Pressure-dependent dimerization in novel iridates AIrO3 (A = Mg, Zn)

Magnetism of Ir4+ compounds hinges upon their proximity to a dimerization instability that binds unpaired electrons into Ir-Ir bonds and renders the system non-magnetic. We propose temperature-dependent high-pressure XRD measurements that will explore this dimerization instability in MgIrO3 and ZnIrO3, two novel compounds prepared from the previously known beta-Li2IrO3. This parent compound becomes dimerized under pressure of several GPa, but MgIrO3 shows partial dimerization already at ambient pressure, despite its larger unit cell volume that nominally corresponds to a negative pressure applied to beta-Li2IrO3. Experimental information on the temperature dependence of the dimerization transition, phase coexistence upon the transition, and the structure of the dimerized phase will be used to understand the origin of this transformation that controls magnetism of iridates.