Evidence for room temperature ferromagnetism in the In1−xCrxN system

Despite considerable research on the nitride based dilute magnetic semiconductors (DMS) there is still considerable uncertainty as to the origin of the room temperature ferromagnetism, with clusters and precipitates suggested. We have studied chromium doped indium nitride (In1−xCrxN) with x varying from 0.005 to 0.04 and have observed room temperature ferromagnetic behaviour in all of our films with x > 0.01, with no evidence for chromium rich clusters visible in either XRD or scanning TEM, though the high mobility of the Cr within the growing film suggests that it is on interstitial sites. We also do not see a significant paramagnetic component in temperature dependent magnetisation measurements, which also suggests that any superparamagnetic behaviour due to chromium clusters is not a significant part of the magnetic behaviour. The magnitude of the ferromagnetic signal scales with the electron concentration in the film, rather than the chromium concentration, which may suggest that In1−xCrxN shows the electron based equivalent of the hole mediated ferromagnetism observed in Ga1−xMnxAs.