NONFRUSTRATED MAGNETOELECTRIC WITH INCOMMENSURATE MAGNETIC ORDER IN THE MAGNETIC FIELD
Syromyatnikov A.V.

Поступила в редакцию: 19 Февраля 2007

PACS: 75.80.+q, 71.70.Ej, 77.80.-e

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We discuss a model nonfrustrated magnetoelectric in which a sufficiently strong magnetoelectric coupling produces an incommensurate magnetic order leading to ferroelectricity. Properties of the magnetoelectric in the magnetic field directed perpendicular to the wave vector describing the spin helix are considered in detail. Analysis of the classical energy shows that in contrast to the naive expectation, the onset of ferroelectricity occurs at a field H_c1 that is lower than the saturation field H_c2. We have H_c1=H_c2 at large enough magnetoelrctric coupling. We show that at H=0, ferroelectricity occurs at T=T_FEN. A qualitative discussion of the phase diagram in the H-T plane is presented within the mean-field approach.