Small moments without long-range magnetic ordering in the zero-temperature ground state of the double-perovskite iridate Ba₂YIrO₆

The spin-orbit coupled double perovskite iridate Ba₂YIrO₆ with d⁴ occupancy of Ir is considered as a candidate material for a non-magnetic J = 0 ground state. The issue of existence of such a state in Ba₂YIrO₆ however has opened up intense debates both in experimental and theoretical studies. In this study, we revisit the issue using ab-initio density functional combined with dynamical mean field theory to investigate the magnetic properties of Ba₂YIrO₆ down to zero temperature. To reach the ground state, a recently developed impurity solver based on tensor-product states working directly at zero temperature is employed. We find that Ba₂YIrO₆ has a small non-zero magnetic moment, both at T = 0 K as well as at room temperature. We did not observe any evidence of magnetic ordering, not even at T = 0 K. We argue that the small moments in combination with small exchange couplings lead to many possible magnetic ordering patterns, whose ground state energies differ just by a few meV. As a result, this configurational frustration prevents the system from realizing one of the possible ordering patterns.