S = 1/2 square-lattice antiferromagnets: (CuX)LaB2O7 and (CuCl)A2B3O10 (X = Cl, Br; A = Ca, Sr; B = Nb, Ta)

Abstract

A series of magnetic compounds with the formula (CuX)LaB2O 7 and (CuCl)A2B3O10 (X = Cl, Br; A = Ca, Sr; B = Nb, Ta) have been prepared through a low-temperature topochemical route starting from nonmagnetic double- (n = 2) and triple- (n = 3) layered perovskites, respectively. The magnetic susceptibility of these compounds typically exhibits a broad maximum at low temperatures, characteristic of low-dimensional antiferromagnetic compounds. However, depending on the choice of the parameters, X, A, B and n, physical quantities such as the Weiss temperature and the temperature at a maximum susceptibility vary to a great extent, which enables us to study the phase diagram of the S = 1/2 frustrated square-lattice antiferromagnets (the so-called J1-J2 model). In particular, (CuCl)LaNb2O7, possibly having a ferromagnetic J1 and an antiferromagnetic J2, shows a spin-liquid behavior with the spin gap of 27 K.