NMR study of triangular lattice antiferromagnet Ba3CoSb2O9

Triangular lattice antiferromagnet has been an intensely studied topic in condensed matter physics for decades, and there are a sea of relevant theory papers, researching every detail of the triangular lattice system with antiferromagnetic interaction. In contrast, the experimental work has been largely limited by the difficulty in synthesizing high quality materials with triangular lattice. The Ba3CoSb2O9 compound thus has its own significance because it possesses a spin-1/2 triangular plane that is almost isotropic, which makes it a good research subject to experimentally verify many theoretical predictions. The fact that this compound has a saturation field of roughly 30T makes it possible for the exploration of the whole H-T phase diagram. The magnetization measurements on this compound revealed the existence of an up-up-down phase, which is of primary interest for the study of triangular lattice antiferromagnet, and the thermodynamics data sketched the H-T phase diagrams for both B//ab and B//c directions. However, these measurements were based on bulk properties and are not enough to determine the details of spin configuration. The nuclear magnetic resonance (NMR) experiment has the advantage as a local probe technique, and it can help discover the spin orientation by detecting the interaction of nuclear spins with nearby electron spins.Our NMR experiment was conducted in UCLA for low field (<12T) measurements and in NHMFL for high field (13