Remanence in spin glasses : A new approach from zero field NMR in CuMn

Abstract

Zero field Cu NMR of the first and fourth nearest neighbours of Mn in spin glass CuMn (concentrations from 0.4% to 4.7%) have been detected for TA induced (as σ) by the cooling field H_c, the anisotropy energy being roughly a constant. Transverse susceptibility and NMR intensity analyses confirm that most Mn spins are involved in the collective response to a transverse field and that H_A is defined on a macroscopic scale. Direct observation by NMR of the shifted hysteresis loops and comparison with magnetization data imply that H_A includes both an uniaxial H_ax) and an unidirectional (H_d) anisotropy field, and that the magnetization reversals, when detected, occur for fields ‖H_o+H_d‖ax. The simultaneous occurrence of collective and irreversible phenomena in spin glasses is discussed.