Regensburg 2019 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 53: Frustrated Magnets - Strong Spin-Orbit Coupling (joint session TT/MA)

TT 53.6: Vortrag

Donnerstag, 4. April 2019, 10:45–11:00, Theater

Structural and magnetic properties of antifluorite (NH₄)₂IrCl₆: Candidate J_eff=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 J_eff=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 T_N=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 J_eff=1/2 picture. However, dilatometry shows a sharp drop in the length change along the <111> direction just below T_N. This indicates a possible lattice distortion at low temperature which may result in a deviation from the ideal J_eff=1/2 ground state. Magnetostriction measurements show that the field induced magnetization in the compound is strongly coupled to its lattice.