Valence Fluctuation in Amorphous Alloys, and Magnetic and Electrical Properties

Fe_2Ce非晶合金的居里温度低于deGennes因子的预期值，其磁矩小于Fe_2Zr非晶合金。这些结果表明，Ce原子成为四价态的Fe由于价态波动。X射线衍射分析表明，Fe_2Ce非晶合金的配位数和原子间距与其它Fe_22R（R：稀土金属）非晶合金有很大的不同。通过吸氢实验，观察到这些化合物的结构和磁性发生了剧烈的变化。除Fe_2Ce外，Fe_2R非晶合金的室温密度与稀土金属的室温密度呈线性关系。室温密度的浓度依赖性是奇怪的。也就是说，虽然Ce的密度小于Fe的密度，但随着Ce含量从10%增加到35%，密度略有增加。这意味着这个系统不服从 ...更多信息 Vegard定律。这些结果也解释了考虑Ce的价态涨落。稀有金属具有极大的自旋-轨道角动量和大的随机轴向各向异性观察到在非晶态。Fe-R非晶合金在低温下具有很大的矫顽力是由其随机轴向各向异性引起的。而在Fe_2Ce非晶合金中没有观察到如此大的矫顽力。这一现象可以用Ce的价态变化来解释，因为Ce在四价态时没有磁矩，也没有随机轴向各向异性，从而得出Fe-Ce非晶合金是典型的价态涨落材料的结论。由于非晶态合金的随机性，电子的平均自由程很短，电阻率比晶体高出一到两个数量级。因此，可以认为化合价涨落对电阻率的影响并不显著。少

The Curie temperature of Fe_2Ce amorphous alloys is lower than the value expected from the deGennes factor and its magnetic moment is smaller than that of Fe_2Zr amorphous alloy. These results suggest that Ce atoms become the tetravalent state in Fe due to the valence fluctuation. The X-ray diffraction analysis revealed that the coordination number and the atomic distance of Fe_2Ce amorphous alloy are very different from those of other Fe_22R(R:rare earth metal) amorphous alloys. By hydrogen absorption, the drastic changes of these structure and magnetic properties were observed. The linear relationship between the room temperature density of Fe_2R amorphous alloys and it of rare earth metals was confirmed, except for the value of Fe_2Ce. The concentration dependence of room temperature density is strange. That is, the density slightly increases with increasing the Ce content from 10% to 35% though the density of Ce is smaller than that of Fe. The means that this system does not obeys … More Vegard's law. These results are also explained by considering the valence fluctuation of Ce.Rare metals have a extremely large spin-orbital angular momentum and a large random axial anisotropy is observed in the amorphous state. The huge coercive force at low temperatures for Fe-R amorphous alloys is caused by the random axial anisotropy. However, such a large coercive force is not observed in Fe_2Ce amorphous alloys. This fact is explained by the change of valence of Ce, because Ce in the tetravalent state has no magnetic moment accompanying the no random axial anisotropy.From these results mentioned above, it is concluded that Fe-Ce amorphous allys are typical materials in fluctuating valence state. The mean free path of electrons in amorphous alloys is very short due to the randomness and the electrical resistivity is higher than the value of crystals by one or two orders of magnitude. Therefore, it is considered that the effect of the valence fluctuation on the electrical resistivity is apparently not so remarkable. Less