Critical behavior and magnetic ordering in amorphous TbFe2

Abstract

The zero field small angle neutron scattering from amorphous TbFe2 above the magnetization-determined TC =409 K shows a conventional Lorentzian line shape with a spin correlation length which increases to only about 135 Å at and just below TC. There is only a weak indication of a cusp in the scattering in the vicinity of TC, and below TC the scattering continues to increase with decreasing temperature, finally saturating below about 40 K. The Lorentzian behavior observed above TC 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.