Polariton spectrum of a bounded antiferromagnet with a center of antisymmetry in an external electric field oriented nor
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HYSICAL PROPERTIES OF CRYSTALS
Polariton Spectrum of a Bounded Antiferromagnet with a Center of Antisymmetry in an External Electric Field Oriented Normally to the Surface D. V. Kulagin, A. S. Savchenko, and S. V. Tarasenko Donetsk Physics and Engineering Institute, National Academy of Sciences of Ukraine, Donetsk, 83114 Ukraine email: [email protected] Received July 16, 2008
Abstract—The features of transmission of TE and TM polaritons through an interface between magnetic and nonmagnetic media and their localization at the interface in an external dc electric field have been studied. This field is directed along the hard magnetization axis. The magnetic medium is an easyplane tetragonal antiferromagnet; it is odd with respect to inversion. A magnetic plate and a 1D magnetic photonic crystal in an external dc electric field, oriented normally to the interface, are considered. PACS numbers: 75.70.i, 75.80.+q, 42.25.Gy, 42.70.Qs DOI: 10.1134/S1063774509070086
INTRODUCTION The possibility of influencing the character of the localization and dispersive properties of TE and TM polaritons in antiferromagnetic media with a center of antisymmetry using an external dc electric field has not been investigated until now. At the same time, we believe this subject to be urgent not only for fundamental sci ence, but also for practical applications. First of all, rather large values of the linear magnetoelectric interac tion constant have been experimentally found for these media. In addition, Turov [1] theoretically formulated the conditions under which an antiferromagnetic struc ture (odd with respect to inversion) can be formed in a system of tangentially magnetized ferromagnetic layers separated by nonmagnetic layers. This circumstance makes it possible to significantly increase the magneto electric interaction coefficient by optimizing the param eter of contacting magnetic and nonmagnetic media. One alternative version is the formation of an antiferro magnetic structure with a center of antisymmetry based on the combination of piezoelectric and piezomagnetic layers with a continuous acoustic interlayer contact. Within the twosublattice model of antiferromagnetic medium (M1,2 are the sublattice magnetization vectors; |M1| = |M2| = M0), the corresponding invariant in the thermodynamic potential can be written as [2–4] 2
(1) F me = – M 0 γ αβδ m α l β e δ . Here, γαβδ is the tensor of magnetoelectric con stants; m = (M1 + M2)/2M0 and l = (M1 – M2)/2M0 are the ferromagnetism and antiferromagnetism vec tors, respectively; and e = E/M0 is the normalized electric field vector. Quadratic magnetooptical interaction is known to exist in antiferromagnetic crystals, which is indepen dent of magnetic structure parity with respect to inver
sion. For example, in the collinear phase of an easy axis (OZ axis) twosublattice antiferromagnet, the quadratic magnetooptical interaction can be written as (λαβγδ is the magnetooptical tensor) [6]: F mo = – λ αβγδ l α l β E γ E δ . (2) With allowance for this circum
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