fabricated via melt spinning method at different wheel surface speeds (3–35 m/s). XRD analysis revealed that all of the ribbon samples exhibit partially crystalline structures. They contains the Ce₂Fe₁₄B hard magnetic phase, along with soft magnetic α-Fe and paramagnetic CeFe₂ phases. As the wheel surface speed increased, crystallite size of the Ce₂Fe₁₄B phase reduced, and tendency to amorphous phase formation increased. The finest crystallite size of the Ce₂Fe₁₄B phase of 26.18 nm was achieved at the wheel surface speed of 5 m/s. Accordingly, the optimum magnetic properties were obtained. These are the coercivity, remanence, maximum energy product, and remanence ratio of 4301.84 Oe, 62.12 emu/g, 10.94 MGOe, and 0.624, respectively. These results highlight the critical role of cooling rate for modifying the microstructure and improving the magnetic performance. This study shows that the CeFeB alloys posses the requisite magnetic performance to serve as competitive, low-cost alternatives to their NdFeB counterparts. Their favorable characteristics highlight a strong potential for integration into large-scale industrial systems where rare earth scarcity and economic viability are of primary concern.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"640 ","pages":"Article 173785"},"PeriodicalIF":3.0,"publicationDate":"2025-12-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145882790","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 : 2025-12-27DOI: 10.1016/j.jmmm.2025.173789
Yanjun Qin , Xiaozhen Fan , Zheng Fang , Jianqiang Zhang , Jingui Li , Huiqun Ye , Jinju Zheng , Yunzhang Fang
Amorphous and nanocrystalline alloys possess substantial potential for sensor applications due to their superior soft magnetic characteristics and large giant stress-impedance (GSI) effect. This investigation elucidates the mechanisms by which stress annealing modulates the longitudinally-driven GSI (LDGSI) effect in Fe73.5Cu1Nb3Si13.5B9 amorphous ribbons. Samples subjected to tensile stresses of varying magnitudes during annealing were analyzed using synchrotron X-ray diffraction (XRD), high-resolution transmission electron microscopy (TEM), and magnetic measurements to establish correlations between stress-induced magnetic anisotropy and GSI behavior. The sample annealed at 18 MPa demonstrated optimal performance, achieving an LDGSI ratio of 1031 %, significantly exceeding that of the conventional transverse-driven configuration. Microstructural characterization revealed that stress annealing promotes lattice anisotropy in α-Fe(Si) nanocrystals and modulates the magnetic anisotropy constant (Ku) via residual elastic strain, thereby affecting effective permeability (μe) and impedance response. Magnetic domain imaging confirmed that enhanced transverse magnetic anisotropy is a decisive factor in achieving superior GSI performance. These results contribute to the informed design and optimization of advanced GSI sensor materials.
{"title":"Stress-induced magnetic anisotropy and its role in the longitudinal giant stress-impedance effect of Fe-based alloys","authors":"Yanjun Qin , Xiaozhen Fan , Zheng Fang , Jianqiang Zhang , Jingui Li , Huiqun Ye , Jinju Zheng , Yunzhang Fang","doi":"10.1016/j.jmmm.2025.173789","DOIUrl":"10.1016/j.jmmm.2025.173789","url":null,"abstract":"<div><div>Amorphous and nanocrystalline alloys possess substantial potential for sensor applications due to their superior soft magnetic characteristics and large giant stress-impedance (GSI) effect. This investigation elucidates the mechanisms by which stress annealing modulates the longitudinally-driven GSI (LDGSI) effect in Fe<sub>73.5</sub>Cu<sub>1</sub>Nb<sub>3</sub>Si<sub>13.5</sub>B<sub>9</sub> amorphous ribbons. Samples subjected to tensile stresses of varying magnitudes during annealing were analyzed using synchrotron X-ray diffraction (XRD), high-resolution transmission electron microscopy (TEM), and magnetic measurements to establish correlations between stress-induced magnetic anisotropy and GSI behavior. The sample annealed at 18 MPa demonstrated optimal performance, achieving an LDGSI ratio of 1031 %, significantly exceeding that of the conventional transverse-driven configuration. Microstructural characterization revealed that stress annealing promotes lattice anisotropy in <em>α</em>-Fe(Si) nanocrystals and modulates the magnetic anisotropy constant (<em>K</em><sub><em>u</em></sub>) via residual elastic strain, thereby affecting effective permeability (μ<sub><em>e</em></sub>) and impedance response. Magnetic domain imaging confirmed that enhanced transverse magnetic anisotropy is a decisive factor in achieving superior GSI performance. These results contribute to the informed design and optimization of advanced GSI sensor materials.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"639 ","pages":"Article 173789"},"PeriodicalIF":3.0,"publicationDate":"2025-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145881452","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 : 2025-12-27DOI: 10.1016/j.jmmm.2025.173786
Ahmadreza Nematolahi, Ghasem Dini, Fereshteh Mahmoodiyan Najafabadi, Maryam Abdollahi Asl
