Cr- and Mo-Doping Effects on Structural and Orbital Order Phase Transition in Spinel-Type MnV₂O₄

Abstract

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.

Investigating Orbital Magnetic Moments in Spinel-Type MnV2O4 Using X-ray Magnetic Circular Dichroism

“…Details of the sample preparation and the fundamental physical properties are provided in Ref. 11. The magnetic and orbital ordering temperatures of MnV 2 O 4 were estimated to be 59 and 54 K, respectively.…”

“…The orbital degeneracy of d 2 systems in octahedrally coordinated TM 3d t 2g orbitals allows for the controllability of orbital states through local lattice distortion. Interesting physics in the long-range orbital ordering using the Jahn-Teller active d 2 electrons in V 3+ states has been extensively investigated for AV 2 O 4 (A: Zn, Cd, Mg), [4][5][6] MnV 2 O 4 , [7][8][9][10][11] and FeV 2 O 4 . 12,13) MnV 2 O 4 is a good candidate for studying orbital ordering since the orbital magnetic moments of Mn 2+ (d 5 ) are nearly quenched with relatively large spin moments in high spin states.…”

“…Recently, Hemmi et al 11) reported that Cr or Mo impurities in MnV 2 O 4 suppressed the orbital ordering owing to the t 2g orbitals being fully occupied. We examined if the Cr 3+ or Mo 3+ impurities (d 3 ) substituted the V 3+ sites with additional electron numbers, resulting in metallic conductivity.…”

Local electronic and magnetic properties of ferro-orbital-ordered FeV2O4

“…4) The orbital degeneracy of 3d 2 systems in octahedrally coordinated TM 3d t 2g orbitals allows for the controllability of orbital states through local lattice distortion. Interesting physics in the long-range orbital ordering using the Jahn-Teller active d 2 electrons in V 3+ states has been extensively investigated for AV 2 O 4 (A; Zn, Cd, Mg), [5][6][7] MnV 2 O 4 , [8][9][10][11][12] and FeV 2 O 4 13,14) with their mixed-valence-type Fe 1−x Mn x V 2 O 4 , 15,16) and CoV 2 O 4 . 17,18) In the case of MnV 2 O 4 , orbital magnetic moments of Mn 2+ (d 5 ) are nearly quenched with relatively large spin moments in high spin states.…”