Hydrogen absorption-induced reversible change in magnetic properties of Co-Pd alloy films

The effects of reversible hydrogen absorption on the magnetism of Co-Pd alloy thin films were investigated. Evident enhancement of magnetic coercivity H_c 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 H_c for 20 nm Co₃₉ Pd₆₁, whereas the H_c 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 H_c and squareness as well as the reduction of Kerr rotation angle.