Large magnetostriction in '-Fe₄N single-crystal thin film

An Fe4N(110) single-crystal film of 50 nm thickness with gamma' phase is prepared through hetero-epitaxial growth on an MgO(110) single-crystal substrate at 400 degrees C by reactive sputtering. The out-of-plane and in-plane lattice constants agree with those of bulk within small differences less than 0.2% and the orientation dispersions are about 1.2 degrees. The degree of N site ordering in Fe4N structure is estimated to be 0.995. The arithmetical mean surface roughness is as small as 0.3 nm. These data show that a high-quality Fe4N single-crystal film is successfully formed. The Fe4N film shows in-plane magnetic anisotropy with the easy magnetization direction parallel to [0 0 1] and with the hard direction parallel to [1_11], which is reflecting the positive magnetocrystalline anisotropy, K-1. A large negative.100 value of -40 x 10(-6) and a fairly-large positive lambda 111 value of +150 x 10(-6) are observed. The present study has shown that lambda'-Fe4N compound is one of the strong candidates for rare-metal-free magnetostrictive materials.