Dual-mode (T₁–T₂) magnetic resonance imaging (MRI) contrast agents offer improved diagnostic capability through simultaneous longitudinal and transverse relaxation enhancement. In this work, quasi-spherical and cubic NiFe₂O₄ nanoparticles were synthesized via a hydrothermal process by varying reaction time and subsequently coated with polyethylene glycol (PEG) to enhance colloidal stability. The quasi-spherical nanoparticles synthesized for 12 h exhibited an average diameter of ∼25 nm and a saturation magnetization (Mₛ) of 49 emu·g−1, whereas the cubic nanoparticles obtained after 24 h displayed an edge length of ∼65 nm with Mₛ = ∼ 67 emu·g−1. T₁- and T₂-weighted MRI measurements revealed that particle size and surface modification strongly influenced relaxivity. The 25 nm sample showed optimal dual-mode performance, with r₁ = 5.7 mM−1·s−1 and r₂ = 103.1 mM−1·s−1 (r₂/r₁ = ∼18), while PEG coating slightly reduced both relaxivities due to magnetic shielding but significantly improved dispersion stability. 65 nm cubic nanoparticles exhibited high r₂ (153.4 mM−1·s−1), confirming their suitability for T₂-weighted imaging. In vitro MTT cytotoxicity assays on HepG2 cells at 200 μg·mL−1 demonstrated low toxicity, with cell viability exceeding 80 % after 72 h across all samples and > 94 % for PEG-coated variants. These results demonstrate that controlled morphology and surface engineering of NiFe₂O₄ nanoparticles can effectively tune their magnetic and relaxometric properties, enabling their application as efficient T₁–T₂ dual-mode MRI contrast agents.
{"title":"Synthesis and characterization of nickel ferrite (NiFe₂O₄) nanoparticles as dual T₁–T₂ MRI contrast agents","authors":"Ahmadreza Nematolahi, Ghasem Dini, Fereshteh Mahmoodiyan Najafabadi, Maryam Abdollahi Asl","doi":"10.1016/j.jmmm.2025.173786","DOIUrl":"10.1016/j.jmmm.2025.173786","url":null,"abstract":"<div><div>Dual-mode (<em>T₁</em>–<em>T₂</em>) magnetic resonance imaging (MRI) contrast agents offer improved diagnostic capability through simultaneous longitudinal and transverse relaxation enhancement. In this work, quasi-spherical and cubic NiFe₂O₄ nanoparticles were synthesized via a hydrothermal process by varying reaction time and subsequently coated with polyethylene glycol (PEG) to enhance colloidal stability. The quasi-spherical nanoparticles synthesized for 12 h exhibited an average diameter of ∼25 nm and a saturation magnetization (Mₛ) of 49 emu·g<sup>−1</sup>, whereas the cubic nanoparticles obtained after 24 h displayed an edge length of ∼65 nm with Mₛ = ∼ 67 emu·g<sup>−1</sup>. <em>T₁</em>- and <em>T₂</em>-weighted MRI measurements revealed that particle size and surface modification strongly influenced relaxivity. The 25 nm sample showed optimal dual-mode performance, with <em>r₁</em> = 5.7 mM<sup>−1</sup>·s<sup>−1</sup> and <em>r₂</em> = 103.1 mM<sup>−1</sup>·s<sup>−1</sup> (<em>r₂</em>/<em>r₁</em> = ∼18), while PEG coating slightly reduced both relaxivities due to magnetic shielding but significantly improved dispersion stability. 65 nm cubic nanoparticles exhibited high <em>r₂</em> (153.4 mM<sup>−1</sup>·s<sup>−1</sup>), confirming their suitability for <em>T₂</em>-weighted imaging. In vitro MTT cytotoxicity assays on HepG2 cells at 200 μg·mL<sup>−1</sup> demonstrated low toxicity, with cell viability exceeding 80 % after 72 h across all samples and > 94 % for PEG-coated variants. These results demonstrate that controlled morphology and surface engineering of NiFe₂O₄ nanoparticles can effectively tune their magnetic and relaxometric properties, enabling their application as efficient <em>T₁–T₂</em> dual-mode MRI contrast agents.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"639 ","pages":"Article 173786"},"PeriodicalIF":3.0,"publicationDate":"2025-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145881451","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 : 2025-12-24DOI: 10.1016/j.jmmm.2025.173784
C.A.M. Iglesias , S.M. Rezende , J. Xavier , J.H.R. Lima , J.D.M. de Lima , F.L.A. Machado , I.B.T. Silva , M.A. Correa , F. Bohn , J.M. Soares
We report a theoretical approach to describe the magnetoimpedance phenomenon in cylindrical systems at microwave frequencies. Unlike existing theories of giant magnetoimpedance, often linked to the skin-depth effect in magnetic conductors, our theoretical framework is based on a low-loss transmission line model in conjunction with the Landau-Lifshitz-Gilbert equation, applied in systems composed of diamagnetic electrically conductive materials interspersed with magnetic insulating layers. From our proposal, we carry out numerical calculations that yield significant findings, which motivated us to engineer a cylindrical system consisting of a wire and an external layer, both of copper, interspersed by yttrium-iron-garnet powder. The experimental results show remarkable impedance variations on the order of hundreds of ohms at microwave frequencies. In particular, we find a magnetoimpedance variation higher than 4000% at the frequency of 5.27 GHz, which we designate as standing wave shift magnetoimpedance to distinguish this phenomenon from previously recognized effects, since its origin arises from distinct principles.
