Asymmetric hysteresis cycles as a probe of local fields in metallic spin glasses (abstract)

We have studied the magnetization in the spin-glass phase of AgMn under the repetitive application of a small (10 Oe≤h≤50 Oe) magnetic field [asymmetric hysteresis cycles (L. Néel, in Proceedings of the R. A. Welch Foundation Conference on Chemical Res. II, Atomic Structure, Houston, Texas, 1958)] after the sample has been cooled in a static field H (0≤H≤1.1 kOe). When H=0, the magnetization mn in the field off state (h=0) grows as the logarithm of the number of cycles (n), while the magnetization in the on state (h≠0) Mn decreases with cycle number. This weaker response reflects an increase of the stiffness of the spin system after each cycle. At low temperature mn grows linearly with temperature, reaches a maximum around T∼0.6 Tg and decreases as Tg is approached. The effects are larger when the system is prepared in a nonequilibrium state (rapid thermal quenching, or removal of the static field H). The irreversible growth of the magnetization mn scale linearly with Tg (i.e., exchange) for samples of 0.5 and 2.6 at. % Mn concentration. We find that mn grows as the value of H is increased, reaches a maximum around H∼Tg/15 and decreases slowly at higher fields. We suggest as a possible interpretation of this phenomenon, the existence of a cavity in the distribution of local fields acting on the low temperature excitations. Additional information on the role of anisotropic forces will also be presented.