Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508375
Zhou, J. Yuan, L. Wei, P. Gan, F. Chen, Y. Zhong, C. Tian, B. Chen, Y. Gao, K. Muramatsu
Abstract
摘要
{"title":"Performance Optimization of a Novel DC Fault Current Limiter Combining Different Magnetic Materials and Topologies.","authors":"Zhou, J. Yuan, L. Wei, P. Gan, F. Chen, Y. Zhong, C. Tian, B. Chen, Y. Gao, K. Muramatsu","doi":"10.1109/INTMAG.2018.8508375","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508375","url":null,"abstract":"Abstract","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"1 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75939179","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508343
K. O’Grady, G. Vallejo-Fernandez
The characterisation of antiferromagnets (AFs) for almost all applications is very challenging because intrinsically an AF gives little or no signal. Above the Néel temperature (TN) AF materials exhibit paramagnetic behaviour in a similar manner to a ferromagnet above its Curie point. This does allow for the determination of the Néel temperature but reveals little about the behaviour of the material once the AF order is established. Historically the structure of AFs was determined using techniques such as neutron scattering [1], [2] and more recently some studies have been undertaken using X-ray techniques such as XMCD [3]. However such techniques and particularly neutron scattering require large samples with dimensions of the order of millimetres. For all technological applications AF materials are used in thin film form and hence such techniques are not available for use due to the very long counting times that would be required. A second problem with AF materials is that their behaviour has not been well established until recently. For example Néel predicted the existence of AF domains but there are very few reports of their observation [4], [5]. Their behaviour is not well understood because conventional domain theory is based around the existence of magnetostatic energy in a conventional ferromagnet which is not present in an AF. Other critical factors associated with the structure of thin films are also poorly understood. Principal amongst these is that in polycrystalline films a granular structure will exist but the question then arises as to at what critical grain size will single domain behaviour be observed? In single crystal or large grain thin films where presumably AF domains will form, what is the nature and consequence of domain wall pinning? In this tutorial lecture the fundamental nature of antiferromagnets will be discussed addressing metals, alloys and oxides. However the focus will be on those materials which have, or are most likely to find application in spintronic devices. Techniques that allow the behaviour of AF thin films at least to be inferred will also be discussed. These are principally associated with the measurement of exchange bias systems where a ferromagnetic layer is used as an indicator of the structure of an underlying AF. However in exchange bias systems it is also the case that the exchange field from the ferromagnet causes a reaction and possibly a change of order in the AF. This concept is the basis of the so-called York Protocols which allow for the measurement of the behaviour of granular, generally sputtered, AF films. The underlying York Model of Exchange Bias developed in 2008 will then be discussed in detail as it allows for the full characterisation of granular films and in particular the determination of the anisotropy constant of AFs. This model has been used by all the major manufacturers of hard drive read heads to design improved AF layers in their stacks. For the case of large grain or single
{"title":"Characterisation of Antiferromagnets","authors":"K. O’Grady, G. Vallejo-Fernandez","doi":"10.1109/INTMAG.2018.8508343","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508343","url":null,"abstract":"The characterisation of antiferromagnets (AFs) for almost all applications is very challenging because intrinsically an AF gives little or no signal. Above the Néel temperature (TN) AF materials exhibit paramagnetic behaviour in a similar manner to a ferromagnet above its Curie point. This does allow for the determination of the Néel temperature but reveals little about the behaviour of the material once the AF order is established. Historically the structure of AFs was determined using techniques such as neutron scattering [1], [2] and more recently some studies have been undertaken using X-ray techniques such as XMCD [3]. However such techniques and particularly neutron scattering require large samples with dimensions of the order of millimetres. For all technological applications AF materials are used in thin film form and hence such techniques are not available for use due to the very long counting times that would be required. A second problem with AF materials is that their behaviour has not been well established until recently. For example Néel predicted the existence of AF domains but there are very few reports of their observation [4], [5]. Their behaviour is not well understood because conventional domain theory is