# Magnetism and structure of in-situ grown FeN films studied using N K-edge XAS and nuclear resonance scattering

## TL;DR

This study investigates the structural and magnetic evolution of in-situ grown FeN thin films, revealing a transition from magnetic rock-slat to non-magnetic zinc-blende structures as film thickness increases, using advanced synchrotron techniques.

## Contribution

It provides new insights into the growth-dependent structural and magnetic properties of FeN films, resolving longstanding debates about their phases and magnetic states.

## Key findings

- Ultrathin FeN films show a magnetic structure with RS-type configuration.
- A transition from RS-type to ZB-type structure occurs beyond 5 nm thickness.
- The structural change correlates with the emergence of magnetic properties in ultrathin films.

## Abstract

We studied the structural and magnetic properties of \textit{in-situ} grown iron mononitride (FeN) thin films. Initial stages of film growth were trapped utilizing synchrotron based soft x-ray absorption near edge spectroscopy (XANES) at the N $K$-edge and nuclear resonant scattering (NRS). Films were grown using dc-magnetron sputtering, separately at the experimental stations of SXAS beamline (BL01, Indus 2) and NRS beamline (P01, Petra III). It was found that the initial stages of film growth differs from the bulk of it. Ultrathin FeN films, exhibited larger energy separation between the t$_{2g}$ and e$_g$ features and an intense e$_g$ feature in the N $K$-edge pattern. This indicates that a structural transition is taking place from the rock-slat (RS)-type FeN to zinc-blende(ZB)-type FeN when the thickness of films increases beyond 5\,nm. The behavior of such N $K$-edge features correlates very well with the emergence of a magnetic component appearing in the NRS pattern at 100\,K in ultrathin FeN films. Combining the \textit{in-situ} XANES and NRS measurements, it appears that initial FeN layers grow in RS-type structure having a magnetic ground state. Subsequently, the structure changes to ZB-type which is known to be non-magnetic. Observed results help in resolving the long standing debate about the structure and the magnetic ground state of FeN.