Zero and finite temperature mean field study of magnetic field induced electric polarization in Ba2CoGe2O7

Details Zero and finite temperature mean field study of magnetic field induced electric polarization in Ba2CoGe2O7 Zero and finite temperature mean field study of magnetic field induced electric polarization in Ba2CoGe2O7

2011-10-04

arxiv.org/abs/1110.0788v1

Phys. Rev. B 84, 224419 (2011)

Physics

Condensed Matter

Strongly Correlated Electrons

9 pages, 8 figures

Scientific paper

10.1103/PhysRevB.84.224419

We investigate the spin-induced polarization in the multiferroic compound Ba2CuGe2O7 using variarional and finite temperature mean field approaches. The compound is described by a spin-3/2 Heisenberg model extended with easy plane anisotropy and Dzyaloshinskii-Moriya (DM) interaction. Applying magnetic field parallel to the [110] axis, three phases can be distinguished: (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. To reproduce the magnetization and polarization measurements reported in Murakawa et al. [Phys. Rev. Lett. 105, 137202 (2010)], we introduce an additional term in the Hamiltonian that couples the polarizations on neighboring tetrahedra. This results in the appearance of a canted ferrimagnetic phase for h < 1 T, characterized by a finite staggered polarization, as well as by a finite magnetization along the [-1,1,0] axis that leads to torque anomalies.

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