Sensitivity to temperature perturbations of the ageing states in a   re-entrant ferromagnet
  Dynamic magnetic properties and ageing phenomena of the re-entrant ferromagnet (Fe0.20Ni0.80)75P16B6Al3 are investigated by time dependent zero field cooled magnetic relaxation, m (t), measurements. The influence of a temperature cycling (perturbation), +/- *T, (prior the field application) on the relaxation rate is investigated both in the low temperature re-entrant spin glass 'phase' and in the ferromagnetic phase. In the ferromagnetic phase the influence of a positive and a negative temperature cycle (of equal magnitude) on the response is almost the same (symmetric response). The result at lower temperatures, in the RSG 'phase' is asymmetric, with a strongly affected response for positive, and hardly no influence on the response for negative temperature cycles. The behaviour at low temperatures is similar to what is observed in ordinary spin glasses. 
Kristian Jonason and Per Nordblad (Dept. of Materials Science, Uppsala   University, Uppsala, Sweden)