Nonequilibrium strain and Curie temperature in as-deposited Mn ferrite thin films by RF sputtering

Nonequilibrium lattice distances and Curie temperatures have been observed in as-deposited Mn ferrite thin films by rf sputtering at RT and 300°C, although they show crystalline X-ray diffraction patterns. The (400) lattice distance is larger, while the (111), (222), and (444) lattice distances are smaller than the bulk values. This implies that a compressive stress along the [100] axis and a tensile stress along the [111] axis are present in as-deposited films. The Curie temperatures of as-deposited films are 60~160°C higher than the bulk value. The degree of the nonequilibrium is larger for the films deposited at a lower substrate temperature. The nonequilibrium in as-deposited films relaxes with heat treatment in an N2 atmosphere at 610°C