The magnetic and microstructural properties of Pt/Co multilayers grown on ZnO

We measured the magnetic properties and examined the microstructure of Pt/Co multilayers sputtered at ambient temperature on ZnO underlayers grown between 25 and 500 °C. For ZnO grown at 150 °C, the perpendicular magnetic anisotropy energy of Pt/Co multilayers was a maximum, ∼1.1×107 erg/cm3, and then decreased monotonically to ∼3×106 erg/cm3 for ZnO grown at 500 °C. From measuring the angular dependence of magnetic coercivity, we deduced that magnetic reversal was by domain-wall motion in multilayers on low temperature (≤200 °C) ZnO, and predominantly by rotation on high-temperature ZnO. By cross-sectional transmission electron microscopy of Pt and Co layers on ZnO, we determined that all layers were rougher for high ZnO growth temperatures, although higher temperature promoted better multilayer (111)-fcc texture. The microstructure of Pt/Co multilayers on high-temperature ZnO was also particulate or granular, compared to more continuous on low-temperature ZnO. We concluded that the multilayer roughness reduced perpendicular magnetic anisotropy, and that particulate structural features caused magnetic reversal by rotation.