Magnetic correlation in the square-lattice spin system (CuBr)Sr2Nb3O10: A neutron diffraction study

Abstract

Magnetic correlation in the quantum S = 1/2 square-lattice system (CuBr)Sr 2 Nb 3 O 10 has been studied by neutron diffraction. A novel commensurate in-plane, helical antiferromagnetic (AFM) ordering, characterized by the propagation vector k = (0 3/8 1/2), has been confirmed from the appearance of magnetic Bragg peaks below T N ∼ 7.5 K. The ordered moment at 2 K is found to be 0.79(7) μ B /Cu 2+ -ion. The observed helical AFM structure differs from the ground state predicted theoretically from the J 1 -J 2 model as well as from experimentally reported states for other quantum S = 1/2 square-lattice systems. However, the observed helical magnetic structure can be described in a J 1 -J 2 -J 3 model. Under a 4.5 T magnetic field, the spin-order changes drastically and is characterized by the propagation vector k 1 = (0 1/3 0.446) and a probable k 2 = (0 0 0) vector.

Field-induced evolution of magnetic ordering in the quantum spin system (CuBr)Sr2Nb3O10with aRitter1, Yusuf2, Bera3 et al. 2013Phys. Rev. BSelf Cite6120View full textAdd to dashboardCite

“…Earlier preliminary neutron-diffraction data under a magnetic field of 4.5 T (corresponding to the 1 /3 magnetization plateau state) indicated the presence of a different magnetic propagation vector under the field without explaining the existence of the 1 /3 magnetization plateau. 6 In this paper, we present the results of a recent neutrondiffraction investigation under magnetic fields up to 10 T. The results clearly show that the magnetization plateau is induced by the competition between two field-induced magnetic phases (a ferromagnetic, F, phase and a AFM, AF2, phase with κ = [0 1 /3 γ ]) and is only coincidentally situated at M = 1 /3 M S .…”

“…Figure 3(a) displays parts of the difference pattern at 2 K recorded for magnetic fields of H = 0, 1, and 2.5 T. Magnetic peaks visible at 1 T are similar to those at zero field and correspond to the AF1 phase, with a magnetic propagation vector κ 1 = [0 3 /8 1 /2], already described in our previous paper. 6 The refinement using the same magnetic structure model as used in Ref. 6 for the zero-field data works nicely and results in a magnetic moment value of μ Cu = 0.75(2) μ B .…”

“…6 The refinement using the same magnetic structure model as used in Ref. 6 for the zero-field data works nicely and results in a magnetic moment value of μ Cu = 0.75(2) μ B . In this AF1 structure, spins are propagating in a cycloidal spiral within the Cu-Br layers with an AFM coupling between neighboring layers in c direction; for a picture of this magnetic structure, see Fig.…”

“…[1][2][3][4][5][6] Originally described in P 4/mmm, 7,8 the crystal structure of these compounds is characterized by square lattices of Cu 2+ ions in CuX-Halide layers separated by n slabs of nonmagnetic corner-sharing BO 6 octahedra. Interest in these compounds was stimulated as the compounds were believed to represent possible examples for the frustrated two-dimensional (2D) S = 1 /2 square lattice J 1 -J 2 model.…”

“…13 While magnetization plateaus at M = 1 /3 M S are predicted for lattices based on triangular symmetries, 14 the frustrated square lattice with S = 1 /2 should only allow a plateau at M = 1 /2 M S within the simple J 1 -J 2 model. 15 Our first study on this compound using neutron diffraction determined the zero-field magnetic structure below T N 1 = 7.5 K to consist of an antiferromagnetic (AFM) alignment of Cu spins within the CuBr layers (helical magnetic structure) with a magnetic propagation vector κ = [0 3 /8 1 /2] and a magnetic moment value of about μ Cu = 0.8(1) μ B at 2 K. 6 In order to explain the existence of the helical magnetic structure not foreseen in the J 1 -J 2 model, the J 1 -J 2 -J 3 was invoked. Interestingly enough, a 1 /3 plateau in the magnetization has been theoretically predicted within the J 1 -J 2 -J 3 model for J 1 = −1, J 2 = 1, and J 3 = 0.5 (see Ref.…”