1/3 magnetization plateau in spin-1/2 square lattice antiferromagnet (CuBr)Sr2Nb3O10

A new triple-layered perovskite (CuBr)Sr2Nb3O10 with the S = 1/2 square lattice has been prepared through a chimie douce route. Presence of strong spin frustration is inferred from zero-field specific heat measurements which exhibit successive phase transitions at 9.3 and 7.5 K. Application of magnetic fields merges the transition temperatures at 3 T, suggesting that the intermediate phase is of magnetic origin with fluctuating spin-spin correlation. Despite the square geometry, magnetization curves have revealed a metamagnetic transition to a novel phase characterized by a 1/3 plateau of the saturated magnetization.