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

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Abstract
Pure Co and Pd–Co alloyfilms were prepared using electron beam evaporation and sputtering. They were characterized by superconducting quantum interference 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 temperature for the alloy of 370 K, and a preference for the moments to orient perpendicular to the film.MFM images of magnetic domains were obtained for 298 and 323 K. In the Pd–Co film, the phase contrast between the oppositely magnetized domains decreases by 35% as the temperature of the film is raised, even though the dominant length scale of the domains (about 0.25 μm) 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 the 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 properties as a function of temperature. We also observe that, while less temperature dependent, the contrast of the magnetic domain images of the Co film is smaller than that of the Pd–Co, a result most likely due to the reorientation of the moments on going from the pure Co film to the Pd–Co film.