Giant saturation magnetization effect in epitaxial Fe16N2 thin films grown on MgO (001) substrate

TL;DR

This study demonstrates that epitaxial strain in Fe16N2 thin films can significantly enhance their saturation magnetization, reaching up to 3.1T, by tuning the lattice constant near a spin crossover point.

Contribution

It reveals that strain engineering in epitaxial Fe16N2 films can induce a giant saturation magnetization, challenging previous beliefs based on the Slater-Pauling curve.

Findings

Ms varies from ~2.1T to ~3.1T with strain

Epitaxial strain influences the spin state of Fe in Fe16N2

Lattice tuning near a spin crossover point enhances magnetization

Abstract

Whether {\alpha}double prime-Fe16N2 possesses a giant saturation magnetization (Ms) has been a daunting problem among magnetic researchers for almost 40 years, mainly due to the unshakable faith of famous Slater-Pauling (SP) curve and poor consistency on evaluating its Ms. Here we demonstrate that, using epitaxy and mis-fit strain imposed by an underlying substrate, the in-plane lattice constant of Fe16N2 thin films can be fine tuned to create favorable conditions for exceptionally large saturation magnetization. Combined study using polarized neutron reflectometry and X-ray diffraction shows that with increasing strain at the interface the Ms of these film can be changed over a broad range, from ~2.1T (non-high Ms) up to ~3.1T (high Ms). We suggest that the equilibrium in-plane lattice constant of Fe16N2 sits in the vicinity of the spin crossover point, in which a transition between low spin to high spin configuration of Fe sites can be realized with sensitive adjustment of crystal structure.