based around the existence of magnetostatic energy in a conventional ferromagnet which is not present in an AF. Other critical factors associated with the structure of thin films are also poorly understood. Principal amongst these is that in polycrystalline films a granular structure will exist but the question then arises as to at what critical grain size will single domain behaviour be observed? In single crystal or large grain thin films where presumably AF domains will form, what is the nature and consequence of domain wall pinning? In this tutorial lecture the fundamental nature of antiferromagnets will be discussed addressing metals, alloys and oxides. However the focus will be on those materials which have, or are most likely to find application in spintronic devices. Techniques that allow the behaviour of AF thin films at least to be inferred will also be discussed. These are principally associated with the measurement of exchange bias systems where a ferromagnetic layer is used as an indicator of the structure of an underlying AF. However in exchange bias systems it is also the case that the exchange field from the ferromagnet causes a reaction and possibly a change of order in the AF. This concept is the basis of the so-called York Protocols which allow for the measurement of the behaviour of granular, generally sputtered, AF films. The underlying York Model of Exchange Bias developed in 2008 will then be discussed in detail as it allows for the full characterisation of granular films and in particular the determination of the anisotropy constant of AFs. This model has been used by all the major manufacturers of hard drive read heads to design improved AF layers in their stacks. For the case of large grain or single","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"5 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75086420","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508483
N. Taran, D. Ionel, D. Dorrel
Many parameters are considered in electric machine design and an optimization algorithm can be used. These usually need thousands of design evaluations before meeting the termination criterion. Time consuming 3D finite element analyses (FEAs) are not tenable although machines with 3D flux paths, such as axial flux and transverse flux, cannot be accurately evaluated with 2D models. One solution is to use surrogate models rather than 3D FEA; however, the accuracy of surrogate models reduces for a large and nonlinear search space. Another solution can utilize algorithms that find the global optima with a minimum number of design evaluations. A combination of these two solutions is proposed here.
{"title":"Two-Level Surrogate-Assisted Differential Evolution Multi-ob-jective Optimization of Electric Machines Using 3D Finite Element Analysis (FEA).","authors":"N. Taran, D. Ionel, D. Dorrel","doi":"10.1109/INTMAG.2018.8508483","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508483","url":null,"abstract":"Many parameters are considered in electric machine design and an optimization algorithm can be used. These usually need thousands of design evaluations before meeting the termination criterion. Time consuming 3D finite element analyses (FEAs) are not tenable although machines with 3D flux paths, such as axial flux and transverse flux, cannot be accurately evaluated with 2D models. One solution is to use surrogate models rather than 3D FEA; however, the accuracy of surrogate models reduces for a large and nonlinear search space. Another solution can utilize algorithms that find the global optima with a minimum number of design evaluations. A combination of these two solutions is proposed here.","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"95 1","pages":"1-2"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74947880","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508430
X. Zhao, H. Zhang, L. Li, F. Xiao, X. Liu, Yachao Li
Two dimensional (2-D) magnetic flux exist in rotating electric machines and T-joints of three-phase power transformers and may cause local overheating in these devices. The soft magnetic materials, such as electrical steel sheet and soft magnetic composite (SMC), are usually used in the fabrication process of ferromagnetic core. Therefore, it has been focus of attentions to measure and model 2-D magnetic properties of soft magnetic materials in recent years [1], [2]. Compared with the Stoner-Wohlfarth hysteresis model, the Preisach model has the advantage over parameter identification and numerical implementation, and it has been widely used in modeling 2-D vector hysteretic characteristics. Due to the defects of classical vector Preisach model, simulation cannot agree well with measurement, therefore it is necessary to improve the classical vector model. In this paper, by introducing the function $z$, the classical Preisach model is improved to model the 2-D vector hysteresis of SMC considering the influence of anisotropy, the simulated results by the improved model is coincided with the measured ones. The proposed method is meaningful for exploring the rotating magnetic and loss characteristics of electric motor and power transformer.
