Thickness and Growth Temperature Dependence of Structure and Magnetism in FePt Thin Films Michael F. Toney[a], Wen-Yaung Lee[b], Jonathan A. Hedstrom and Andrew Kellock

We describe structural and magnetic measurements of polycrystalline, L10 chemical-ordered Fe(55-60)Pt(45-40) lms as a function of lm thickness (from 3 to 13 nm) and growth temperature (270 370 C). With increasing lm thickness, the coercivity increases from about 1 kOe up to 11 kOe (growth at 400C), while for increasing growth temperature, the coercivity grows from 0.2 to 6 kOe for 4.3 nm thick lms and 1.6 to 10 kOe for 8.5 nm thick lms. There is a strong, nearly linear correlation between coercivity and the extent of L10 chemical order. In all the lms there is a mixture of L10 and chemically disordered, fcc phases. The grain size in the L10 phase increases with both lm thickness and growth temperature (increasing chemical order), while in the fcc phase the grain size remains nearly constant and is smaller than in the L10 phase. The lms all contain twins and stacking faults. The relationship between the coercivity and the lm structure is discussed and we give a possible mechanism for the lack of chemical order in the very thin lms (lack of nucleation sites for the L10 phase). PACS numbers: 75.50.SS, 75.50.Vv, 68.55.Jk, 61.10.Nz Electronic address: [email protected]