Aging and rejuvenation in a ferromagnetic Ni 3 Al

Aging and rejuvenation phenomena, recently observed in ferromagnetic-like phases of complicated magnets, are studied using a simple itinerant-electron ferromagnet, Ni 3 Al. Results show that relaxation times of the magnetic response are widely distributed, hence, magnetic domain walls are collectively pinned in a multi-valley structured potential. The absorptive component of the ac-susceptibility gradually decreases with isothermal aging, and hence the domain-wall conformation becomes stabilized in following deeper valleys. If the temperature is shifted slightly after such isothermal aging, the absorptive component temporarily rises as if rejuvenated. This rejuvenation-like phenomenon is always accompanied by acceleration of the magnetic relaxations, regardless of cooling/heating. This thermal perturbation induced de-pinning indicates that the multi-valley structure itself significantly changes with temperature. In other words, the rejuvenation as well as aging can be explained using temperature-sensitive collective pinning of magnetic domain walls. We can hence say that they are intrinsic properties in actual ferromagnets with irregularly distributed pinning centers. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2015