Effect of underlayer on formation of L12 phase and resultant giant exchange anisotropy in Mn-Ir/Co-Fe bilayers

The effect of a 5 nm thick Cu underlayer on the formation of Mn₃Ir (L1₂) phase is investigated in Mn-Ir/Co-Fe bilayers. The multilayers are deposited on thermally oxidized Si wafers by magnetron sputtering. The microstructure and magnetic properties of the films are examined at room temperature by X-ray diffraction and grazing incident X-ray diffraction, and with a vibrating sample magnetometer, respectively. The unidirectional anisotropy constant, J_K, is then calculated with the equation of J_K = M_s·d_F·H_ex, where M_s·d_F is the areal saturation magnetization of Co-Fe layer, and H_ex is the exchange biasing field determined as a shift of the center of MH-loop along the field axis. An enhancement on J_K is observed with a maximum value of 1.15 erg/cm² at T_sub = 130°C and T_a = 320°C.