Magnetic and magnetocaloric properties of Er-Co-Al thin-film alloys

Er-Co-Al thin films with the compositions of ErCo_1.52Al_0.36, ErCo_1.69Al_0.76, and ErCo_1.87Al_0.16 were fabricated by magnetron-sputtering, and their magnetic and magnetocaloric properties were characterized in the asdeposited state and post-annealed state at 1073 K. The X-ray diffraction results indicate that the microstructure in the as-deposited state consists of an amorphous phase, which then transforms into a cubic Laves phase with C15 symmetry on annealing. The phase transformation, however, is incomplete, evidenced by the existence of Co precipitates and some oxides of Er and Al in the annealed samples. A compensation-like behavior is observed in the as-deposited samples, probably due to the sperimagnetic structure, but it disappears after annealing. The magnetic entropy change is largest for the annealed ErCo_1.87Al_0.16 sample, in which the composition is closest to the pseudo-binary Er(Co,Al)₂ compound. The observed value, however, is rather small (3.2 J/kg K in a field sweep of 0–50 kOe), due the incomplete phase transformation from the amorphous to the cubic Laves phase during annealing.