Optical response of ferromagnetic YTiO3 studied by spectral ellipsometry

N. N. Kovaleva, A. V. Boris, P. Yordanov, A. Maljuk, E. Brücher, J. Strempfer, M. Konuma, I. Zegkinoglou, C. Bernhard, A. M. Stoneham, and B. Keimer
Phys. Rev. B 76, 155125 – Published 26 October 2007

Abstract

We have studied the temperature dependence of spectroscopic ellipsometry spectra of an electrically insulating, nearly stoichiometric YTiO3 single crystal with ferromagnetic Curie temperature TC=30K. The optical response exhibits a weak but noticeable anisotropy. Using a classical dispersion analysis, we identify three low-energy optical bands at 2.0, 2.9, and 3.7eV. Although the optical conductivity spectra are only weakly temperature dependent below 300K, we are able to distinguish high- and low-temperature regimes with a distinct crossover point around 100K. The low-temperature regime in the optical response coincides with the temperature range in which significant deviations from a Curie-Weiss mean-field behavior are observed in the magnetization. Using an analysis based on a simple superexchange model, the spectral weight rearrangement can be attributed to intersite di1dj1di2dj0 optical transitions. In particular, Kramers-Kronig consistent changes in optical spectra around 2.9eV can be associated with the high-spin-state (T13) optical transition. This indicates that other mechanisms, such as weakly dipole-allowed pd transitions and/or exciton-polaron excitations, can contribute significantly to the optical band at 2eV. The recorded optical spectral weight gain of the 2.9eV optical band is significantly suppressed and anisotropic, which we associate with complex spin-orbit-lattice phenomena near the ferromagnetic ordering temperature in YTiO3.

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  • Received 9 May 2007

DOI:https://doi.org/10.1103/PhysRevB.76.155125

©2007 American Physical Society

Authors & Affiliations

N. N. Kovaleva1, A. V. Boris1, P. Yordanov1, A. Maljuk1, E. Brücher1, J. Strempfer1, M. Konuma1, I. Zegkinoglou1, C. Bernhard2, A. M. Stoneham3, and B. Keimer1

  • 1Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
  • 2Department of Physics, University of Fribourg, Chemin du Musée 3, CH-1700 Fribourg, Switzerland
  • 3Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom

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Issue

Vol. 76, Iss. 15 — 15 October 2007

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