Giant exchange anisotropy observed in Mn-Ir/Co-Fe bilayers containing ordered Mn₃Ir phase

Exchange anisotropy of Mn₇₃Ir₂₇/Co ₇₀Fe₃₀ bilayers fabricated on a 50-nm-thick Cu under layer by changing the substrate temperature (T_sub) during the deposition of Mn-Ir layer was investigated, correlating with the crystallographic structure of Mn-Ir layer. The unidirectional anisotropy constant (J_K) of the bilayers remarkably varied as a function of T_sub. After the thermal annealing of bilayers at 320°C in a magnetic field of 1 kOe, J_K steeply increased from 0.3 to 1.3 erg/cm², as T_sub was raised from room temperature to 170°C. The blocking temperature was enhanced from 270 to 360 °C, simultaneously. The J_K of 1.3 erg/cm ² is nearly ten times larger than the values reported in Mn-Ir/Co-Fe bilayers early in the research of them. The x-ray diffraction profiles showed that the ordered Mn₃Ir phase was formed in the antiferromagnetic layer with increasing T_sub. From the coincidence of enhancing J _K and increasing peak intensity of superlattice diffraction lines, the Mn₃Ir phase was suggested to be an origin of the giant J _K and the high blocking temperature.