Non-collinear antiferromagnetism of coupled spins and pseudospins in the double perovskite La2CuIrO6

TL;DR

This study uncovers complex non-collinear antiferromagnetic order in La2CuIrO6, driven by interactions between spin-1/2 Cu and pseudospin-1/2 Ir ions influenced by strong spin-orbit coupling and lattice symmetry.

Contribution

It provides a detailed experimental characterization of the magnetic structure and interactions in La2CuIrO6, highlighting the role of spin-orbit coupling and lattice effects in its magnetic behavior.

Findings

Strong coupling of Cu and Ir sublattices below 74 K

Non-collinear antiferromagnetic order with small transverse moment

Anomaly at 54 K indicating cooperative transverse moment ordering

Abstract

We report the structural, magnetic and thermodynamic properties of the double perovskite compound La2CuIrO6 from X-ray, neutron diffraction, neutron depolarization, dc magnetization, ac susceptibility, specific heat, muon-spin-relaxation (uSR), electron-spin-resonance (ESR) and nuclear magnetic resonance (NMR) measurements. Below ~113 K, short-range spin-spin correlations occur within the Cu2+ sublattice. With decreasing temperature, the Ir4+ sublattice progressively involves in the correlation process. Below T = 74 K, the magnetic sublattices of Cu (spin s = 1/2) and Ir (pseudospin j = 1/2) in La2CuIrO6 are strongly coupled and exhibit an antiferromagnetic phase transition into a non-collinear magnetic structure accompanied by a small uncompensated transverse moment. A weak anomaly in ac-susceptibility as well as in the NMR and {\mu}SR spin lattice relaxation rates at 54 K is interpreted as a cooperative ordering of the transverse moments which is influenced by the strong spin-orbit coupled 5d ion Ir4+. We argue that the rich magnetic behaviour observed in La2CuIrO6 is related to complex magnetic interactions between the strongly correlated spin-only 3d ions with the strongly spin-orbit coupled 5d transition ions where a combination of the spin-orbit coupling and the low-symmetry of the crystal lattice plays a special role for the spin structure in the magnetically ordered state.