{"title":"Vector Hysteresis Modeling of Soft Magnetic Composite by the Improved Preisach Model Considering Anisotropic Characteristic.","authors":"X. Zhao, H. Zhang, L. Li, F. Xiao, X. Liu, Yachao Li","doi":"10.1109/INTMAG.2018.8508430","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508430","url":null,"abstract":"Two dimensional (2-D) magnetic flux exist in rotating electric machines and T-joints of three-phase power transformers and may cause local overheating in these devices. The soft magnetic materials, such as electrical steel sheet and soft magnetic composite (SMC), are usually used in the fabrication process of ferromagnetic core. Therefore, it has been focus of attentions to measure and model 2-D magnetic properties of soft magnetic materials in recent years [1], [2]. Compared with the Stoner-Wohlfarth hysteresis model, the Preisach model has the advantage over parameter identification and numerical implementation, and it has been widely used in modeling 2-D vector hysteretic characteristics. Due to the defects of classical vector Preisach model, simulation cannot agree well with measurement, therefore it is necessary to improve the classical vector model. In this paper, by introducing the function $z$, the classical Preisach model is improved to model the 2-D vector hysteresis of SMC considering the influence of anisotropy, the simulated results by the improved model is coincided with the measured ones. The proposed method is meaningful for exploring the rotating magnetic and loss characteristics of electric motor and power transformer.","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"76 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77396089","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508144
M. Nilges, P. Schegner
Voltage stress due to steep impulses during switching operations of e.g. vacuum circuit breakers and ongoing harmonics caused by converters are a well-known but still increasing problem in the field of transformer design and operation [1]. In order to investigate the behavior of transformers during such impulses and oscillations, several models have been developed [2,3]. However, with increasing complexity of the coils, all studies show minor to major deviations in computation, compared to the corresponding measurements. Due to a high number of turns in the high voltage coils of transformers, the errors caused by simplifications or inaccurate data of the interwinding geometry can be tremendous. Hence, it is necessary to know which parameters are influencing the resonance behavior significantly and need to be represented accurately, while other parameters may be neglected. Therefore, a parameter study has been carried out, in order to analyze the resonance behavior of a simple coil geometry, based on FEM computations.
{"title":"Influence of the Winding Geometry and its Materials on the Resonance Behavior of Transformer Coils","authors":"M. Nilges, P. Schegner","doi":"10.1109/INTMAG.2018.8508144","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508144","url":null,"abstract":"Voltage stress due to steep impulses during switching operations of e.g. vacuum circuit breakers and ongoing harmonics caused by converters are a well-known but still increasing problem in the field of transformer design and operation [1]. In order to investigate the behavior of transformers during such impulses and oscillations, several models have been developed [2,3]. However, with increasing complexity of the coils, all studies show minor to major deviations in computation, compared to the corresponding measurements. Due to a high number of turns in the high voltage coils of transformers, the errors caused by simplifications or inaccurate data of the interwinding geometry can be tremendous. Hence, it is necessary to know which parameters are influencing the resonance behavior significantly and need to be represented accurately, while other parameters may be neglected. Therefore, a parameter study has been carried out, in order to analyze the resonance behavior of a simple coil geometry, based on FEM computations.","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"52 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80414091","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/intmag.2018.8508542
S. Wang, J. Luo
Extensive experiments have been devoted to study the deterministic switching of perpendicularly magnetized layers in heavy metal/ferromagnet devices driven by spin orbital torque by the spin Hall effect [1–4]. A perpendicular magnetized layer has been proved to be successfully and deterministically switched under certain circumstances experimentally and theoretically [5–8]. To obtain high perpendicular anisotropy, the thickness of the film needs to be sufficiently small (<1 nm). To resist the thermal fluctuations during operation, we proposed a multilayer structure including exchange-coupled perpendicularly magnetized layers to switch at relatively low currents and maintain thermal stability, inspired by the ECC media in HDD systems [9]. Without loss of generality, we simply used an in-plane field along the charge current direction (y) to describe the effective field to break the symmetry of rotation in response to the spin orbital torque in our simulation. Fig.1(a) illustrates our design: the bottom magnetic layer is softer $(K_{1} < K_{2})$ and is relatively vulnerable to the reversal torque. We used typical magnetic parameters for each layer: the saturation magnetization $M_{s1}=1200$ emu/cm3 and $M_{s2}=800$ emu/cm3, and the effective anisotropy constants $K_{1}= 0.5 times 10 ^{6}$ erg/cm3 and $K_{2}= 2 times 10 ^{6}$ erg/cm3. We assume only the bottom magnetic layer is subject to the spin orbital torque as the torque originates from spin orbit interaction. Without any applied currents the multilayer relaxes to its equilibrium state and the average magnetization is slightly tilted towards y axis (about 12°). In the switching process, the softer magnetic layer tends to reverse first and the harder layer follows driven by the exchange interaction. The critical spin current density is 5MA/cm2. Our new structure provides a way to design and optimize the spintronic device.
