Orbital and spin state of spinel oxide MnV$_{2}$O$_{4}$ investigated by NMR

Abstract

Spinel oxide MnV$_{2}$O$_{4}$ has a complex structural and magnetic properties such as orbital ordering, strong magnetic anisotropy and magnetostriction, due to the strong correlation between spin, orbital and lattice. The orbital and spin state, the important properties to understand strongly correlated system MnV$_{2}$O$_{4}$, were investigated by V and Mn NMR spectra measured with rotating the external magnetic field of 7 T.

The V$^{3+}$ ion, in the octahedral sites of the spinel structure, is related with the orbital ordering of MnV$_{2}$O$_{4}$. In order to observe orbital ordering directly, V NMR spectra were measured with rotating external magnetic field. The spectra show unique resonance frequency shift and peak splitting. The change in the anisotropic hyperfine field caused by the rotation of the electron spin reflects the spatial electron distribution (orbital state). Therefore the resonance frequency shift and the peak splitting can be originated from the orbital ordering. The resonance frequency shift and the peak splitting are not only caused by anisotropic hyperfine field due to orbital ordering but also by the dipole field originated from neighboring magnetic ions and magnetic anisotropy. This occurs in the rotation of the magnetic field because the angle between the magnetic moment and the magnetic field is an important factor to determine resonance frequency. To analyse the orbital and spin state exactly, the followings are calculated; the frequency shift caused by orbital ordering, the dipole field originated from the neighboring magnetic ions and the strong magnetic anisotropy are calculated in the rotation of the magnetic field.

The Mn NMR spectra, measured with rotating external magnetic field, also show a resonance frequency shift. The main reasons for the resonance frequency shift in the Mn NMR spectra are the dipole field originated from neighboring magnetic ions and the magnetic anisotropy because the Mn$^{...