Hf2Co11 thin films: Rare-earth-free permanent nanomagnets

Abstract

Hf2Co11 thin films were deposited on single crystalline Si(100) substrates by using conventional direct current (DC) magnetron sputtering with a Hf2Co11 alloy target. All films were grown at room temperature with 120W sputtering power. In order to obtain the composition of the desired, the working pressure was changed from 0.66 to 1.05Pa. The relationships between structural and magnetic properties in Hf-Co films were studied by using differential thermal analyzer, glancing incidence X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, atomic force microscopy, magnetic force microscopy and vibrating sample magnetometer. It revealed that the as-deposited films were amorphous at room temperature for all deposition pressures and showed soft ferromagnetic phase. In order to increase the coercive field associated with an advancing transition to hard phase, thin films were post-annealed from 773K to 973K. Post-annealing process led to a high remanence magnetization and improved the squareness of the demagnetization curve. Their saturation magnetization values varied from 515 to 1378kA/m and also coercive field values varied from 52x10−4 to 153x10−3 T at room temperature depending on post-annealing temperatures. Hf2Co11 soft ferromagnetic phase was modified by formation of post-annealing and was given rise to enhance permanent magnet properties (saturation magnetization, coercive field, energy product). The magnetic properties of thin films were found to be convenient for nanomagnet applications.