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MA: Fachverband Magnetismus
MA 40: Frustrated Magnets - Strong Spin-Orbit Coupling (joint session TT/MA)
MA 40.6: Talk
Thursday, April 4, 2019, 10:45–11:00, Theater
Structural and magnetic properties of antifluorite (NH4)2IrCl6: Candidate Jeff=1/2 Mott insulator — •Nazir Khan, Anton Jesche, and Alexander A. Tsirlin — EP VI, Institute of Physics, University of Augsburg, 86135 Augsburg, Germany
Ammonium hexachloroiridate, (NH4)2IrCl6, possesses a face centered cubic (fcc) lattice of the antifluorite K2PtCl6-type with isolated and regular IrCl6 octahedra at high temperatures. The lattice symmetry and the 5d magnetic ion (Ir4+) render realization of ideal Jeff=1/2 moment on the frustrated fcc lattice that has been predicted to host rich magnetic phases driven by Heisenberg and Kitaev exchanges. Using synchrotron X-ray powder diffraction and dilatometry, we investigate structural effects in (NH4)2IrCl6 at low temperatures and in applied magnetic fields. Magnetization measurements indicate long-range antiferromagnetic ordering sets in below TN=2.2 K. The field dependence of magnetization suggests a field induced magnetic phase transition at a critical field which depends on the crystallographic directions. The estimated effective magnetic moment seems consistent with the Jeff=1/2 picture. However, dilatometry shows a sharp drop in the length change along the <111> direction just below TN. This indicates a possible lattice distortion at low temperature which may result in a deviation from the ideal Jeff=1/2 ground state. Magnetostriction measurements show that the field induced magnetization in the compound is strongly coupled to its lattice.