The effects of reversible hydrogen absorption on the magnetism of Co-Pd alloy thin films were investigated. Evident enhancement of magnetic coercivity Hc and squareness, measured by magneto optical Kerr effect (MOKE), was observed in the magnetic hysteresis loops of films with Pd content of 61%, 76%, and 86%, whereas no observable changes were noted in the MOKE hysteresis loops of Co-rich alloy films. For Co39 Pd61, perpendicular magnetic anisotropy increased as film thickness increased from 10 to 20 nm. Hydrogenation induced three times enhancement of perpendicular Hc for 20 nm Co39 Pd61, whereas the Hc change in 10 nm Co39 Pd61 was within 10%. A Pd-rich alloy composition and appropriate film thickness for perpendicular magnetization are both crucial for hydrogen absorption-induced effect on magnetic properties, i.e. the enhancement of Hc and squareness as well as the reduction of Kerr rotation angle.
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