The role of Cr substitution on the ferromagnetic properties of Ga1-xCrxN

TL;DR

This study investigates how chromium substitution affects the ferromagnetic properties of Ga1-xCrxN films, revealing that substitutional Cr enhances magnetism and that annealing reduces substitutional Cr, impacting magnetic behavior.

Contribution

It provides detailed microscopic analysis of Cr site occupancy and its correlation with magnetic properties in Ga1-xCrxN films, highlighting the importance of substitutional Cr for ferromagnetism.

Findings

Up to 90% of Cr occupies substitutional sites in films grown below 750°C.

Annealing at 825°C decreases substitutional Cr and ferromagnetic signal.

Cr site occupancy influences the magnetic properties of Ga1-xCrxN.

Abstract

Angular-dependent channeling Rutherford Backscattering Spectroscopy (c-RBS) has been used to quantify the fraction of Cr atoms on substitutional, interstitial, and random sites in epitaxial Ga1-xCrxN films grown by reactive molecular-beam epitaxy. The morphology of these films and correlation with their magnetic properties has been investigated. Films grown at temperatures below ~ 750oC have up to 90% of Cr occupying substitutional sites. Post-growth annealing at 825oC results in a systematic drop in the fraction of substitutional Cr as well as a fall off in the ferromagnetic signal. The roles of non-substitutional Cr in transferring charge from the Cr t2 band and segregation of substitutional Cr in the loss of magnetism are discussed. Overall, these results provide strong microscopic evidence that Cr-doped III-N systems are dilute magnetic semiconductors.