Thickness and growth temperature dependence of structure and magnetism in FePt thin films

We describe structural and magnetic measurements of polycrystalline, L1(0) chemically ordered Fe(55-60)Pt(45-40) films as a function of film thickness (from 3 to 13 nm) and growth temperature (270-370 degreesC). With increasing film thickness, the coercivity increases from about 1 kOe up to 11 kOe (growth at 400 degreesC), while for increasing growth temperature, the coercivity grows from 0.2 to 6 kOe for 4.3 nm thick films and 1.6 to 10 kOe for 8.5 nm thick films. There is a strong, nearly linear correlation between coercivity and the extent of L1(0) chemical order. In all the films there is a mixture of L1(0) and chemically disordered, fcc phases. The grain size in the L1(0) phase increases with both film thickness and growth temperature (increasing chemical order), while in the fcc phase the grain size remains nearly constant and is smaller than in the L1(0) phase. The films all contain twins and stacking faults. The relationship between the coercivity and the film structure is discussed and we give a possible mechanism for the lack of chemical order in the very thin films (lack of nucleation sites for the L1(0) phase). (C) 2003 American Institute of Physics.