A neutron depolarization study of low temperature magnetic hardening in Fe–Nb–Cr–B–Cu nanocrystalline alloys

The magnetic properties of nanocrystalline Fe73,5Nb4.5Cr5B16Cu1 alloy have been studied by neutron depolarization (ND) and magnetization measurements in a temperature range between 2 and 300 K. The obtained data have confirmed the strong magnetic hardening at low temperatures characterized by rapid increase of coercive field by nearly two orders of magnitude below ~30 K. We show that this hardening goes along with the significant irreversibility between field-cooling (FC) and zero-field cooling magnetization at low fields. The three-dimensional neutron depolarization analysis allowed us to characterize simultaneously the macroscopic magnetization, the magnetic domain size and texture. It is shown that a significant role in the magnetic behavior at low temperatures is played by the presence of spin freezing effects.