{"title":"Switching of Exchange-Coupled Perpendicular Magnetized Layers Driven by Spin Orbital Torque With Low Power Consumption","authors":"S. Wang, J. Luo","doi":"10.1109/intmag.2018.8508542","DOIUrl":"https://doi.org/10.1109/intmag.2018.8508542","url":null,"abstract":"Extensive experiments have been devoted to study the deterministic switching of perpendicularly magnetized layers in heavy metal/ferromagnet devices driven by spin orbital torque by the spin Hall effect [1–4]. A perpendicular magnetized layer has been proved to be successfully and deterministically switched under certain circumstances experimentally and theoretically [5–8]. To obtain high perpendicular anisotropy, the thickness of the film needs to be sufficiently small (<1 nm). To resist the thermal fluctuations during operation, we proposed a multilayer structure including exchange-coupled perpendicularly magnetized layers to switch at relatively low currents and maintain thermal stability, inspired by the ECC media in HDD systems [9]. Without loss of generality, we simply used an in-plane field along the charge current direction (y) to describe the effective field to break the symmetry of rotation in response to the spin orbital torque in our simulation. Fig.1(a) illustrates our design: the bottom magnetic layer is softer $(K_{1} < K_{2})$ and is relatively vulnerable to the reversal torque. We used typical magnetic parameters for each layer: the saturation magnetization $M_{s1}=1200$ emu/cm3 and $M_{s2}=800$ emu/cm3, and the effective anisotropy constants $K_{1}= 0.5 times 10 ^{6}$ erg/cm3 and $K_{2}= 2 times 10 ^{6}$ erg/cm3. We assume only the bottom magnetic layer is subject to the spin orbital torque as the torque originates from spin orbit interaction. Without any applied currents the multilayer relaxes to its equilibrium state and the average magnetization is slightly tilted towards y axis (about 12°). In the switching process, the softer magnetic layer tends to reverse first and the harder layer follows driven by the exchange interaction. The critical spin current density is 5MA/cm2. Our new structure provides a way to design and optimize the spintronic device.","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"4 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80502941","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508153
S. Iemoto, S. Sumi, H. Awano, M. Hayashi
Magnetic film with a heavy metal layer shows strong interfacial interaction of spin-orbit. Spin-orbit interaction (SOI) is one of the key technologies for spintronics and its applications. It is important to reveal the SOI [1]. On the other hand, it is known that magneto-optical Kerr effect is a useful method to detect interfacial information, especially using interference [2], [3]. There are many reports about magneto-optical Kerr effect in a rear earth transition metal (RE-TM) film with a noble metal layer such as Pt, Pd, etc [4], [5]. However, there are few reports about discussion on the SOI. In this paper, we measured magneto-optical Kerr spectrums of Pt/TbCo heterostructure films, and discuss about contribution of the SOI.
