A Study of Magnetic Excitation of Concentrated Spin-Glasses

浓自旋玻璃的宏观磁性和磁相图在许多材料中具有相当普遍的特征。然而，材料之间在微观和动力学性质上存在显著差异。为了阐明自旋动力学变化的原因，我们对几种浓缩自旋玻璃系统进行了中子散射实验。选择这些系统的目的是为了探索自旋玻璃特性与磁电子巡游特性之间的关系，这是迄今为止尚未引起足够重视的问题。Fe_<65>（Ni_<0.866>Mn_<0.134>）_<35>合金是巡游电子磁体的典型代表。而Cu_2（Mn_<0.70>Ti_<0.30>）Al合金，在Cu_2MnAl Heusler合金中，磁性Mn原子被Ti原子稀释，可视为局域磁矩材料的典型成员。对于这两个系统，磁漫散射强度增加，因为该系统是朝着自旋玻璃凝固温度冷却，即使在铁磁相。Fe_<65>（Ni_<0.866>Mn_<0.134>）_<35>中的磁关联长度比Cu_2（Mn_ Ti_）Al中的大得多<0.70><0.30>.在Fe_<65>（Ni_<0.866>Mn_<0.134>）_<35>中，在自旋玻璃相和铁磁相中都观察到了明确的自旋波激发.然而，自旋波刚度和强度的温度变化行为随动量传递的值而显著变化。而在Cu_2（<0.70>Mn_Ti_3<0.30>）Al合金中，在任何温度下都只在很小的q区观察到自旋波。

Macroscopic magnetic properties and magnetic phase diagrams of concentrated spin-glasses show rather universal characteristics among many materials. However, there are marked differences among materials in the microscopic and dynamical properties. In order to elucidate the origin of the wide variety in spin dynamics, we made neutron scattering experiments of several kinds of concentrated spin-glass systems. These systems were chosen with the aim of probing the relation between spin-glass characteristics and the itinerant character of magnetic electrons, on which much attention has not been paid so far. The Fe_<65>(Ni_<0.866>Mn_<0.134>)_<35> alloy can be classified as a typical example of itinerant electron magnets. On the other hand the Cu_2 (Mn_<0.70>Ti_<0.30>) Al alloy, in which magnetic Mn atoms are diluted with Ti atoms in a Cu_2MnAl Heusler alloy, can be regarded as a typical member of localized moment materials. For both systems, magnetic diffuse scattering intensity increases as the system is cooled toward the spin-glass freezing temperature even in the ferromagnetic phase. However, the magnetic correlation length in the Fe_<65>(Ni_<0.866>Mn_<0.134>)_<35> is considerably larger than that in the Cu_2(Mn_<0.70>Ti_<0.30>)Al. In Fe_<65>(Ni_<0.866>Mn_<0.134>)_<35>, Well defined spin-wave excitation is observed in spin-glass phase as well as in ferromagnetic phase. However, the temperature variation behavior of spin-wave stiffness and intensity change considerably with the value of momentum transfer. On the other hand, in Cu_2(Mn_<0.70>Ti_<0.30>)Al alloy, spin-wave is observed only in very small q-region at any temperature.