Magnetoelectric effect in mixed-valency oxides mediated by charge carriersV. A. Stephanovich1, M. D. Glinchuk2 and R. Blinc3
1 Opole University, Institute of Mathematics and Informatics - Opole, 45-052, Poland, EU
2 Institute for Problems of Materials Science, National Academy of Science of Ukraine Krjijanovskogo 3, 03142 Kiev, Ukraine
3 Josef Stefan Institute - Jamova 39, 1000 Ljubliana, Slovenia, EU
received 29 April 2008; accepted in final form 11 June 2008; published August 2008
published online 16 July 2008
We show that the presence of free carriers in a substance can generate the multiferroic behavior. Namely, if the substance has mixed-valence ions, which can supply free carriers and have electric dipole and spin moments, all three types of long-range order (ferromagnetic, ferroelectric and magnetoelectric (ME)) can occur at low temperature. The physical origin of the effect is that charge carriers can mediate the multiferroic behavior via spin-spin (RKKY), dipole-dipole and dipole-spin interactions. Our estimate of the interaction magnitude shows that there exist an optimal carrier concentration, at which the strength of ME interaction is maximal and comparable to that of spin-spin RKKY interaction. This permits to conclude that in substances, where RKKY interaction between local spins is not small, a substantial value of free-carriers-mediated ME interaction can occur. Our analysis shows that disorder in the above substances does not suppress multiferroic effects.
75.80.+q - Magnetomechanical and magnetoelectric effects, magnetostriction.
77.80.Bh - Phase transitions and Curie point.
75.50.Dd - Nonmetallic ferromagnetic materials.
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