Anisotropy in the magnetic interaction and lattice-orbital coupling of single crystal Ni3TeO6

Anirudha Ghosh,C W Pao,Raman Sankar,X.-S Qiu,K.-H Chen,F C Chou,J F Lee,Sekhar C Ray,H M Tsai,Y Y Chin,W F Pong,H T Wang,Y C Shao,S H Hsieh,C H Du,J W Chiou,H J Lin

doi:10.1038/s41598-018-33976-w

Abstract

This investigation reports on anisotropy in the magnetic interaction, lattice-orbital coupling and degree of phonon softening in single crystal Ni3TeO6 (NTO) using temperature- and polarization-dependent X-ray absorption spectroscopic techniques. The magnetic field-cooled and zero-field-cooled measurements and temperature-dependent Ni L3,2-edge X-ray magnetic circular dichroism spectra of NTO reveal a weak Ni-Ni ferromagnetic interaction close to ~60 K (TSO: temperature of the onset of spin ordering) with a net alignment of Ni spins (the uncompensated components of the Ni moments) along the crystallographic c-axis, which is absent from the ab-plane. Below the Néel temperature, TN~ 52 K, NTO is stable in the antiferromagnetic state with its spin axis parallel to the c-axis. The Ni L3,2-edge X-ray linear dichroism results indicate that above TSO, the Ni 3d eg electrons preferentially occupy the out-of-plane 3d3z2−r2 orbitals and switch to the in-plane 3dx2−y2 orbitals below TSO. The inherent distortion of the NiO6 octahedra and anisotropic nearest-neighbor Ni-O bond lengths between the c-axis and the ab-plane of NTO, followed by anomalous Debye-Waller factors and orbital-lattice in conjunction with spin-phonon couplings, stabilize the occupied out-of-plane (3d3z2−r2) and in-plane (3dx2−y2) Ni eg orbitals above and below TSO, respectively.

Highlights

TN~ 52 K, NTO is stable in the antiferromagnetic state with its spin axis parallel to the c-axis
Deshpande et al.[20] found temperature- and substrate-driven preferential electron occupancy of the Mn 3d eg orbital in La0.85Zr0.15MnO3 (LZMO) thin films epitaxially grown on SrTiO3 (STO) and MgO substrates
As the temperature is reduced from room temperature to below the magnetic transition temperature, the preferred orbital of the Mn 3d eg state changes from the in-plane 3dx2−y2 to the out-of-plane d3z2−r2 orbital for LZMO/STO and vice versa for LZMO/MgO owing to the nature of the strain between the epitaxial film and the substrate

Summary

Results and Discussion

The different magnetization features revealed by the H// c and H⊥ c curves below TN (~52 K) suggest that the AFM spin axis is primarily parallel to the c-axis[12]. Upon cooling below TSO, the sign of the XLD spectra is reversed to positive, suggesting that the Ni eg holes preferentially occupy the out-of-plane 3d3z2−r2 (that is, preferential occupancy of the Ni eg electrons in 3dx2−y2) orbitals This result is reproducible and consistent with similar temperature-dependent Ni L3,2-edge XANES and corresponding XLD measurements with electrically polarized X-rays on a different beamline [BL-20A at the NSRRC (not presented here)]. At and below TSO, a large static distortion of the NiO6 octahedra (tensile-like strain due to the compression of the Ni-O bond length projected out-of-plane) network around the Ni sites, associated with phonon-softening behavior, stabilizes the preferential Ni eg electron occupation of the in-plane orbital (3dx2−y2) These strong anisotropic lattice-orbital and spin-phonon couplings are responsible for the evolution of anisotropic magnetic properties and orbital switching in the NTO single crystal

Methods

Author Contributions

Additional Information