Critical behavior and magnetic ordering in amorphous TbFe2

Abstract

The zero field small angle neutron scattering from amorphous TbFe₂ 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 and just below T_C. There is only a weak indication of a cusp in the scattering in the vicinity of T_C, and below T_C the scattering continues to increase with decreasing temperature, finally saturating below about 40 K. The Lorentzian behavior observed above T_C gradually evolves into a power law dependence I∝Q⁻ⁿ with n≊3 for temperatures below about 300 K. This subcritical scattering can also be approximately represented by the sum of Lorentzian (L) and Lorentzian‐squared (L²) terms as suggested for random anisotropy field systems and yields a correlation length of 122 Å at 295 K. On application of a field in the range 2–12 kG at 295 K, the overall scattering at low Q is sharply suppressed indicating 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 which demonstrates that the remaining spin clusters do not exhibit a ferromagnetic response.