L10 FePt thin films of varying composition were epitaxially grown at different substrate temperatures (400-600° C) on MgO (100) single crystal substrate by magnetron co-sputtering technique. Processing conditions were optimized to produce films with either (002) or a mixture of (002) and (200) crystallites. Effects of two different crystallographic orientations, i.e., (200) and (002) on the magnetic properties of L10 FePt were studied. Anomalous temperature variation of coercivity (Hc) (i.e., a decrease in Hc with decreasing temperature) was observed at low temperatures for the films having comparable intensities of (200) and (002) diffraction peaks in the X-ray diffraction patterns. We have identified the cause for this anomalous behavior in Hc. Strong inter-particle exchange interaction between (200) and (002) crystallites is shown to be responsible for the anomalous temperature variation in Hc.
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