Pressure-tuned magnetism and conductivity in pyrochlore iridates Lu2Ir2O7 and Er2Ir2O7
A2Ir2O7 iridates were proven to crystallise in the geometrically frustrated pyrochlore structure, which remains stable upon rare-earth cation substitution, temperature variation, and external pressure application. However, the change of interatomic distances and local distortions in the lattice frequently leads to complex electronic properties. The low-temperature behaviour in light-A iridates has been thoroughly investigated, including its evolution with pressure. The present pressure study reports the electrical transport and magnetotransport properties in heavy rare-earth Lu2Ir2O7 and Er2Ir2O7. Both compounds reveal a semiconductor-to-insulator transition induced by the antiferromagnetic ordering of the all-in-all-out (AIAO) type in the Ir sublattice. The transition monotonously shifts to a higher temperature under applied pressure by approximately 20 K at 3 GPa. As the transition in resistivity originates in the antiferromagnetic order, the latter is expected to be enhanced with the applied pressure as well. Upon cooling the compound in a magnetic field, the AIAO/AOAI domain structure with non-zero net magnetic moment is formed, mirroring itself in an asymmetric term in the magnetoresistance of Lu2Ir2O7. The application of pressure then enhances the asymmetric term. The same behaviour is proposed for the whole heavy rare-earth A2Ir2O7 series (A = Gd - Lu), although with magnetoresistance features masked significantly by a stronger response of magnetic A cations.