  In the present work, a thin film was deposited on quartz substrate by
reactive RF magnetron sputtering of high purity (99.999%) aluminium target
using ultra-high pure (Ar + N2) gas mixture. The percentage ratio of Ar and N2
in the gas mixture was 95% and 5%, respectively. Chemical characterization
using x-ray photoelectron spectroscopy (XPS) and energy-dispersive xray (EDX)
spectroscopy reveals that in the presence of dilute nitrogen, Al prefers to
react with residual oxygen to form Al2O3 while the nitrogen is incorporated in
it. The stoichiometry of bulk film is Al2N0.38O3.1. Magnetic and electrical
properties measurement shows that the film exhibits ntype dilute magnetic
semiconductor (DMS) property at 300K. The film has low electrical resistivity
of 6.3 {\Omega}-cm and high carrier mobility of 5.7*106 cm2V-1s-1 at 300K. A
density functional theory (DFT) calculation was performed to investigate the
origin of observed magnetism in the film. From first-principles calculation
based on DFT, it is found that for thermodynamic stability dilute nitrogen
incorporated in Al2O3 preferred to sit at the interstitial site, which is
responsible for observed magnetic property. Present study reported here
provides a new insight to prepare rarely observed n-type DMS at room
temperature by incorporating nitrogen interstitials in Al2O3, which is
desirable for potential application in the field of spintronics.
