Phase, microstructure and intrinsic magnetic properties evolutions of AlNiCo5 films

AlNiCo permanent magnets are well-known for their remarkable thermal stability and ultra-high Curie temperatures, which are suitable for applications in high temperature micro-electromechanical systems. In this work, we systematically investigate the effects of varying annealing temperatures and sputtering parameters on the properties, phase, and microstructure of AlNiCo 5 film. We demonstrate spinodal decomposition (SD) transformation occurs in AlNiCo films after annealing. However, the microstructures of these films are markedly different from traditional SD nanostructures in bulk AlNiCo. As the annealing temperature increases, the SD transformation progress becomes more completely. Furthermore, when sputtering power is low (35 W), the coercivity of the film could reach 597.31 Oe, close to that of bulk AlNiCo, but the M_s was only 6.4 kGs. In contrast, at higher sputtering power (80 W), M_s increased to 12.5 kGs but displayed a lower coercivity of 286 Oe. The coercivity mechanism of AlNiCo films is primarily attributed to the pinning effect induced by non-magnetic amorphous phases. Additionally, the thermal stability of most AlNiCo films only slightly reduces compared to bulk AlNiCo, but remain obviously higher than rare-earth permanent magnets. This study provides valuable insights into understanding the intrinsic magnetic properties and thermal stability of AlNiCo thin films.