Critical and “subcritical” magnetic states of an amorphous rare earth spin glass

Abstract

Small angle neutron scattering from amorphous TbFe 2 above the magnetization-determined T c = 409 K shows a conventional Lorentzian line shape with a spin correlation length which increases to only about 135 Å at T c. Below T c the scattering is no longer Lorentzian but can be represented by a sum of Lorentzian and Lorentzian squared terms as predicted theoretically for a random anisotropy field amorphous magnet. Application of an external field in the range 2−12 kG at 295 K sharply suppresses the scattering reflecting an increase in the ferromagnetic component with field. The residual magnetic scattering exhibits a prolate distortion of the intensity with respect to the direction of H, with a marked reduction in the correlation length with field indicating a spin-cluster-like response. From the magnitude of the distortion, an average number of spins per cluster as a function of field has been calculated using a super-paramagnet model.