Fig. 1.

Crystal structure and anisotropic magnetic behavior of γ-lithium iridate. a, b Magnetic anisotropy, represented by τ/H, as a function of magnetic field H in the bc- and hc-planes at 4 K. A sharp and highly anisotropic feature defined as H ^* marks the suppression of long-range magnetic order and entry into a spin-fluid state. The angle θ in the legend is defined between the external magnetic field direction and the ab-plane such that θ = 90° corresponds to magnetic field aligned along the c-axis in both data sets. c The three-dimensional crystal structure of γ-lithium iridate, comprised of two orientations of iridium honeycomb planes. The diamond-shaped schematic of the crystal morphology is a reflection of the crystal structure when viewed along the c-axis. The crystal is rotated in a, b with respect to the external magnetic field in the planes depicted by the white lines in c, which also illustrate the orientation of the bc- and hc- rotational planes with respect to the two interwoven honeycomb planes. The colors on the diamond represent the direction of the applied magnetic field with respect to the crystallographic directions (a = green, b = blue and c = red) for the measurements shown in a, b, with the color gradient mapping field direction for those angles between the principal directions. d τ/H as a function of temperature with magnetic field applied ~5° from the b-axis shows a crossover from a sharp transition to long-range order at fields below H ^* to a smooth change in torque that characterizes the onset of spin correlations at fields above H ^*