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TT: Fachverband Tiefe Temperaturen

TT 18: CE: Low-dimensional Systems - Materials 1

TT 18.2: Vortrag

Montag, 14. März 2011, 18:45–19:00, HSZ 201

A microscopic magnetic model for the spin-1/2 Heisenberg piezoelectric ferrimagnet Cu₂OSeO₃ — •Oleg Janson, Alexander Tsirlin, and Helge Rosner — Max-Planck-Institut für Chemische Physik fester Stoffe

We present the results of band structure calculations for the piezoelectric ferrimagnet Cu₂OSeO₃. Below the T_C = 60 K, the compound exhibits sizable magnetocapacitance and stays metrically cubic, which excludes lattice strain from possible magnetoelastic mechanisms [1]. The crystal structure of Cu₂OSeO₃ comprises two inequivalent positions of magnetic Cu²⁺ atoms: 4 Cu(1) atoms are locally coordinated by a trigonal bipyramid of O atoms, while 12 Cu(2) atoms have a distorted 4-fold coordination, typical for cuprates. The net magnetization in the ferrimagnetically ordered ground state results from the antiparallel arrangement of Cu(1) and Cu(2) sublattices [2] and amounts to one-half of the saturation value. Based on DFT calculations, we disclose different magnetically active orbitals for Cu(1) and Cu(2) and five relevant magnetic couplings that form a complex, albeit non-frustrated 3D spin lattice. The role of quantum fluctuations will be discussed in the context of the reduced ordered moment on Cu atoms amounting to 0.61 µ_B [1] and a low T_C/J≈0.6.

[1] J.-W. G. Bos et al., Phys. Rev. B 78, 094416 (2008).

[2] M. Belesi et al., Phys. Rev. B 82, 094422 (2010).