Spin-reorientation transition in $\alpha$-Fe microwires with an amorphous PrDyCoFeB shell

A spin-reorientation transition accompanied by a decrease in the longitudinal magnetization of $\alpha$-Fe/PrDyCoFeB microwires was observed at 245 K in zero magnetic field. An increase of the magnetic field at which the microwire is heated from 2 K leads to a significant shift of the transition temperature from 245K at 0 T to 70 K at 1 T. In the perpendicular direction, the change in magnetization at the critical transition temperature is almost absent. Jumps of the magnetic anisotropy and magnetic susceptibility are observed in low fields at a critical temperature. The magnetic phase transition is due to a transition between the ferrimagnetic state of the PrDyCoFeB shell at high temperatures and the state of Ising spin glass at low temperatures.