Perpendicular magnetic anisotropy enhancement and thermal stability study in Co/Pt multilayers with MgO/Pt interface

Abstract

ABSTRACTThe Co/Pt multilayers with Pt and MgO/Pt underlayer were prepared by magnetron sputtering and the perpendicular magnetic anisotropy(PMA) of the multilayers were researched by the means of Anomalous Hall effect (AHE). The annealing effect study of Pt(1.0)/[Co(0.4)/Pt(0.8)]3(unit: nm) shows that the sample has pretty good thermal stability but the coercivity(HC) has little change. The experimental results show that the PMA and Hc of Co/Pt multilayers was improved greatly by the additional scattering of electrons induce from the amorphous insulator-metal interface of MgO-Pt. When MgO layer thickness(tMgO) is 4nm, the Hall resistance (RHall) of MgO(4)/Pt(1.0)/[Co(0.4)/Pt(0.8)]3 multilayer has a maximum value of 2.11Ω which is increased by 16%. Furthermore the Hc increases to 172Oe which is more than 1.5 times to Pt(1.0)/[Co(0.4)/Pt(0.8)]3 multilaye and the Hc meets the maximum value of 204Oe when tMgO is 2 nm. Annealing effects of MgO(4)/Pt(2)/Co(0.2)/Ni(0.4)/Co(0.2)/Pt(2) show that it has good thermal stability and the Hc reaches its maximum value of 438Oe at annealing temperature(TA) of 300°C. The multilayer begins to lose the PMA property at higher TA. The Hysteresis loop of MgO(4)/Pt(1.0)/[Co(0.4)/Pt(0.8)]3 multilayer annealed at 300°C was tested and the anisotropy constant(Keff) was obtained as 8.9 × 106 erg/cm3, which is about 4.45 times the Pt(1.0)/ [Co(0.4)/Pt(0.8)]3 multilayer. The PMA of Co/Pt multilayers is greatly enhanced by MgO/Pt interface and annealing treatment.