No abstract

Element-specific magnetic structures, particularly orbital magnetic moments, of spinel-type MnV 2 O 4 were investigated using X-ray magnetic circular dichroism (XMCD). X-ray absorption and XMCD spectra clearly reveal that the Mn 2+ (d 5 ) and V 3+ (d 2 ) states are coupled antiferromagnetically. Analyses of XMCD spectra using magneto optical sum rules revealed that small but finite orbital magnetic moments remain in both V and Mn 3d states, which accounts for the antiferro-type orbital ordering in the V sites of MnV 2 O 4 with coexisting complex and real orbital states. Additionally, the Cr doping effect in MnV 2 O 4 was examined. The XMCD spectra of Cr 3+ (d 3 ) L-edges exhibited the substitution of Cr ions to the V sites ferromagnetically, with low conductivity through the suppression of the orbital ordering.

Spinel-type vanadium oxides have been studied from the viewpoints of spin and orbital order in a geometrically frustrated system. We have investigated the doping effects of Cr 3+ (3d 3 ) and Mo 3+ (4d 3 ), which have no orbital degrees of freedom, to the V 3+ (3d 2 ) site of MnV 2 O 4 , in order to clarify the structural, transport and optical properties of Cr-and Mo-doped samples. The orbital order is suppressed by Cr and Mo doping and the electronic structure depends on the doped elements. The results of transport and optics indicate that electrons are localized in the Cr-doped system, while they become nearly itinerant in the Mo-doped one.