Spin polarization of the magnetic spiral in NaCu_2O_2, as seen by NMR

The incommensurate (IC) spin ordering in quasi-1D edge-shared cuprate NaCu_2O_2 has been studied by ^{23}Na nuclear magnetic resonance spectroscopy in an external magnetic field near 6 Tesla applied along the main crystallographic axes. The NMR lineshape evolution above and below T_N\approx12 K yields a clear signature of an IC static modulation of the local magnetic field consistent with a Cu^{2+} spin spiral polarized in the bc-plane rather than in the ab-plane as reported from earlier neutron diffraction data.Comment: 5 pages, 4 figure

Microscopic Mechanisms of Spin-Dependent Electric Polarization in 3d Oxides

We present a short critical overview of different microscopic models for nonrelativistic and relativistic magnetoelectric coupling including the so-called "spin current scenario", ab-initio calculations, and several recent microscopic approaches to a spin-dependent electric polarization in 3d oxides. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2009.Financial support by the RFBR through Grants Nos. 07-02-96047, 08-02-00633 (A.S.M.), and by the DFG under contract DR269/3-1 (S.-L.D.) are acknowledged. A.S.M. would like to thank Leibniz-Institut f ̈ur Festk ̈orper- und Werkstoffforschung Dresden, where part of this work was done, for hospitality

Nonrelativistic Multiferroicity in the Nonstoichiometric Spin s=1/2 Spiral Chain Cuprate LiCu2O2

We argue for a recently observed puzzling multiferroic behavior in s=1/2 1D chain cuprate LiCu2O2 with edge-shared arrangement of CuO4 plaquettes and incommensurate spiral spin ordering can be consistently explained if one takes into account the nonrelativistic exchange-induced electric polarization on the Cu2+ centers substituting for the positions native for the Cu1+ ions. These substituent centers are proved to be an effective probe of the spin incommensurability and magnetic field effects.Comment: 4 pages, 4 figure

Multiferroicity Due to Nonstoichiometry in the Chain Cuprate LiVCuO 4

The recently observed multiferroic behavior in the s=1/2 chain cuprate LiVCuO4 (≡LiCuVO4) with edge-shared CuO4 plaquettes and helical spin ordering does not agree with the existing theories such as a spin-current scenario. We argue that the effect can be consistently explained, if the exchange-induced electric polarization on the out-of-chain Cu2+ centers substituting for Li ions in LiVCuO4 is taken into account. These substituent centers are proved to be an effective probe of the spin incommensurability and the magnetic-field effects. © Europhysics Letters Association.The DFG and RFBR Grants (Nos. 06-02-17242 and 07-02-96047) are acknowledged for financial support

Comment on "Competition between helimagnetism and commensurate quantum spin correlations in LiCu2O2"

The microscopic origin of the recently observed helical structure in LiCu2O2 [1] is considered. It is shown that the frustrated antiferromagnetic double chain scenario adopted in Ref.1 is unrealistic. It should be replaced by a frustrated single-chain (CuO2) scenario proposed in Ref. 2 with ferromagnetic nearest neighbor and antiferromagnetic next nearest neighbor exchange integrals \. [1] T. Masuda et al. Phys. Rev. Lett. 92 (2004), 177201. [2] A. Gippius et al. Phys. Rev. B 70 (2004), R01426; cond-mat/0312576.Comment: one page, one figur

Nonrelativistic Multiferrocity in the Nonstoichiometric Spin- 1 2 spiral-chain Cuprate LiCu2 O2

Puzzling multiferroic behavior observed recently in spin-1/2 one-dimensional chain cuprate LiCu2 O2 with edge-shared arrangement of CuO4 plaquettes and incommensurate spiral spin ordering is consistently explained to be a result of the nonrelativistic exchange-induced electric polarization on the Cu2+ centers substituting for the positions native for the Cu1+ ions. These substituent centers are proven to be an effective probe of the spin incommensurability and magnetic field effects. © 2009 The American Physical Society.The authors thank A. Loidl, U. Rößler, K. Dörr, R. Kuzian, and H. Rosner for discussions. The DFG and RFBR grants (No. 06-02-17242, No. 07-02-96047, and No. 08-02-00633) are acknowledged for financial support

NMR and LDA evidence for spiral magnetic order in the chain cuprate LiCu2O2

We report on {6,7}Li nuclear magnetic resonance measurements of the spin-chain compound LiCu2O2 in the paramagnetic and magnetically ordered states. Below T about 24 K the NMR lineshape presents a clear signature of incommensurate (IC) static modulation of the local magnetic field consistent with an IC spiral modulation of the magnetic moments. {7}Li NMR reveals strong phason-like dynamical fluctuations extending well below 24 K. We hypothesize that a series of phase transitions at 24.2, 22.5, and 9 K reflects a "Devil's staircase" type behavior generic for IC systems. LDA based calculations of exchange integrals reveal a large in-chain frustration leading to a magnetical spiral.Comment: 4 pages, 4 figure

Microscopic mechanisms of spin-dependent electric polarization in 3d oxides

We present a short critical overview of different microscopic models for nonrelativistic and relativistic magnetoelectric coupling including the so-called "spin current scenario", ab-initio calculations, and several recent microscopic approaches to a spin-dependent electric polarization in 3d oxides.Comment: 8 pages, 3 figure

7Li NMR study of the ordering phenomena in the intrinsic two-component magnetoelectric material Li2ZrCuO4

We report an experimental and theoretical study of the low temperature 7Li nuclear magnetic resonance (NMR) spectra of oriented powder samples of γ-Li2ZrCuO4 (≡Li2CuZrO4) which comprises interpenetrating sublattices of frustrated quasi-one- dimensional s=1/2 quantum Heisenberg magnetic Cu2+ chains and frustrated quantum Ising electric sublattice of LiI ions. Incommensurate spin order occurring in this compound at TNâ6 K gives rise to a drastic change of the 7Li NMR spectrum. We show that the peculiar NMR line shapes are determined by the specific, sample dependent, distribution of the LiI ions in the glassy ordered electric sublattice. The analysis of the NMR data in the framework of a spin-spiral model gives evidence for a remarkable interaction between magnetic and electric degrees of freedom in γ-Li2ZrCuO4, which suggests it as a promising model compound for fundamental studies of complex magnetoelectric phenomena and illustrates well their richness. © 2013 American Physical Society