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首页> 外文期刊>Journal of Experimental and Theoretical Physics >Theoretical Prediction of a Surface-Induced Spin-Reorientation Phase Transition in BaFe_(12)O_(19) Nanocrystals
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Theoretical Prediction of a Surface-Induced Spin-Reorientation Phase Transition in BaFe_(12)O_(19) Nanocrystals

机译：BaFe_（12）O_（19）纳米晶体中表面诱导的自旋取向相变的理论预测

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The equation of the magnetization of a hexagonal crystal is derived for the first time for an arbitrary orientation of the external magnetic field relative to the crystallographic c axis. IN order to clarify the magnetization mechanism for a real ensemble of small particles in the framework of the given problem, surface anisotropy (which is significant for nanosize objects) was taken into account along with crystalline magnetic anisotropy and anisotropy in the particle shape. Model computer experiments prove that the magnetization curves for nanocrystals oriented in a polar angle range of 65-90 ° exhibit an anomaly in the form of a jump, indicating a first-order spin-reorientation phase transition. This explains a larger steepness of the experimental curve reconstructed taking into account the interaction between particles as compared to the theoretical curve reconstructed taking into account the interaction between particles as compared to the theoretical dependence obtained by Stoner and Wohlfarth [IEEE Trans. Magn. MAG 27 (4), 3469 (1991)]. An analysis of variation of the characteristic anisotropy surface and its cross section with increasing ratio |K_2|/K_1 of the crystalline magnetic anisotropy constants upon a transition from a macroscopic to a nanoscopic crystal shows that surface anisotropy leads to a change in the magnetic structure. As a result, an additional easy magnetization direction emerges in the basal plane apart from the easiest magnetization direction (along the c axis). The direction of hard magnetization emerges from the basal plane, the angle of its orientation relative to the c axis being a function of the ratio |K_2|/K_1.
机译：对于外部磁场相对于晶体学c轴的任意取向，首次导出了六方晶的磁化方程。为了在给定问题的框架内阐明小颗粒的真实整体的磁化机理，将表面各向异性（对于纳米尺寸的物体而言很重要）与晶体磁各向异性和颗粒形状的各向异性一起考虑在内。模型计算机实验证明，在65-90°极角范围内取向的纳米晶体的磁化曲线表现出跳跃形式的异常，表明一阶自旋取向相变。这解释了重构的实验曲线的陡度要比与Stoner和Wohlfarth [IEEE Trans。真是的MAG 27（4），3469（1991）]。当从宏观晶体向纳米晶体转变时，特征各向异性表面及其横截面随晶体磁各向异性常数的比率| K_2 | / K_1的增大而变化的分析表明，表面各向异性导致磁结构的变化。结果，除了最容易的磁化方向（沿着c轴）之外，在基面上出现了另外的容易的磁化方向。硬磁化方向从基面出现，其方向相对于c轴的角度是比率| K_2 | / K_1的函数。

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