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 tCo and the bi-layer number N by extraordinary Hall effect measurements. The perpendicular coercive field Hc decreases with the increase of tCo, excepting a very thin thickness of 1 A. While a threshold temperature (Tth) of Hc vanishing linearly increases with the increase of tCo. The Hc and Tth 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 Hc. A marked improvements for the heat assisted MRAM application was attained by air annealing of [Co(1.7 A)Pd(8 A )]30 at 220 °C, that is, the Hc was increased from 1.3 kOe to 2.9 kOe, while Tth reduced from 210 °C to 190 °C.