SPIN-GLASS BEHAVIOR OF THE PEROVSKITE-RELATED COMPOUNDS, SRNLACURUON+5 (N = 1, 2, 3)

The magnetic properties of SrnLaCuRuOn+5 (n = 1, 2, 3) have been investigated by dc susceptibility measurements in the temperature range 6 K less-than-or-equal-to T less-than-or-equal-to 300 K. SrLaCuRuO6 has a simple orthorhombic perovskite structure whereas Sr3LaCuRuO8 and Sr2LaCuRuO7 adopt the 2D K2NiF4 and the intermediate Ruddlesden-Popper structures. At low temperatures the dc susceptibility data show sharp cusps and a divergence between the zero-field-cooled and field-cooled susceptibilities, characteristic of spin-glass behaviour. The spin-glass properties of these compounds can be ascribed to the competition between the nearest-neighbour and next-nearest-neighbour superexchange interactions. The progressive change in properties, with respect to the decrease in the dimensionality of the crystal structures, is also described. The thermoremanent magnetisation has been recorded as a function of temperature for SrLaCuRuO6 and two distinctive relaxation regimes have been observed. The high-temperature irreversibility in this compound is probably associated with blocking of uncompensated clusters. The time dependence of thermoremanent magnetisation has been also measured for SrLaCuRuO6 and the characteristic parameters are similar to those found in other insulating spin-glass systems.