{"title":"Standing wave shift magnetoimpedance in Cu/YIG/Cu cylindrical system at microwave frequencies","authors":"C.A.M. Iglesias , S.M. Rezende , J. Xavier , J.H.R. Lima , J.D.M. de Lima , F.L.A. Machado , I.B.T. Silva , M.A. Correa , F. Bohn , J.M. Soares","doi":"10.1016/j.jmmm.2025.173784","DOIUrl":"10.1016/j.jmmm.2025.173784","url":null,"abstract":"<div><div>We report a theoretical approach to describe the magnetoimpedance phenomenon in cylindrical systems at microwave frequencies. Unlike existing theories of giant magnetoimpedance, often linked to the skin-depth effect in magnetic conductors, our theoretical framework is based on a low-loss transmission line model in conjunction with the Landau-Lifshitz-Gilbert equation, applied in systems composed of diamagnetic electrically conductive materials interspersed with magnetic insulating layers. From our proposal, we carry out numerical calculations that yield significant findings, which motivated us to engineer a cylindrical system consisting of a wire and an external layer, both of copper, interspersed by yttrium-iron-garnet powder. The experimental results show remarkable impedance variations on the order of hundreds of ohms at microwave frequencies. In particular, we find a magnetoimpedance variation higher than 4000% at the frequency of 5.27 GHz, which we designate as standing wave shift magnetoimpedance to distinguish this phenomenon from previously recognized effects, since its origin arises from distinct principles.</div></div>","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"640 ","pages":"Article 173784"},"PeriodicalIF":3.0,"publicationDate":"2025-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145882786","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 : 2025-12-23DOI: 10.1016/j.jmmm.2025.173782
J.L. Ricardo-Chávez , P. Ajiquichí-Pecher , P. Ruiz-Díaz
<div><div>We present a comprehensive first-principles investigation of the structural, magnetic, and electronic properties of small manganese clusters, Mn<span><math><msub><mrow></mrow><mrow><mi>n</mi></mrow></msub></math></span> (<span><math><mrow><mi>n</mi><mo>≤</mo><mn>7</mn></mrow></math></span>), employing three hybrid density-functional approximations: the range-separated hybrid meta-GGA with nonlocal correlation (<span><math><mi>ω</mi></math></span>B97M-V), the global double-hybrid Becke 2nd-order perturbation with Lee–Yang–Parr correlation (B2PLYP), and the global hybrid Becke three-parameter Lee–Yang–Parr (B3LYP) functionals. Our results demonstrate that the inclusion of nonlocal Hartree–Fock exchange and perturbative correlation critically influences magnetic ordering and bonding, yielding significantly improved agreement with experimental observations compared to semi-local functionals. The structural stability and magnetism of Mn<span><math><msub><mrow></mrow><mrow><mi>n</mi></mrow></msub></math></span> clusters are governed by the localization and splitting of <span><math><mi>d</mi></math></span>-states, as well as the occupancy of the <span><math><mi>s</mi></math></span>-states. For Mn<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>, all three functionals reproduce the experimentally observed weakly bound antiferromagnetic <span><math><mrow><msup><mrow></mrow><mrow><mn>1</mn></mrow></msup><msubsup><mrow><mi>Σ</mi></mrow><mrow><mi>g</mi></mrow><mrow><mo>+</mo></mrow></msubsup></mrow></math></span> ground state. As cluster size increases, the magnetic ground state evolves from ferromagnetic (Mn<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>, Mn<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span>) to ferrimagnetic (Mn<span><math><msub><mrow></mrow><mrow><mn>5</mn></mrow></msub></math></span>–Mn<span><math><msub><mrow></mrow><mrow><mn>7</mn></mrow></msub></math></span>), accompanied by progressive <span><math><mi>d</mi></math></span>-orbital hybridization and partial delocalization. For Mn<span><math><msub><mrow></mrow><mrow><mn>6</mn></mrow></msub></math></span>, both hybrid and double-hybrid functionals predict a bi-capped tetrahedral geometry as the most stable isomer, with <span><math><mi>ω</mi></math></span>B97M-V yielding