Realizing large out-of-plane magnetic anisotropy in L10-FeNi films grown by nitrogen-surfactant epitaxy on Cu(001)

Abstract

Rare-metal free ferromagnetic material $L{1}_{0}$ FeNi with large uniaxial magnetic anisotropy has attracted much attention for broad use of magnetic materials in various applications. While single-crystal films of $L{1}_{0}$ FeNi can be made by layer-by-layer epitaxial growth, magnitude of the uniaxial anisotropy has been lower than expected because of the imperfection of the crystal atomic structure. Here, a nitrogen (N) -surfactant epitaxial growth below 150 K is employed for overcoming interlayer mixing of the atoms at the interface. Ordered $L{1}_{0}$ FeNi films are successfully prepared on the Cu(001) substrate precovered by a ${\mathrm{Ni}}_{2}\mathrm{N}$ monolayer. The role of the N surfactant and the absence of the intermixing among Fe and Ni during the deposition and annealing processes were investigated by scanning tunneling microscopy and x-ray photoemission spectroscopy. Element-specific magnetic properties were in situ studied by soft-x-ray magnetic circular dichroism (XMCD). The observed Fe hysteresis curve and XMCD of the nitrogen-covered Ni/Fe/Ni trilayer indicate an out-of-plane magnetocrystalline anisotropy large enough for dominating the film shape anisotropy. The N-surfactant epitaxy provides a useful method for fabricating well-ordered magnetic materials without rare metals.