Magnetic structure of low-dimensional LiCu 2 O 2 multiferroic according to 63,65 Cu and 7 Li NMR studies
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ISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Magnetic Structure of LowDimensional LiCu2O2 Multiferroic according to 63,65Cu and 7Li NMR Studies A. F. Sadykova, A. P. Gerashchenkoa, Yu. V. Piskunova, V. V. Ogloblicheva, A. G. Smol’nikova, S. V. Verkhovskiia, A. Yu. Yakubovskiib, E. A. Tishchenkoc, and A. A. Bushd aInstitute
of Metal Physics, Ural Division, Russian Academy of Sciences, ul. S. Kovalevskoi 18, Yekaterinburg, 620990 Russia email: [email protected] bNational Research Centre Kurchatov Institute, pl. Akademika Kurchatova 1, Moscow, 123182 Russia c Kapitza Institute for Physical Problems, Russian Academy of Sciences, ul. Kosygina 2, Moscow, 119334 Russia dMoscow State Technical University of Radio Engineering, Electronics, and Automation, pr. Vernadskogo 78, Moscow, 119454 Russia Received March 11, 2012
Abstract—The complex NMR study of the magnetic structure of LiCu2O2 multiferroic has been performed. It has been shown that the spin spirals in LiCu2O2 are beyond the ab, bc, and ac crystallographic planes. The external magnetic field applied along the c axis of the crystal does not change the spatial orientation of spirals in Cu2+ chains. A magnetic field of H0 = 94 kOe applied along the a and b axes rotates the planes of spin spi rals in chains, tending to orient the normal n of spirals along the external magnetic field. The rotation angle of the planes of the magnetic moments are maximal at H0 || b. DOI: 10.1134/S1063776112090105
1. INTRODUCTION The LiCu2O2 multiferroic is a frustrated quasione dimensional magnetic material with competing ferro and antiferromagnetic exchange interactions between the nearestneighbor and nextnearestneighbor spins in the CuO2 chain, respectively. Such systems are interesting from the viewpoint of pure physics and are promising objects for possible microelectronic appli cations. Below the critical temperature TN = 23 K, the LiCu2O2 compound undergoes a transition to an ordered state characterized by the incommensurate spiral magnetic structure [1, 2], which is accompanied by the spontaneous appearance of the macroscopic electric polarization P [3]. The length and direction of the vector P depend on the external magnetic field. There are several different theories explaining the appearance of magnetoelectricity in compounds with the spiral magnetic structure [4–6]. They provide dif ferent predictions concerning the relation between the spatial orientation of the spin spiral and the direction of the electric polarization. For this reason, for the experimental test of existing theoretical models of magnetoelectricity, it is important to know the real spatial orientation of the planes of spin spirals in the crystal and its evolution depending on the magnitude and direction of the external magnetic field. Although the magnetic and electric properties of LiCu2O2 were investigated in a large number of works [1–3, 7–13], the magnetic structure of this oxide in the ground state is still unclear. In particular, using the
neutron diffraction data, Masuda et al. [1]
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