Magnetic (Ga x Fe 1Àx ) 3 O 4 nanoparticles with 5%-33% gallium doping (x ¼ 0.05-0.33) were measured using x-ray absorption spectroscopy and x-ray magnetic circular dichroism to determine that the Ga dopant is substituting for Fe 3þ as Ga 3þ in the tetrahedral A-site of the spinel structure, resulting in an overall increase in the total moment of the material. Frequency-dependent alternating-current magnetic susceptibility measurements showed these particles to be weakly interacting with a reduction of the cubic anisotropy energy term with Ga concentration. The element-specific dichroism spectra show that the average Fe moment is observed to increase with Ga concentration, a result consistent with the replacement of A-site Fe by Ga.

Nanoparticles of VxFe3-xO4 with up to 33% vanadium doping (x=0 to 1) and a 9 nm diameter are investigated in order to determine the site preference of the vanadium and the magnetic behavior of the nanoparticles. The iron and vanadium L23-edge X-ray absorption spectroscopy (XAS) and Xray magnetic circular dichroism (MCD) spectra are used to identify that vanadium initially