Magneto-volume Effects in Fe-based Amorphous Alloys

研究了压力对具有大磁体积效应的铁基非晶合金居里温度和磁化强度的影响。当Fe浓度很高时，合金的磁化曲线不遵循1/H趋近饱和的规律，而是遵循1/H^<1/2>的规律。后一幂律对具有反磁相互作用的合金体系是有效的。值得注意的是，随机轴向磁各向异性合金体系的曲线并不遵循1/H^<1/2>定律。研究了线性和强制体积磁致伸缩对温度和场的依赖关系。这两个值都非常大，在自旋冻结和居里温度下，强迫体积磁摩擦表现出发散的趋势。这些结果与局域系统的结果有很大的不同。fe - fe非晶合金的加氢引起了磁化强度的急剧增加。由于随机磁各向异性，如果通过氢化将Ce的价由四价还原为三价，我们可以预期在低温下具有巨大的矫顽力。然而，没有这么大的矫顽力被证实。这种行为可以解释为氢原子聚集在Ce原子周围，导致电子结构改变。因此，我们不能把氢化引起的体积膨胀假定为负压。非晶Y-Fe合金退火后磁性能的变化与Fe-Fe对原子间距离和Fe原子配位数的增加有关。

The pressure effects on the Curie temperature and magnetization for Fe-based amorphous alloys which have large magnetovolume effects have been investigated. The magnetization curves for the alloys with a very high concentration of Fe do not follow the law of approach to saturation with 1/H but follow that with 1/H^<1/2>. The latter power law is valid for the alloy systems which have antifferomagnetic interactions. It should be noted that the curves for random axial magnetic anisotropy alloy systems do not follow the 1/H^<1/2> law.The temperature and field dependences of linear and forced volume magnetostrictions have been investigated. These two values are markedly large and the forced-volume magnetosriction exhibits a tendency to diverge at the spin freezing and the Curie temperatures. These results are very different from those for the localized systems.The dramatic increase in the magnetization is caused by hydrogenation for Ce-Fe amorphous alloys. We can expect a huge coercivity at low temperatures due to the random magnetic anisotropy if the valence of Ce is reduce from tetravalent to trivalent by hydrogenation. However no such a large coercivity has been confirmed. This behavior is explained by the aggregation of hydrogen atoms around Ce atoms, resulting in the altered electronic structure. Therefore, we can not assume that the expansion of volume by hydrogenation as the negative pressure.The changes in the magnetic properties by annealing for amorphous Y-Fe alloys are correlated to the increases in the interatomic distance of Fe-Fe pairs and the coordination numbers of Fe atoms.