Alnico thin films with high coercivities up to 6.9 kOe

Abstract

The spinodal decomposition has been investigated in Alnico thin films prepared by sputtering. The as-made bcc thin films were heat treated both by the complex heat treatment of bulk Alnico magnets and by a simple annealing at different temperatures in the range of 600-900 °C. The simple heat treatment gave a coercivity of 2.6 kOe at 600°C and 6.9 kOe at 800°C. The maximum coercivity observed is approximately ten times larger than the bulk Alnico V value. Electron diffraction patterns can be mostly indexed to a new fcc phase with a=7.79 Å. The traditional Alnico heat treatment gave a similar coercivity (6.7 kOe after full heat treatment) and similar diffraction patterns. The coercivity was found to depend strongly on the film thickness. In samples with thickness above 100 nm, the coercivity declined dramatically and at 150 nm it was only 500 Oe. These findings suggest structural transformations in films which are drastically different from the spinodal decomposition observed in bulk Alnico.