Perpendicular magnetic anisotropy and high spin-polarization ratio in epitaxial Fe-N thin films

Abstract

We have demonstrated a general framework for realizing and modulating perpendicular magnetic anisotropy in a rare-earth-element and heavy-metal-free material system. Using GaAs(001)/Fe(001) template, we have developed a synthesis scheme to produce epitaxial body center tetragonal Fe-N with (001) texture. By varying the N doping concentration, the crystal tetragonality ($c$/$a$) can be tuned in a relatively wide range. It is found that the Fe-N layer developed a strong perpendicular magnetic crystalline anisotropy (MCA) as it approaches the iron nitride interstitial solubility limit. Further annealing significantly improves the MCA due to the formation of chemically ordered Fe${}_{16}$N${}_{2}$. In addition to realizing an MCA up to 10${}^{7}$ erg/cm${}^{3}$, the spin polarization ratio ($P$ \ensuremath{\sim} 0.52), as probed directly by a point-contact Andreev reflection (PCAR) method, even shows a moderate increase in comparison with normal metal Fe ($P$ \ensuremath{\sim} 0.45). These combined properties make this material system a promising candidate for applications in spintronic devices and also potential rare-earth-element free magnets.