Pt layer thickness dependence of magnetic properties in Co/Pt multilayers

Abstract

The magnetic properties of Co/Pt multilayer films prepared by dc sputtering have been investigated using ferromagnetic resonance and a vibrating sample magnetometer. The thickness of the Co layer is constant at 25 Å while the thickness of the Pt layer varies from 0.9 to 18 Å. The saturation magnetization per unit volume of Co is nearly constant for all the films and close to that of bulk Co. In the ferromagnetic resonance spectra, the presence of two resonance modes having an amplitude ratio that varies substantially with the Pt thickness is strong evidence that a significant coupling between cobalt layers exists even at 18 Å of Pt. For Pt thicknesses greater than 3.6 Å, a uniaxial perpendicular magnetic anisotropy field component increases with Pt thickness and saturates at about 9.0 Å. If the induced anisotropy energy is attributed to a surface anisotropy energy at the Co/Pt interface, it has a value Ks of approximately 0.57 erg/cm2. The temperature dependence of the magnetic hysteresis loop and the ferromagnetic resonance spectrum indicate an increase in the uniaxial anisotropy field with decreasing temperature.