Synthesis, characterization and modeling of high quality ferromagnetic Cr-doped AlN thin films

TL;DR

This study combines theoretical predictions and experimental methods to synthesize and analyze Cr-doped AlN thin films, revealing room temperature ferromagnetism and high Curie temperatures in the material.

Contribution

It provides new insights into the magnetic properties of Cr-doped AlN, including defect levels, impurity band formation, and ferromagnetic behavior at room temperature.

Findings

Room temperature ferromagnetism observed with Hc of 120 Oe

Over 33% of Cr is magnetically active at room temperature

Predicted Curie temperatures exceed 600 K for certain compositions

Abstract

We report a theoretical and experimental investigation of Cr-doped AlN. Density functional calculations predict that the isolated Cr t2 defect level in AlN is 1/3 full, falls approximately at midgap, and broadens into an impurity band for concentrations over 5%. Substitutional Al1-xCrxN random alloys with 0.05 <= x <= 0.15 are predicted to have Curie temperatures over 600 K. Experimentally, we have characterized and optimized the molecular beam epitaxy thin film growth process, and observed room temperature ferromagnetism with a coercive field, Hc, of 120 Oersted. The measured magnetic susceptibility indicates that over 33% of the Cr is magnetically active at room temperature and 40% at low temperature.