{"title":"Magneto-optical properties of Pt/TbCo heterostructure films.","authors":"S. Iemoto, S. Sumi, H. Awano, M. Hayashi","doi":"10.1109/INTMAG.2018.8508153","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508153","url":null,"abstract":"Magnetic film with a heavy metal layer shows strong interfacial interaction of spin-orbit. Spin-orbit interaction (SOI) is one of the key technologies for spintronics and its applications. It is important to reveal the SOI [1]. On the other hand, it is known that magneto-optical Kerr effect is a useful method to detect interfacial information, especially using interference [2], [3]. There are many reports about magneto-optical Kerr effect in a rear earth transition metal (RE-TM) film with a noble metal layer such as Pt, Pd, etc [4], [5]. However, there are few reports about discussion on the SOI. In this paper, we measured magneto-optical Kerr spectrums of Pt/TbCo heterostructure films, and discuss about contribution of the SOI.","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"72 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85491031","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508108
A. Smekhova, E. L. Torre, T. Szyjka, B. Eggert, B. Cöster, K. Ollefs, D. Walecki, S. Salamon, R. Bali, J. Lindner, F. Wilhelm, A. Rogalev, E. Weschke, D. Többens, R. Banerjee, B. Sanyal, C. Schmitz-Antoniak, H. Wende
Thin films of Fe-rich transition metal aluminide Fe60Al40 (at. %) are very promising for implementation in modern technology due to a possibility of having tailored magnetic properties. Being weakly ferromagnetic at room temperature in the chemically ordered B2 phase, Fe60Al40 films can be reversibly transformed into the ferromagnetic chemically disordered A2 phase with much higher magnetization in a well controlled way by means of ion irradiation. Prior studies point on important influence of created chemical disorder on static and dynamic magnetic properties of Fe60Al40 films while achievements in magnetic patterning and studies of magnetization reversal have shown their perspective for further use in spin-transport devices [1–3]. Detailed studies performed on a local scale can clarify hidden mechanisms of disorder induced ferromagnetism phenomena in Fe60Al40 films via understanding the influence of the local surrounding and features of Fe-Al hybridization on the magnetic properties. In our work, element-specific X-ray absorption spectroscopy (EXAFS, XANES, and XMCD) in hard-and soft energy ranges together with synchrotron-based XRD (SR-XRD) have been applied to probe the local rearrangements and related magnetic and electronic properties of Fe and Al atoms in bare Fe60Al40 thin films of 40 nm thickness through the order-disorder $( mathrm {B}2 rightarrow {A}2$) phase transition initiated by 20keV Ne+ ion irradiation with low fluences ~1014 ions cm-2). Extended X-ray absorption fine structure (EXAFS) spectra recorded at the Fe and Al K edges at room temperature (RT) and low temperature of 5K (LT) and SR-XRD have shown significant changes in the local environment of Fe and Al absorbers before and after the irradiation. In the course of the transition a number of Fe-Fe nearest-neighbors grew from 3.47(7) up to 5.0(1) for the ordered B2 and the fully disordered A2 phases, correspondingly, and ~1% of the unit cell volume expansion was found. Distinct changes of Fe and Al coordination due to disordering resulted in increased Fe 3d spin and 4p orbital polarizations and characteristic changes in electronic structure of Al atoms as was demonstrated by RT XMCD at the Fe L2,3 and Fe K edges as well as LT XANES at the Al K edge, respectively [4, 5]. A unique possibility to probe the magnetism of 3d states by hard X-rays has been realized by recording the XMCD signal at ~60 eV above the Fe K edge where so-called magnetic multi-electronic excitations (MEE, secondary processes) are present [6, 7]. The analysis of MEE peak amplitude and its integrated intensity has revealed similar tendencies in their changes with fluence as for 3d effective spin and 3d orbital magnetic moments obtained from XMCD spectra at the Fe L2,3 edges, respectively. Moreover, this analysis points towards increased localization of Fe 3d states in A2 phases created by fluencies of (0.75-6) × 1014 ions cm-2. Element-specific hysteresis loops (ESHL) recorded by XMCD either at the Fe K or L
