Exchange bias at the ferro-ferrimagnet interface in PrDyCoFeB/$\alpha$-Fe microwires

The exchange bias 50–70 Oe has been observed in two-components microwires of two types: (i) with an $\alpha$-Fe shell deposited on a nanocrystalline PrDyCoFeB core and (ii) with nanocrystalline Pr-DyCoFeB shell and $\alpha$-Fe core formed spontaneously during melt solidification. In this case, the exchange bias is not observed in microcrystalline microwires consisting mainly of the (PrDy)$_{2}$(CoFe)$_{14}$B phase coated with $\alpha$-Fe. Since the nanocrystalline microwires contain, in addition to this phase, also ferromagnetic Dy(CoFe)$_{2}$ or Dy(CoFe)$_{4}$B phases, the appearance of the exchange bias is explained by the existence of the $\alpha$-Fe interface with these phases.