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 K (approximate to-4.91 x 10(5) erg/ cm(3)). By cooling the sample, the easy magnetization direction becomes perpendicular to the film plane. K-eff is positive below 288 K and increases continuously upon decreasing the temperature. At 50 K, the effective anisotropy constant reaches about 2.4 x 10(7) erg/ cm(3). 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. (C) 1998 American Institute of Physics. [S0021-8979(98)00622-7].