Synthesis of L10 FeNi thin films via High Speed Rapid Thermal Annealing

High magnetic anisotropy materials are critical for future ultrahigh density magnetic recording and permanent magnet technologies, particularly those that are rare-earth-free and precious-metal-free. Alloys of FeNi can form a metastable high anisotropy $L$1$_{\mathrm{0}}$ phase, but convenient methods of achieving the $L$1$_{\mathrm{0}}$ ordering have remained elusive. Here we report the synthesis of high-anisotropy $L$1$_{\mathrm{0}}$-Fe$_{\mathrm{50}}$Ni$_{\mathrm{50}}$ alloys via sputtering of alternating atomic layers of Fe and Ni, followed by a high speed rapid thermal annealing (RTA). Compared to as grown FeNi (4nm) films that are magnetically soft, RTA treated samples exhibit substantial increases of coercivity by 1-2 orders of magnitude. Magnetization reversal characteristics analyzed by the first-order reversal curve (FORC) technique show the emergence of a new high-anisotropy phase after RTA, and a phase fraction is extracted. Microstructure analysis by electron diffraction reveals a corresponding appearance of previously forbidden diffractions, consistent with the $L$1$_{\mathrm{0}}$ ordering. These results demonstrate a convenient approach to achieve high-anisotropy $L$1$_{\mathrm{0}}$-FeNi.