Collinear Order in Frustrated Quantum Antiferromagnet on Square Lattice (CuBr)LaNb₂O₇

Abstract

Magnetic susceptibility, heat capacity, high-field magnetization and neutron diffraction measurements have been performed on a two-dimensional S ¼ 1=2 square-lattice system (CuBr)LaNb 2 O 7 , prepared by a topotactic ion-exchange reaction of a nonmagnetic double-layered perovskite RbLaNb 2 O 7. (CuBr)LaNb 2 O 7 exhibits a second-order magnetic transition at 32 K, in marked contrast to a spin-singlet nature for its Cl-based counterpart (CuCl)LaNb 2 O 7 , despite nearly identical structural parameters. The magnetic structure is a novel collinear antiferromagnetic (CAF) ordering characterized by a modulation vector q ¼ ð; 0; Þ with a reduced moment of 0.6 B. Mixed ferromagnetic nearest-neighbor (J 1) and antiferromagnetic second-nearest-neighbor (J 2) interactions are of comparable strength (J 1 =k B ¼ À35:6 K and J 2 =k B ¼ 41:3 K), placing the system in a more frustrated region of the CAF phase than ever reported.

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

“…From the value of α, it is evident that this system is at the phase boundary between ordered collinear AFM (with a dominating AFM J 2 ) and disordered states in the theoretical phase diagram. [15][16][17][18][19] A collinear AFM structure [Q = (π 0) or (0 π )] was found for (CuBr)LaNb 2 O 7 , 43 an n = 2 member of the present Dion-Jacobson series [(CuX)A n−1 B n O 3n+1 ] with FM J 1 and an α value of (J 2 /J 1 = 41.3 K/(−35.6 K)) = 1.1, which is well inside the range for a collinear AFM state (α 0.6). The other reported square-lattice compounds with FM J 1 having a collinear AFM structure, such as Pb 2 VO(PO 4 ) 2 (α ∼ 1.6) 27 and BaCdVO(PO 4 ) 2 (α ∼ 0.9), 30 are as well far above the lower limit of α 0.6.…”

Muon spin relaxation studies of the frustrated quasi-two-dimensional square-lattice spin systemCu(Cl,Br)La(Nb,TaUemura1, Aczel2, Ajiro3 et al. 2009Phys. Rev. B292150View full textAdd to dashboardCite

“…A sister compound (CuBr)LaNb 2 O 7 orders into a collinear antiferromagnet (CLAF) below T N = 32 K, as shown by neutron scattering 13 and susceptibility measurements (Fig. 2).…”

Field-induced evolution of magnetic ordering in the quantum spin system (CuBr)Sr2Nb3O10with aRitter1, Yusuf2, Bera3 et al. 2013Phys. Rev. B6120View full textAdd to dashboardCite

“…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. 9,10 Recently it was shown, however, that the crystal structures of the n = 2 compounds (CuCl)LaNb 2 O 7 (Refs. 1 and 11), (CuBr)LaNb 2 O 7 (see Ref.…”