Structural control of magnetic properties in Co/Pd multilayer for heat assisted perpendicular MRAM application

Temperature dependence of magnetic properties in [Co/Pd]_N multilayer have been systematically studied for lithographically patterned samples with different Co thicknesses t_Co and the bi-layer number N by extraordinary Hall effect measurements. The perpendicular coercive field H_c decreases with the increase of t_Co, excepting a very thin thickness of 1 Å. While a threshold temperature (T_th) of H_c vanishing linearly increases with the increase of t_Co. The H_c and T_th monotonously increases with the increase of N, ranged from 5 to 50. The superior crystalline structure for samples with the larger N was confirmed from enhanced Co/Pd(111) peak height in the XRD pattern. A practical thermal activation coefficient α of 174 was evaluated from a sweep rate dependence of H_c. A marked improvements for the heat assisted MRAM application was attained by air annealing of [Co(1.7 Å)Pd(8 Å)]₃₀ at 220°t, that is, the H_c was increased from 1.3 kOe to 2.9 kOe, while T_th reduced from 210°C to 190°C.