Magnetic properties of magnetron sputtered MnAl/CoNi thin films

In this work, the magnetic properties of MnAl/CoNi bilayers thin films are investigated by varying the thickness of CoNi layer and annealing temperature of the MnAl stack. The Ta(3 nm)/Mn 50 Al 50 (15 nm)/CoNi (0, 4, 6 nm)/Ta(5 nm) thin films were deposited on Si substrate using a magnetron sputtering system. Before depositing CoNi, the MnAl (15 nm) stack was annealed under two different conditions; i.e., at (i) 400 0 C for 60 min, (ii) 800 0 C for 120 min. The surface roughness of the deposited thin films was measured using a 3D optical profilometer, and the results show that the films have a smooth surface. The crystal structure and magnetic properties were investigated by X-ray diffractometer (XRD) and vibrating sample magnetometer (VSM). The XRD analyses revealed dominate ↋-phase along with τ phase of MnAl. The room temperature magnetic measurement showed that the thin film of MnAl annealed at 400 0 C exhibits diamagnetic behavior whereas thin films of MnAl(400 0 C)/CoNi (4 and 6 nm) films exhibit ferromagnetism. The saturation magnetization (M s ) decreases from 375 to 293 emu/cc when the thickness of CoNi layer was varied from 4 to 6 nm. However, the MnAl(800 0 C)/CoNi films has resulted a ferromagnetic behavior only for 6 nm thickness of CoNi. The maximum energy product of these films was in the range of 0.02–0.06 MGOe only. The observed magnetic properties are discussed in a correlation with the surface roughness and structural changes of the MnAl alloy.