Temperature induced perpendicular magnetic anisotropy in Co/Cu/Co trilayers

The evolution of the magnetic anisotropy between room temperature and 50 K has been studied using torque magnetometry on a hcp (0001) Co (0.8 nm)/Cu (1.5 nm)/Co (0.8 nm) trilayer prepared by ultrahigh vacuum evaporation. At 300 K this sample presents an easy plane of the magnetization in the film plane, with a very small effective anisotropy constant Keff (≈−4.91×105 erg/cm3). By cooling the sample, the easy magnetization direction becomes perpendicular to the film plane. Keff is positive below 288 K and increases continuously upon decreasing the temperature. At 50 K, the effective anisotropy constant reaches about 2.4×107 erg/cm3. This strong increase of the effective anisotropy upon decreasing the temperature can be explained by a strong increase of surface anisotropy term. Magnetization measurements have revealed the existence of one magnetically dead monolayer at each interface, indicating a strong intermixing in our Co/Cu interfaces at 300 K. Thus the evolution of the magnetism of the intermixed region as a function of the temperature may be at the origin of the strong increase of the effective anisotropy.