{"title":"Peculiarities of Disorder-Induced Ferromagnetism Phenomena in Fe60A40 films on a local scale.","authors":"A. Smekhova, E. L. Torre, T. Szyjka, B. Eggert, B. Cöster, K. Ollefs, D. Walecki, S. Salamon, R. Bali, J. Lindner, F. Wilhelm, A. Rogalev, E. Weschke, D. Többens, R. Banerjee, B. Sanyal, C. Schmitz-Antoniak, H. Wende","doi":"10.1109/INTMAG.2018.8508108","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508108","url":null,"abstract":"Thin films of Fe-rich transition metal aluminide Fe60Al40 (at. %) are very promising for implementation in modern technology due to a possibility of having tailored magnetic properties. Being weakly ferromagnetic at room temperature in the chemically ordered B2 phase, Fe60Al40 films can be reversibly transformed into the ferromagnetic chemically disordered A2 phase with much higher magnetization in a well controlled way by means of ion irradiation. Prior studies point on important influence of created chemical disorder on static and dynamic magnetic properties of Fe60Al40 films while achievements in magnetic patterning and studies of magnetization reversal have shown their perspective for further use in spin-transport devices [1–3]. Detailed studies performed on a local scale can clarify hidden mechanisms of disorder induced ferromagnetism phenomena in Fe60Al40 films via understanding the influence of the local surrounding and features of Fe-Al hybridization on the magnetic properties. In our work, element-specific X-ray absorption spectroscopy (EXAFS, XANES, and XMCD) in hard-and soft energy ranges together with synchrotron-based XRD (SR-XRD) have been applied to probe the local rearrangements and related magnetic and electronic properties of Fe and Al atoms in bare Fe60Al40 thin films of 40 nm thickness through the order-disorder $( mathrm {B}2 rightarrow {A}2$) phase transition initiated by 20keV Ne+ ion irradiation with low fluences ~1014 ions cm-2). Extended X-ray absorption fine structure (EXAFS) spectra recorded at the Fe and Al K edges at room temperature (RT) and low temperature of 5K (LT) and SR-XRD have shown significant changes in the local environment of Fe and Al absorbers before and after the irradiation. In the course of the transition a number of Fe-Fe nearest-neighbors grew from 3.47(7) up to 5.0(1) for the ordered B2 and the fully disordered A2 phases, correspondingly, and ~1% of the unit cell volume expansion was found. Distinct changes of Fe and Al coordination due to disordering resulted in increased Fe 3d spin and 4p orbital polarizations and characteristic changes in electronic structure of Al atoms as was demonstrated by RT XMCD at the Fe L2,3 and Fe K edges as well as LT XANES at the Al K edge, respectively [4, 5]. A unique possibility to probe the magnetism of 3d states by hard X-rays has been realized by recording the XMCD signal at ~60 eV above the Fe K edge where so-called magnetic multi-electronic excitations (MEE, secondary processes) are present [6, 7]. The analysis of MEE peak amplitude and its integrated intensity has revealed similar tendencies in their changes with fluence as for 3d effective spin and 3d orbital magnetic moments obtained from XMCD spectra at the Fe L2,3 edges, respectively. Moreover, this analysis points towards increased localization of Fe 3d states in A2 phases created by fluencies of (0.75-6) × 1014 ions cm-2. Element-specific hysteresis loops (ESHL) recorded by XMCD either at the Fe K or L","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"39 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85516838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508501
M. d’Aquino, C. Serpico, V. Scalera
Magnetization switching in nanoparticles and thin-films is the fundamental issue to deal with in order to obtain high speed and energy-efficient recording devices [1]. The optimization of switching mechanisms is constrained in the framework of the so-called magnetic recording trilemma. On one hand, one would like to have the magnetized bit occupying a smaller area on the recording medium and, at the same time, magnetization remaining stable over long enough time for reliable data retention. These two constraints are competing since thermal stability decreases with decreasing active volume of the magnetic bit. On the other hand, circumventing this issue would require higher coercivity of the magnetic material and, consequently, larger current feeding the write head. However, the maximum current amplitude is constrained by technological limits in the realizations of the pole tips and, thus, one cannot meet the aforementioned requirements. For these reasons, several strategies have been investigated in the last decades to realize fast magnetization switching with greater efficiency, such as microwave-assisted switching [2] and precessional switching [3]. In particular, the latter occurs through the application of a field transverse to the initial magnetization and yields much smaller switching times than conventional switching [4], [5]. However, to achieve successful switching, an extremely precise design of the field pulse is needed to switch off the field at the right moment [6]. Then, the equilibrium magnetization is reached after a relaxation from a high-to low-energy state [7]. This mechanism is probabilistic even when thermal fluctuations are neglected, due to multistability and small dissipation in magnetization dynamics [8]. When also thermal fluctuations are considered, the stochasticity of the switching process is even more pronounced [3]. On the other hand, magnetic recording devices must undergo strict reliability requirements in terms of extremely low write-error rates, which can be realized at expense of the speed of the write process. In this paper, we theoretically analyze the magnetization switching for a single magnetic grain of the recording medium subject to the write head field pulses and room temperature thermal fluctuations, as it is the case of perpendicular magnetic recording. This situation, in the absence of thermal fluctuations and for special symmetry of the magnetic particle, has been studied in a pioneering paper [9] and is referred to as damping switching. In this paper, by using analytical techniques, we derive expressions for the switching times distribution functions in terms of material, geometrical and external field properties. These analytical results provide a tool to quantify the write-error rates as function of design parameters, which may help the optimization of switching processes. To this end, we consider the Landau-Lifshitz-Gilbert (LLG) equation augmented with a thermal field of stochastic nature [10],
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Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508850
M. Goiriena-Goikoetxea, I. Orue, K. Guslienko, E. Berganza, M. Jaafar, A. Asenjo, D. Muñoz, A. Muela, A. García-Arribas
Magnetic dots in vortex state have been intensively studied due to their attractive properties for emerging multidisciplinary applications such as magnetic information storage, spintronics and biomedicine. In the vortex ground state, the magnetic moments are curled in the dot plane and only at the center the core of the vortex points perpendicularly to the plane. This configuration gives rise to a characteristic magnetic behavior as a function of the in-plane applied magnetic field, displaying hysteresis loops with no remanence or coercive field and open lobes at high field [1]. Apart from the intrinsic interest that this peculiar magnetic structure offers from a fundamental point of view, some appealing applications for this type of particles have been proposed, such as the magneto-mechanical actuation for cancer cell destruction [2]. This therapy employs disc-shaped particles with vortex magnetic configuration that, under an low amplitude (about 10 mT) and low frequency (tens of Hertz) AC fields, are made to oscillate, hitting and damaging the integrity of cancer cells to which they were attached. Since this actuation does not imply heat generation, in principle, the magneto-mechanical actuation avoids the risk of damaging the surrounding healthy tissue as it can occur in magnetic hyperthermia. Additionally, it is thought that the magneto-mechanical actuation leads to the apoptosis of the cells instead of the necrotic pathway caused by heating, avoiding cell-leakage in the surrounding extracellular environment and inflammatory reactions caused by necrosis [3]. In this work, we present the results obtained in Permalloy circular dots fabricated by hole mask colloidal lithography (HCL) with diameters ranging from 60 to 140 nm, and different thicknesses from 20 to 60 nm. HCL is a bottom-up fabrication technique that basically uses a monolayer of self-assembled polystyrene nanospheres to create a template of holes in a polymer film deposited over a substrate. The holes are filled with sputtered Permalloy and the polymeric template removed to produce a dense pattern of dots on the substrate [4]. For their use in the in vitro experiments, the nanostructures are prepared on top of a sacrificial layer that is later removed to release the discs. In this case, the discs are prepared with a thin (4 nm) gold layer on both sides. The nanodiscs on the substrate are magnetically characterized by SQUID and MOKE magnetometries, and Magnetic Force Microscopy (MFM). Additional micromagnetic simulations and analytic calculations have been performed to clarify the magnetization configuration in the dots with different diameter to thickness ratios [5]. In the dots with a diameter of 140 nm, the MFM images reveal that the vortex core occupies about half the size of the dots. This vortex core diameter is approximately equal to the dot diameter for the smaller dots (60 nm). Micromagnetic calculations confirms that, in this case, the size of the core can be even greater
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