The effect of sol–gel preparation conditions on structural characteristics and magnetic properties of M-type barium hexaferrite thin films

Abstract

© 2015, Springer Science+Business Media New York. Abstract: We have shown the possibility to obtain M-type barium hexaferrite thin films with thickness of ~200–450 nm on the surface of dielectric α-Al<inf>2</inf>O<inf>3</inf> substrates with low microwave dielectric loss (tan δ ~ 10⁻⁴ GHz) by a sol–gel method. For the production of high-dense homogeneous thin films of M-type barium hexaferrite (BaFe<inf>12</inf>O<inf>19</inf>, BHF) with nanorod-like grains and a uniform distribution of iron and barium ions, we have studied the synthesis conditions for thermally stable film-forming solutions with high concentrations of barium ions. Films with a c-axis magnetic texture were obtained by spin-coating the former solutions on α-Al<inf>2</inf>O<inf>3</inf> substrates and annealing at temperatures between 473 and 1073 K. The resulting textured M-type BHF films have demonstrated the following magnetic parameters: H<inf>c⊥</inf> = 334 kA/m, H<inf>c||</inf> = 167 kA/m; M<inf>s⊥</inf> = 0.005 emu, M<inf>s||</inf> = 0.003 emu for the films’ thickness of ~200 nm, and H<inf>c⊥</inf> = 360 kA/m, H<inf>c||</inf> = 338 kA/m; M<inf>s⊥</inf> = 0.009 emu, M<inf>s||</inf> = 0.007 emu for the films’ thickness of ~450 nm. These M-type BHF thin films can serve as a promising basis for further development of multilayer microwave resonant elements. Graphical Abstract: [Figure not available: see fulltext.]