Complex magnetic ground state ofCuB2O4

Abstract

The magnetic ground-state of copper metaborate CuB 2 O 4 was investigated with unpolarized and polarized neutron scattering. A phase transition was found at T N ϭ21 K to a commensurate weakly ferromagnetic state followed by a second transition at T*ϭ10 K to an incommensurate magnetic structure. Neutron diffraction revealed a continuously changing magnetic propagation vector below T*, and unusually asymmetric magnetic satellite reflections. Additionally, diffuse scattering is observed in the temperature range 1.5 KрTр30 K. The magnetic structure determined in both phases are shown to be consistent with results of symmetry analysis. In particular, we find that only one of the two inequivalent Cu 2ϩ sublattice fully orders down to the lowest temperature. Our results show that the complex magnetic behavior of copper metaborate is a consequence of mutual interaction between the two Cu 2ϩ sublattices with different ordering temperatures.

Magnetic, structural, and dielectric properties ofCuB2O4

“…This change in the magnetic susceptibility has been shown to arise from a canted antiferromagnetic ordering. 2,5 These results are compatible with the reported magnetic point group 2 គ . 3 On further cooling, we observe a sharp increase of the magnetic susceptibilities at T N1 = 9 K. This transition has been shown to arise from an incommensurate spin structure.…”

“…3 On further cooling, we observe a sharp increase of the magnetic susceptibilities at T N1 = 9 K. This transition has been shown to arise from an incommensurate spin structure. 5 As reported earlier, we observe a strong anisotropy between measurement along the c tetragonal axis and the basal ͑a , b͒ plane. 2 This anisotropy is about 1 order of magnitude.…”

“…[1][2][3][4][5][6] Commensurate and incommensurate magnetic structures as well as frustration have been observed in this compound. Moreover, it has been reported that the Dzyaloshinskii-Moriya interactions 7 lead to the formation of a magnetic soliton lattice in this material.…”

“…3 The crystallographic and magnetic structure of CuB 2 O 4 was already investigated by x-ray and neutron diffractions and by specific-heat, magneticsusceptibility, magnetization, and muon-spin-rotation experiments. 2,5,6 CuB 2 O 4 crystallizes in a piezoelectric tetragonal I42d ͑n°122͒ space group ͑point symmetry 42m͒. The unit cell contains 12 f.u.…”

“…The ions at the 4b Wyckoff site are at the center of a square unit formed by four oxygen ions, while the ions at the 8d Wyckoff site are located near the center of a distorted oxygen octahedron. Below, T N2 = 21 K, a commensurate canted antiferromagnetic ordering appears, which is followed by an incommensurate and purely antiferromagnetic ordering below T N1 =9 K. 2,5 In this paper, we investigate the magnetic, structural, and dielectric properties of a CuB 2 O 4 single crystal. We measured the various properties along the main crystallographic axes ͑a, b, and c axes of the tetragonal symmetry͒.…”