Temperature dependent chemical ordering in FePt(001) and FePt(110) films

The growth temperature is one of the critical parameters in the formation of the chemically ordered L1₀ phase in FePt. To uniquely determine the influence of growth temperature, while other growth parameters remain fixed, we present the "temperature wedge method" where a calibrated temperature gradient of several hundred Kelvin is established across the substrate during co-deposition of Fe and Pt. Samples were deposited in a temperature range of 250°C-600°C simultaneously on MgO(001) and MgO(110) substrates. The Fe_≈50Pt_≈50 composition was verified by Rutherford backscattering. The chemical order parameter, S, at different positions along the samples, i.e., at different growth temperatures, was determined by x-ray diffraction measurements, and it was found that at all temperatures S(001) > S(110). Perpendicular and in-plane magneto-optic Kerr hysteresis loop measurements indicate large magnetic anisotropy at the "hot ends" of the samples, corresponding to large values of S.