Temperature and Polarization Dependent X-Ray Spectroscopic Studies of Ni3TeO6 Single Crystals.
Anirudha Ghosh1*, K.-H. Chen1, X.-S. Qiu1, S. H. Hsieh1, Y. C. Shao1, C. H. Du1, H. T. Wang2, H. M. Tsai3, C.W. Pao3, H. J. Lin3, J. F. Lee3, W. F. Pong1
1Department of Physics, Tamkang University, Tamsui 251, Taiwan, Taiwan
2Department of Physics, National Tsinghua University, Hsinchu 300, Taiwan
3National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan
* Presenter:Anirudha Ghosh, email:ani.ghosh1985@gmail.com
The manipulation and understanding the correlation between electronic and magnetic ordering with applied electric fields continues to be one of the most acute challenges in condensed matter physics. In the quest to understand the interplay between electronic degrees of freedom, here we report the temperature dependence of anisotropic electronic and magnetic structures of Ni3TeO6 (NTO) single crystalline samples by means of the x-ray absorption spectroscopic techniques. NTO crystallizes in a non-centosymmetric, rhombohedral lattice and has three in-equivalent Ni sites (NiI, NiII and NiIII) which have both ferromagnetic (FM) and anti-ferromagnetic (AFM) interactions between them. Magnetic measurements and Ni L2,3-edge x-ray magnetic circular dichroism (XMCD) spectra have revealed an existence of weak Ni-Ni FM interaction (as a consequence of NiII-NiIII and NiI-NiII FM interaction) along the crystallographic c-axis, within a small temperature window, near ≈ 59 K, and completely absent in perpendicular-c direction. Below Néel Temperature, TN ≈ 52 K, the sample stabilizes in AFM state (as a consequence of NiIII-NiII, NiIII-NiI and NiI-NiIII AFM interactions) with the spin axis also parallel to the c-axis. The Ni L2,3-edge x-ray linear dichroism (XLD) plots have revealed contributions both from magnetic interactions (below the spin ordering temperature, TSO ≈ 59 K) and temperature independent crystal field effects, due to low symmetry trigonal crystal structure of NTO. The XLD results show that above TSO, the Ni 3d eg electrons will remain in in-plane 3dx2-y2 orbitals and switches to the out-of-plane 3d3z2-r2 orbitals below TSO. The ordering of Ni spins, below TSO, parallel to the c-axis stabilizes electron occupancy in 3d3z2-r2 orbitals via spin-orbit interaction. Our theoretical calculations, carried out in the framework of multiplet cluster calculations are consistent with the experimental XLD concerning the preferential electron occupancies in Ni 3d eg orbitals in the entire temperature range. Owing to the strong coupling between electronic structure and lattice, signatures of local lattice distortion have been found below TSO from the analyses of extended x-ray absorption fine structure spectra (EXAFS).

Keywords: x-ray linear dichroism, x-ray circular dichroism, orbital, spin and lattice correlation