Thermal Stability Of Ultrathin Co/Pt Multilayers

Multilayered films composed of five repetitions of Co (0.6 nm)/Pt (0.8 nm) bilayers grown in a Pt buffer layer have shown reversible structural and magnetic behaviors from room temperature to approximately 490 K during heating processes at rates of 2 K/min. The thermal evolution of the Co/Pt interfaces was monitored by X-ray diffraction and reflectivity, as well as magnetometry measurements performed in situ. Phenomenological evaluations and Monte Carlo simulations were used to determine the temperature onsets of the thermally activated diffusion processes, interfacial degradation, and loss of perpendicular magnetic anisotropy (PMA). Above this temperature, the non-linear behavior for the thermal expansion coefficient and the perpendicular saturation magnetization indicate the loss of integrity at interfaces. Our results are consistent with the degradation of Co/Pt interfaces and consequent loss of PMA driven by defect-mediated atomic migration from 500 to 750 K. Above 500 K, the atomic migration leads to deterioration of chemical modulation of the Co/Pt interfaces and the formation of a CoXPt1-X solid solution with low saturation magnetization. Below 490 K, Co/Pt multilayer films exhibit an effective linear thermal expansion coefficient of about (6.4 +/- 0.6) x 10(-6) K-1 and a remanence to saturation magnetization ratio of 0.87.