A Nonfrustrated Magnetoelectric with Incommensurate
Magnetic Order in Magnetic Field¹

A. V. Syromyatnikov

Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg, 188300 Russia

e-mail: syromyat@thd.pnpi.spb.ru

Received February 19, 2007

Abstract—We discuss a model nonfrustrated magnetoelectric in which a sufficiently strong magnetoelectric
coupling produces an incommensurate magnetic order leading to ferroelectricity. Properties of the magneto-
electric 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 ferroelec-
tricity occurs at a field H_c1 that is lower than the saturation field H_c2. We have H_c1 = H_c2 at large enough mag-
netoelectric coupling. We show that at H = 0, ferroelectricity occurs at T = T_FE < T_N. A qualitative discussion
of the phase diagram in the H–T plane is presented within the mean-field approach.

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

DOI: 10.1134/S1063776107090154

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