Direct Observation of Giant Saturation Magnetization in Fe16N2

TL;DR

This paper reports the direct measurement of an exceptionally high saturation magnetization in Fe16N2 thin films, confirming long-standing predictions and advancing understanding of magnetic properties in this compound.

Contribution

It provides the first direct observation of giant saturation magnetization in Fe16N2 using polarized neutron reflectometry, validating a theoretical model and overcoming previous measurement challenges.

Findings

Giant saturation magnetization up to 2500 emu/cm³ observed

Polarization-dependent XANES confirms charge transfer features

Results support the Cluster + Atom model for Fe16N2

Abstract

Magnetic materials with giant saturation magnetization have been a holy grail for magnetic researchers and condensed matter physicists for decades because of its great scientific and technological impacts. As described by the famous Slater-Pauling curve the material with highest Ms is the Fe65Co35 alloy. This was challenged in 1972 by a report on the compound Fe16N2 with Ms much higher than that of Fe65Co35. Following this claim, there have been enormous efforts to reproduce this result and to understand the magnetism of this compound. However, the reported Ms by different groups cover a broad range, mainly due to the unavailability of directly assessing Ms in Fe16N2. In this article, we report a direct observation of the giant saturation magnetization up to 2500 emu/cm3 using polarized neutron reflectometry (PNR) in epitaxial constrained Fe16N2 thin films prepared using a low-energy and surface-plasma-free sputtering process. The observed giant Ms is corroborated by a previously proposed Cluster + Atom model, the characteristic feature of which, namely, the directional charge transfer is evidenced by polarization-dependent x-ray absorption near edge spectroscopy (XANES).