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

显示异常磁行为的非晶合金结构与磁性的理论研究

基本信息

批准号：
05640428
负责人：
KAKEHASHI Yoshiro
金额：
$ 1.15万
依托单位：
Hokkaido Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1995
项目状态：
已结题

项目摘要

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

我们在泛函积分法的基础上发展了非晶磁性合金的有限温度理论，将描述局部磁矩随机分布的分布函数方法与应用我们的理论计算非晶合金电子结构的几何平均模型相结合。针对结构无序铁磁性被破坏的非晶Fe-Zr合金和结构无序铁磁性增强的非晶Co-Y合金，阐明了结构无序对其铁磁性的影响。接下来，我们将该理论应用于表现出特殊磁性的非晶TM-Y（TM=Mn、Fe、Co、Ni）合金，并表明最随机的原子构型解释了它们的整体特征。磁相图，例如 Mn-Y 中旋转玻璃 (SG) 的出现、熔纺 Fe-Y 中的 SG-F（铁磁性）-P（顺磁性）转变、Co-Y 中的 F-P 转变以及Ni-Y 合金...更多。该理论还半定量地解释了磁化强度和磁化率的浓度和温度依赖性，这些磁性是由 Mn 局部矩 (Mn-Y) 之间的反铁磁耦合（磁矩的局部环境效应）引起的。以及 Fe 局部矩 (Fe-Y) 之间的非线性磁耦合、原子尺寸效应（Fe-Y 和 Co-Y）以及 3d-4d 杂化（Co-Y 和 Co-Y）我们还研究了 Fe-Y 中原子短程有序的影响，发现随着 Fe-Fe 对的增加，由于原子尺寸效应和 Fe 配位数的增加，F-SG 转变发生。这给出了溅射 Fe-Y 非晶合金中单相 SG 的机制。最后，我们提出了一种在晶体和非晶结构之间进行插值的理论，得出了 bcc 的铁磁性的结论。当沿 bcc 非晶线的原子间距离 (DELTA) 波动超过 0.05 时，Fe 变得不稳定。在 Ni 的情况下，我们发现随着沿 fcc 非晶线增加 DELTA，居里温度会迅速降低。