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Exchange spring magnet
About: Exchange spring magnet is a research topic. Over the lifetime, 117 publications have been published within this topic receiving 5056 citations.
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TL;DR: In this article, permanent magnets can be made of composite materials consisting of two suitably dispersed ferromagnetic and mutually exchange-coupled phases, one of which is hard magnetic in order to provide a high coercive field, while the other may be soft magnetic, just providing a high saturation J/sub s/, and should envelop the hard phase regions to prevent their corrosion.
Abstract: It is proposed that permanent magnets can be made of composite materials consisting of two suitably dispersed ferromagnetic and mutually exchange-coupled phases, one of which is hard magnetic in order to provide a high coercive field, while the other may be soft magnetic, just providing a high saturation J/sub s/, and should envelop the hard phase regions in order to prevent their corrosion. A general theoretical treatment of such systems shows that one may expect, besides a high energy product (BH)/sub max/, a reversible demagnetization curve (exchange-spring) and, in certain cases, an unusually high isotropic remanence ratio B/sub r//J/sub s/, while the required volume fraction of the hard phase may be very low, on the order of 10%. The technological realization of such materials is shown to be based on the principle that all phases involved must emerge from a common metastable matrix phase in order to be crystallographically coherent and consequently magnetically exchange coupled. >
2,283 citations
TL;DR: The fabrication of exchange-coupled nanocomposites using nanoparticle self-assembly with an energy product that exceeds the theoretical limit of 13 MG Oe for non-exchange- coupled isotropic FePt by over 50 per cent is reported.
Abstract: Exchange-spring magnets are nanocomposites that are composed of magnetically hard and soft phases that interact by magnetic exchange coupling. Such systems are promising for advanced permanent magnetic applications, as they have a large energy product--the combination of permanent magnet field and magnetization--compared to traditional, single-phase materials. Conventional techniques, including melt-spinning, mechanical milling and sputtering, have been explored to prepare exchange-spring magnets. However, the requirement that both the hard and soft phases are controlled at the nanometre scale, to ensure efficient exchange coupling, has posed significant preparation challenges. Here we report the fabrication of exchange-coupled nanocomposites using nanoparticle self-assembly. In this approach, both FePt and Fe3O4 particles are incorporated as nanometre-scale building blocks into binary assemblies. Subsequent annealing converts the assembly into FePt-Fe3Pt nanocomposites, where FePt is a magnetically hard phase and Fe3Pt a soft phase. An optimum exchange coupling, and therefore an optimum energy product, can be obtained by independently tuning the size and composition of the individual building blocks. We have produced exchange-coupled isotropic FePt-Fe3Pt nanocomposites with an energy product of 20.1 MG Oe, which exceeds the theoretical limit of 13 MG Oe for non-exchange-coupled isotropic FePt by over 50 per cent.
1,483 citations
TL;DR: In this article, the magnetic reversal process in epitaxial Sm-Co bilayer films has been studied and the authors present numerical solutions of a one-dimensional model that provides the spin configuration for each atomic layer.
Abstract: We present results on the magnetic reversal process in epitaxial Sm-Co(11\ifmmode\bar\else\textasciimacron\fi{}00)/TM (TM=Fe,Co) bilayer films prepared via magnetron sputtering. The magnetically hard Sm-Co films have 20-T uniaxial anisotropy and coercivities g3 T at room temperature, that double on cooling, as determined by magnetometry. The TM layers are exchange coupled to the Sm-Co layer and exhibit reversible demagnetization curves expected for an exchange-spring magnet. We also present numerical solutions of a one-dimensional model that provide the spin configuration for each atomic layer. Comparison of the experimental results with the model simulations indicates that our exchange-spring behavior can be understood from the intrinsic parameters of the hard and soft layers. The simulations are extended to realistically estimate the ultimate gain in the energy product that potentially can be realized based on the exchange hardening principle.
404 citations
TL;DR: It is shown that magnetic order can be induced throughout a 40-nm-thick amorphous paramagnetic layer through proximity to ferromagnets, mediating both exchange-spring magnet behaviour and exchange bias.
Abstract: Low-dimensional magnetic heterostructures are a key element of spintronics, where magnetic interactions between different materials often define the functionality of devices. Although some interlayer exchange coupling mechanisms are by now well established, the possibility of direct exchange coupling via proximity-induced magnetization through non-magnetic layers is typically ignored due to the presumed short range of such proximity effects. Here we show that magnetic order can be induced throughout a 40-nm-thick amorphous paramagnetic layer through proximity to ferromagnets, mediating both exchange-spring magnet behaviour and exchange bias. Furthermore, Monte Carlo simulations show that nearest-neighbour magnetic interactions fall short in describing the observed effects and long-range magnetic interactions are needed to capture the extent of the induced magnetization. The results highlight the importance of considering the range of interactions in low-dimensional heterostructures and how magnetic proximity effects can be used to obtain new functionality.
188 citations
TL;DR: In this article, a first-order reversal curve sFORCd technique and vector magnetometry was used to investigate magnetization reversal in exchange-spring magnet films, and it was shown that the switching fields are clearly manifested by separate steps in both longitudinal and transverse hysteresis loops, as well as sharp boundaries in the FORC distribution.
Abstract: Magnetization reversal in exchange-spring magnet films has been investigated by a first-order reversal curve sFORCd technique and vector magnetometry. In Fe/epitaxial-SmCo films, the reversal proceeds by a reversible rotation of the Fe soft layer, followed by an irreversible switching of the SmCo hard layer. The switching fields are clearly manifested by separate steps in both longitudinal and transverse hysteresis loops, as well as sharp boundaries in the FORC distribution. In FeNi/ polycrystalline-FePt films, particularly with thin FeNi, the switching fields are masked by the smooth and step-free major loop. However, the FORC diagram still displays a distinct onset of irreversible switching and transverse hysteresis loops exhibit a pair of peaks, whose amplitude is larger than the maximum possible contribution from the FeNi layer alone. This suggests that the FeNi and FePt layers reverse in a continuous process via a vertical spiral. The successive versus continuous rotation of the soft/hard layer system is primarily due to the different crystal structure of the hard layer, which results in different anisotropies. © 2005 American Institute of Physics . fDOI: 10.1063/1.1954898g
143 citations