Improved thermal stability of exchange bias of Mn-Ir/Co-Fe bilayers by novel in situ thermal annealing procedure

The effect of in situ thermal annealing of Mn-Ir films under ultra-high vacuum on the metallurgical microstructure and on the thermal stability of the unidirectional anisotropy constant, JK, was investigated for Mn73Ir27/Co70Fe30 bilayers. As a result, we found that the average lateral grain size of Mn-Ir increases with increasing the in situ annealing temperature, TIR and that the shape of JK-T curve changes to convex with increasing the TIR, implying a narrowing distribution of local blocking temperature. We conclude that ultra-high vacuum annealing is effective in improving the thermal stability of the exchange anisotropy of Mn-Ir/Co-Fe bilayers through the change of lateral grain size distribution of the Mn-Ir layer.