Magnetic properties and microstructure of vapour-deposited Fe/Hf films upon thermal annealing

Fe/Hf multilayers were prepared by alternate deposition of pure hafnium and iron. As-deposited samples were then annealed at 380 degrees C and 550 deg rees C, respectively, to investigate the microstructure and magnetic proper ty changes of the films. It was found that all as-deposited Fe/Hf films exh ibited the soft ferromagnetic property where the coercive force was lower t han 30 Oe. The coercive force and the magnetic moment per Fe atom changed s ignificantly with the annealing temperature and the Fe layer thickness (t(F e)). For t(Fe), = 2.2-4.2 nm films, their soft ferromagnetic properties wer e stable upon thermal annealing at 380 and 550 degrees C, while for t(Fe) g reater than or equal to 9.5 nm and t(Hf) = 13.2 nm films, after annealing a t 550 degrees C for 20 min, as-deposited films transformed from having a so ft ferromagnetic property to having a hard ferromagnetic one. The residual magnetization and maximum magnetic energy product of the films could come u p to about 0.81 mu(B) and 8.8 kT m(-3) (1.1 MGOe), for the Fe(9.5 nm)/Hf(13 .2 nm) films annealed at 550 degrees C. It was also found that there were t wo metastable phases with fee structure in the annealed Fe-Hf films. The ma gnetic change mechanism was discussed in terms of interdiffusion in the Fe/ Hf interface and phase transformation in the films upon thermal annealing.