Applied field response of the spin glass state in amorphous NdFe2

Abstract

The magnetic correlations and the response of the spin system to an applied field have been studied in sputtered amorphous NdFe₂ using high‐resolution small angle neutron scattering (SANS) techniques. In zero field the line shape of the scattering is Lorentzian down to a spin freezing temperature of approximately 330 K. Below this temperature the line shape becomes increasingly non‐Lorentzian and has been analyzed using a Lorentzian plus Lorentzian‐squared cross section appropriate for a random anisotropy field system. The correlation length shows a broad maximum of 170 Å near 285 K (below T_c) and then decreases to a constant value of ≊80 Å for T< 100 K. SANS data taken in applied fields up to 18 kOe at 83 K produced constant intensity contours which are elliptically distorted with the Q∥H direction being the major axis. The overall intensity and the calculated spin correlation length both drop abruptly with increased field. This behavior is consistent with the field driving the dominant part of the spin system into an infinite cluster with the residual smaller spin clusters exhibiting a super‐paramagnetic type response.