Temperature-dependent magnetism in transition metal films observed by magnetic force microscopy and classical magnetometry

Pure Co and Pd-Co alloy films were prepared using electron beam evaporation and sputtering. They were characterized by superconducting quantum interfe rence device magnetometry and magnetic force microscopy (MFM). The magnetic hysteresis curves for the Co film show that the magnetization direction is in the plane of the film. The magnetization data reveal a Curie temperatur e for the alloy of 370 K, and a preference for the moments to orient perpen dicular to the film. MFM images of magnetic domains were obtained for 298 a nd 323 K. In the Pd-Co film, the phase contrast between the oppositely magn etized domains decreases by 35% as the temperature of the film is raised, e ven though the dominant length scale of the domains (about 0.25 mm) remains unchanged. A very different result was obtained for the pure Co film: Over the same temperature range the phase contrast in the magnetic images in th e Co film decreased only by 10%. This indicates that the observed behavior in the Pd-Co film is mainly due to the much more rapid change in magnetic p roperties as a function of temperature. We also observe that, while less te mperature dependent, the contrast of the magnetic domain images of the Co f ilm is smaller than that of the Pd-Co, a result most likely due to the reor ientation of the moments on going from the pure Co film to the Pd-Co film. (C) 1999 American Institute of Physics. [S0021-8979(99)78708-6].