Competing Magnetic Correlations on the Triangular Lattice

Abstract

ErMgGaO4 is a quantum antiferromagnet wherein pseudospin 1/2, Er3+ degrees of freedom decorate two-dimensional triangular planes separated by disordered nonmagnetic bilayers of Mg2+ and Ga3+. Its sister compound, YbMgGaO4, has attracted much interest as a quantum spin liquid ground state candidate, although the presence of the disordered Mg-Ga bilayers add complexity to this description. In contrast to YbMgGaO4, ErMgGaO4 shows a clear spin glass transition near Tg around 2 K, which is about 1/3 of its Curie-Weiss temperature. We have carried out new inelastic neutron scattering measurements on powder ErMgGaO4 samples, which show the frozen elastic component of the scattering to develop below Tg. The frozen (elastic) and fluctuating (inelastic) spin correlations are analysed separately, using a combination of linear spin wave theory and Warren line shape analysis. These are consistent with fluctuating 120◦ spin correlations at all temperatures, and the development of competing stripy static correlations below Tg.