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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

本文在泛函积分方法的基础上，将描述局部磁矩随机分布的分布函数方法与非晶合金电子结构计算的几何平均模型相结合，发展了非晶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合金和铁磁性被结构无序增强的非晶态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。然后，我们将该理论应用于具有特殊磁性的非晶态TM-Y（TM=Mn，Fe，Co，Ni）合金，并证明了最无规的原子组态解释了其磁相图的全部特征，如Mn-Y中自旋玻璃（SG）的出现，快淬Fe-Y中SG-F（铁磁性）-P（顺磁性）转变，Co-Y和Ni-Y合金中F-P转变 ...更多信息 .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）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Ni-Y）引起的。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，F-SG跃迁发生，这是由于Fe通过原子尺寸效应和非线性磁耦合增加了配位数。这给出了溅射Fe-Y非晶合金中单相SG的机制。最后，我们提出了一个介于晶体和非晶结构之间的理论。对Fe的应用表明，当沿体心立方非晶线原子间距（Δ）的涨落大于沿着0.05时，体心立方Fe的铁磁性变得不稳定。在Ni的情况下，我们表明，居里温度迅速降低沿面心立方非晶线增加Δ沿着。少