A Study of Magnetic Excitation of Concentrated Spin-Glasses

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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.