Abstract: ESR study of a Ni-Mn spin-glass alloy

Abstract

Electron spin resonance (ESR) measurements at fixed frequency (∼9 GHz) were made on a disordered Ni-Mn alloy of ∼26 at. % Mn which has typical spin-glass properties below Tg∼80 K. For the alloy cooled to 4 K in zero field, a broad resonance was observed whose position in field indicates the existence of an effective anisotropy field HA parallel to the magnetization M. After cooling to 4 K in +10 kOe, equally intense but sharper resonances were seen at the positive and negative fields that are unequal in magnitude, although M at these two fields is essentially equal and opposite. The unidirectional component of HA thus determined agrees closely with the field displacement of the magnetic hysteresis loop, for which the two negative coercivities are evidenced in the ESR spectrum at low fields. Upon warming, the field asymmetry of the ESR spectrum decreases rapidly and disappears at ∼25 K, where HA has become entirely uniaxial (reversing completely with M) though its magnitude is almost unchanged. At higher temperatures, HA decreases steadily and vanishes just above Tg. These results extend significantly beyond those of an earlier ESR study of Ni-Mn, for which the resonances in fields parallel but not antiparallel to the field applied during cooling were reported.1 a) Permanent address: Physics Department, University of Illinois at Chicago, Chicago, IL 60680. Work supported in part by NSF Grant No. DMR78-12777. 1 V. S. Pokatilov, I. M. Puzei, and G. A. Ivanov-Smolenskii, Sov. Phys. Solid State 21, 97 (1979).