a ferrimagnetic ground state (<span><math><mrow><mi>μ</mi><mo>=</mo><mn>10</mn><mspace></mspace><msub><mrow><mi>μ</mi></mrow><mrow><mi>B</mi></mrow></msub></mrow></math></span>) reflected in multiple near-degenerate minima. For Mn<span><math><msub><mrow></mrow><mrow><mn>7</mn></mrow></msub></math></span>, the pentagonal bipyramid geometry is consistently stabilized, although <span><math><mi>ω</mi></math></span>B97M-V favors a low-spin ferrimagnetic state (<span><math><mrow><mi>μ</mi><mo>=</mo><mn>5</mn><mspace></mspace><msub><mrow><mi>μ</mi></mrow><mrow><mi>B</mi></mrow></msub></mrow></math></span>), while B2PLYP predicts a high-spin fe
{"title":"Interplay of nonlocal exchange and correlation in the magnetism of small Mn clusters","authors":"J.L. Ricardo-Chávez , P. Ajiquichí-Pecher , P. Ruiz-Díaz","doi":"10.1016/j.jmmm.2025.173782","DOIUrl":"10.1016/j.jmmm.2025.173782","url":null,"abstract":"<div><div>We present a comprehensive first-principles investigation of the structural, magnetic, and electronic properties of small manganese clusters, Mn<span><math><msub><mrow></mrow><mrow><mi>n</mi></mrow></msub></math></span> (<span><math><mrow><mi>n</mi><mo>≤</mo><mn>7</mn></mrow></math></span>), employing three hybrid density-functional approximations: the range-separated hybrid meta-GGA with nonlocal correlation (<span><math><mi>ω</mi></math></span>B97M-V), the global double-hybrid Becke 2nd-order perturbation with Lee–Yang–Parr correlation (B2PLYP), and the global hybrid Becke three-parameter Lee–Yang–Parr (B3LYP) functionals. Our results demonstrate that the inclusion of nonlocal Hartree–Fock exchange and perturbative correlation critically influences magnetic ordering and bonding, yielding significantly improved agreement with experimental observations compared to semi-local functionals. The structural stability and magnetism of Mn<span><math><msub><mrow></mrow><mrow><mi>n</mi></mrow></msub></math></span> clusters are governed by the localization and splitting of <span><math><mi>d</mi></math></span>-states, as well as the occupancy of the <span><math><mi>s</mi></math></span>-states. For Mn<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>, all three functionals reproduce the experimentally observed weakly bound antiferromagnetic <span><math><mrow><msup><mrow></mrow><mrow><mn>1</mn></mrow></msup><msubsup><mrow><mi>Σ</mi></mrow><mrow><mi>g</mi></mrow><mrow><mo>+</mo></mrow></msubsup></mrow></math></span> ground state. As cluster size increases, the magnetic ground state evolves from ferromagnetic (Mn<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>, Mn<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span>) to ferrimagnetic (Mn<span><math><msub><mrow></mrow><mrow><mn>5</mn></mrow></msub></math></span>–Mn<span><math><msub><mrow></mrow><mrow><mn>7</mn></mrow></msub></math></span>), accompanied by progressive <span><math><mi>d</mi></math></span>-orbital hybridization and partial delocalization. For Mn<span><math><msub><mrow></mrow><mrow><mn>6</mn></mrow></msub></math></span>, both hybrid and double-hybrid functionals predict a bi-capped tetrahedral geometry as the most stable isomer, with <span><math><mi>ω</mi></math></span>B97M-V yielding a ferrimagnetic ground state (<span><math><mrow><mi>μ</mi><mo>=</mo><mn>10</mn><mspace></mspace><msub><mrow><mi>μ</mi></mrow><mrow><mi>B</mi></mrow></msub></mrow></math></span>) reflected in multiple near-degenerate minima. For Mn<span><math><msub><mrow></mrow><mrow><mn>7</mn></mrow></msub></math></span>, the pentagonal bipyramid geometry is consistently stabilized, although <span><math><mi>ω</mi></math></span>B97M-V favors a low-spin ferrimagnetic state (<span><math><mrow><mi>μ</mi><mo>=</mo><mn>5</mn><mspace></mspace><msub><mrow><mi>μ</mi></mrow><mrow><mi>B</mi></mrow></msub></mrow></math></span>), while B2PLYP predicts a high-spin fe","PeriodicalId":366,"journal":{"name":"Journal of Magnetism and Magnetic Materials","volume":"639 ","pages":"Article 173782"},"PeriodicalIF":3.0,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145838538","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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