Magnetic Properties and Structure of Icosahedral Cluster Alloys

研究了由二十面体团簇组成的三维过渡金属晶体和非晶合金的自旋涨落、磁体积效应、超磁跃迁、低温比热。主要结果如下：1)La(Fe_xAI1_<-x>)_<13>的磁相图和自旋涨落在反铁磁性和铁磁性之间的相边界附近的磁相图与Moriya-Usami提出的自旋涨落理论预测的相图非常相似。(2) La(Fe_xSi_< -x>)_<13>的巨体积磁致伸缩和居里温度的控制。在超磁跃迁后，La(Fe_xSi_<1-x>)_<13>出现了巨体积磁致伸缩效应。从实际应用的角度出发，对居里温度的控制进行了研究，证实了Co的加入是有效的。3) La(Co_<1-x>Mn_x)_<13>晶体和非晶态磁性能的比较。无定形磁矩与晶态磁矩的浓度依赖性不同。非晶合金形成二十面体团簇的浓度范围比结晶合金宽。4) La(Co_<1-x>TM_x)_<13>非晶合金的结构。研究了La(Co_<1-x>Cr_x)_<13>和La(Co_<1-x>Mn_x)_<13>非晶合金的结构差异。指出后一种合金中的二十面体团簇是变形的。这种差异可以用Mn和Cr之间的原子尺寸差异来解释。

Spin fluctuations, magnetovolume effects, metamagnetic transition, low temperature specific heat of 3d transition metal crystals and amorphous alloys composed of icosahedral clusters have been investigated. The main results are summarized as follows :1) Magnetic phase diagram and spin fluctuations of La(Fe_xAI1_<-x>)_<13>Magnetic phase diagram near the phase boundary between the antiferromagnetism and the ferromagnetism is very similar to the phase diagram predicted by the spin fluctuation theory proposed by Moriya-Usami.2) Giant volume magnetostriction and the control of the Curie temperature of La(Fe_xSi1_<-x>)_<13>After the metamagnetic transition just above the Curie temperature, a giant magnetovolume effect has been observed in La(Fe_xSi_<1-x>)_<13>. From the practical point of view, the control of the Curie temperature has been investigated and it has been confirmed that the addition of Co is effective.3) Comparison between magnetic properties of La(Co_<1-x>Mn_x)_<13> in crystalline and amorphous states.The concentration dependence of the magnetic moment in the amorphous state is different from that in the crystalline state. The concentration range where the icosahedral clusters are formed for the amorphous alloys is wider than that for the crystalline alloys.4) Structures of La(Co_<1-x>TM_x)_<13> amorphous alloys.Structural differences between La(Co_<1-x>Cr_x)_<13> and La(Co_<1-x>Mn_x)_<13> amorphous alloys have been investigated. it has been pointed out that the icosahedral clusters in the latter alloys are deformed. Such a difference is explained by the atomic size difference between Mn and Cr.