Eur. Phys. J. B 9, 187-199 (1999)
https://doi.org/10.1007/s100510050756

Quantum theory of the magneto-optical effect induced by Ni²⁺ ions in barium ferrites

¹ Department of Physics, Nanjing University, Nanjing 210008, and Department of Physics, Teacher's College, Yangzhou University, Yangzhou 225002, P.R. China
² CCAST (World Laboratory), PO Box 8730, Beijing 100080, and Department of Physics, Nanjing University, Nanjing 210008, and National Key Laboratory of Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, P.R. China
³ Laboratoire des Champs Magnétiques Intenses, CNRS/MPI, B.P. 166, 38042 Grenoble Cedex 9, France

Received: 7 January 1998
Published online: 15 May 1999

Abstract

To reveal the physical origin of the giant magneto-optical enhancement of Ni²⁺ ions in barium ferrite, quantitative calculations of the contributions of both the intra-ionic electric dipole transition between the and configurations of the Ni²⁺ ions and the intra-ionic electric dipole transition induced by odd-parity crystal field terms are presented. It is deduced that the transition is important in the origin of the considered magneto-optical enhancement. The most important factor is the Ni-Fe superexchange interaction; since it is strong enough, the Faraday rotation produced by the Ni²⁺ ions is large though the energy difference between the and configurations is large. It is demonstrated that though the intra-ionic electric dipole transition does produce Faraday rotation peaks in the visible range, their magnitude is too small to explain the observed Faraday rotation. The effect of the spin-orbit interaction on the Faraday rotation is analysed. The spin-orbit interaction of the ground configuration plays a very important role in the occurrence of Faraday effects, but the Faraday rotation does not increase linearly with the strength of the spin-orbit coupling. On the contrary, the spin-orbit interaction of the excited configuration has almost no effect on the Faraday rotation. It is shown that the mixing of the different multiplets of the ground term induced by the crystal field has a great influence on the magneto-optical properties.