Theoretical Investigations of Structure vs Magnetism in Amorphous Alloys Showing Anomalous Magnetic Behaviors

我们在泛函积分方法的基础上，将描述局域磁矩随机分布的分布函数方法与用于非晶态合金电子结构计算的几何平均模型相结合，发展了非晶态磁性合金的有限温度理论。将我们的理论应用于铁磁性被结构无序破坏的非晶态Fe-Zr合金和结构无序增强了铁磁性的非晶态Co-Y合金，阐明了结构无序对其电子结构和各种磁性的影响。接下来，我们将这一理论应用于表现出特殊磁性的非晶态Tm-Y(Tm=Mn，Fe，Co，Ni)合金，结果表明，最随机的原子组态解释了它们的磁相图的总体特征，如在Mn-Y中出现自旋玻璃(SG)，在快凝Fe-Y中出现SG-F(铁磁性)-P(顺磁性)相变，以及在Co-Y和Ni-Y合金…中发生F-P相变更多。该理论还半定量地解释了磁化强度和磁化率对浓度和温度的依赖关系。这些磁性是由Mn局域磁矩(Mn-Y)之间的反铁磁耦合、磁矩的局域环境效应和Fe局域磁矩(Fe-Y)、原子尺寸效应(Fe-Y和Co-Y)以及3D-4d杂化(Co-Y和Ni-Y)之间的非线性磁耦合引起的。我们还考察了原子短程有序对Fe-Y的影响，发现F-SG转变是随着Fe-Fe对的增加而发生的，这是由于Fe原子的原子尺寸效应和非线性磁耦合增加了Fe的配位数。这为溅射Fe-Y非晶态合金中的单相SG提供了一种机制。最后，我们提出了一种介于晶体结构和非晶态结构之间的理论。对Fe的应用表明，当沿bcc-非晶线的原子间距(Delta)涨落大于0.05时，bcc Fe的铁磁性变得不稳定。在Ni的情况下，我们发现居里温度随着沿面心立方-非晶线的增量的增加而迅速降低。较少

We have developed a finite-temperature theory of amorphous magnetic alloys on the basis of the functional integral method, combining the distribution function method describing random distribution of local magnetic moments with the geometrical-mean model for electronic structure calculations in amorphous alloys. applying our theory to amorphous Fe-Zr alloys whose ferromagnetism is destroyed by structural disorder, and amorphous Co-Y alloys with ferromagnetism enhanced by the structural disorder, we clarified the effects of structural disorder on their electronic structures and various magnetic properties. Next, we applied the theory to amorphous TM-Y (TM=Mn, Fe, Co, Ni) alloys showing peculiar magnetism, and showed that the most random atomic configuration explains the over-all features of their magnetic phase diagrams such as the appearance of spin glass (SG) in Mn-Y,the SG-F (ferromagnetism)-P (paramagnetism) transition in melt-spun Fe-Y,and the F-P transition in Co-Y and Ni-Y alloys … More . The theory also explained the concentration and temperature dependences of magnetizations and susceptibilities, semi-quantitatively. These magnetism is caused by the antiferromagnetic couplings between Mn local moments (Mn-Y), the local environment effects of magnetic moments and the nonlinear magnetic coupling between Fe local moments (Fe-Y), the atomic-size effects (Fe-Y and Co-Y), and 3d-4d hybridization (Co-Y and Ni-Y). We also examined the effects of atomic short range order in Fe-Y,and found that the F-SG transition occurs with increasing Fe-Fe pairs because of the increasing coordination number of Fe via atomic-size effects and the nonlinear magnetic coupling. This gives a mechanism for the single-phase SG in sputtered Fe-Y amorphous alloys. Finally, we proposed a theory which interpolates between crystal and amorphous structure. The application to Fe led to the conclusion that the ferromagnetism of bcc Fe becomes unstable when the fluctuation of interatomic distance (DELTA) becomes more than 0.05 along the bcc-amorphous line. In the case of Ni, we showed that the Curie temperature is rapidly decreased by increasing DELTA along the fcc-amorphous line. Less