### Abstract

We investigate the spin induced polarization in the multiferroic compound Ba _{2}CoGe _{2}O _{7} using variational and finite-temperature mean field approaches, with the aim to reproduce the peculiar behavior of the induced polarization in a magnetic field observed experimentally in Murakawa. The compound is usually described by a spin-3/2 Heisenberg model extended with easy-plane anisotropy and Dzyaloshinskii-Moriya (DM) interaction. By applying a magnetic field parallel to the [110] axis, three phases can be distinguished in this model: (i) At high magnetic field, we find a partially magnetized phase with spins parallel to the fields and uniform polarization. (ii) Below a critical field, the ground state is a twofold-degenerate canted antiferromagnet, where the degeneracy can be lifted by a finite DM interaction. (iii) At zero field, a U(1) symmetry-breaking phase takes place, exhibiting a Goldstone mode. We find that extending the Hamiltonian with an antiferroelectric term results in the appearance of a canted ferrimagnetic phase for h 1 T. This phase is characterized by a finite staggered polarization, as well as by a magnetization closing a finite angle with the applied field leading to torque anomalies.

Original language | English |
---|---|

Article number | 224419 |

Journal | Physical Review B - Condensed Matter and Materials Physics |

Volume | 84 |

Issue number | 22 |

DOIs | |

Publication status | Published - Dec 20 2011 |

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### ASJC Scopus subject areas

- Condensed Matter Physics
- Electronic, Optical and Magnetic Materials

### Cite this

_{2}CoGe

_{2}O

_{7}: Effect of the antiferroelectric coupling.

*Physical Review B - Condensed Matter and Materials Physics*,

*84*(22), [224419]. https://doi.org/10.1103/PhysRevB.84.224419

**Zero- and finite-temperature mean field study of magnetic field induced electric polarization in Ba _{2}CoGe _{2}O _{7} : Effect of the antiferroelectric coupling.** / Romhányi, Judit; Lajkó, Miklós; Penc, K.

Research output: Contribution to journal › Article

_{2}CoGe

_{2}O

_{7}: Effect of the antiferroelectric coupling',

*Physical Review B - Condensed Matter and Materials Physics*, vol. 84, no. 22, 224419. https://doi.org/10.1103/PhysRevB.84.224419

_{2}CoGe

_{2}O

_{7}: Effect of the antiferroelectric coupling. Physical Review B - Condensed Matter and Materials Physics. 2011 Dec 20;84(22). 224419. https://doi.org/10.1103/PhysRevB.84.224419

}

TY - JOUR

T1 - Zero- and finite-temperature mean field study of magnetic field induced electric polarization in Ba 2CoGe 2O 7

T2 - Effect of the antiferroelectric coupling

AU - Romhányi, Judit

AU - Lajkó, Miklós

AU - Penc, K.

PY - 2011/12/20

Y1 - 2011/12/20

N2 - We investigate the spin induced polarization in the multiferroic compound Ba 2CoGe 2O 7 using variational and finite-temperature mean field approaches, with the aim to reproduce the peculiar behavior of the induced polarization in a magnetic field observed experimentally in Murakawa. The compound is usually described by a spin-3/2 Heisenberg model extended with easy-plane anisotropy and Dzyaloshinskii-Moriya (DM) interaction. By applying a magnetic field parallel to the [110] axis, three phases can be distinguished in this model: (i) At high magnetic field, we find a partially magnetized phase with spins parallel to the fields and uniform polarization. (ii) Below a critical field, the ground state is a twofold-degenerate canted antiferromagnet, where the degeneracy can be lifted by a finite DM interaction. (iii) At zero field, a U(1) symmetry-breaking phase takes place, exhibiting a Goldstone mode. We find that extending the Hamiltonian with an antiferroelectric term results in the appearance of a canted ferrimagnetic phase for h 1 T. This phase is characterized by a finite staggered polarization, as well as by a magnetization closing a finite angle with the applied field leading to torque anomalies.

AB - We investigate the spin induced polarization in the multiferroic compound Ba 2CoGe 2O 7 using variational and finite-temperature mean field approaches, with the aim to reproduce the peculiar behavior of the induced polarization in a magnetic field observed experimentally in Murakawa. The compound is usually described by a spin-3/2 Heisenberg model extended with easy-plane anisotropy and Dzyaloshinskii-Moriya (DM) interaction. By applying a magnetic field parallel to the [110] axis, three phases can be distinguished in this model: (i) At high magnetic field, we find a partially magnetized phase with spins parallel to the fields and uniform polarization. (ii) Below a critical field, the ground state is a twofold-degenerate canted antiferromagnet, where the degeneracy can be lifted by a finite DM interaction. (iii) At zero field, a U(1) symmetry-breaking phase takes place, exhibiting a Goldstone mode. We find that extending the Hamiltonian with an antiferroelectric term results in the appearance of a canted ferrimagnetic phase for h 1 T. This phase is characterized by a finite staggered polarization, as well as by a magnetization closing a finite angle with the applied field leading to torque anomalies.

UR - http://www.scopus.com/inward/record.url?scp=84855306766&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84855306766&partnerID=8YFLogxK

U2 - 10.1103/PhysRevB.84.224419

DO - 10.1103/PhysRevB.84.224419

M3 - Article

AN - SCOPUS:84855306766

VL - 84

JO - Physical Review B-Condensed Matter

JF - Physical Review B-Condensed Matter

SN - 0163-1829

IS - 22

M1 - 224419

ER -