Complex magnetic properties in the mixed 4f -5d double perovskite iridates Ln2ZnIrO6 (Ln = Nd, Sm, Eu & Gd)

In this work, we report on the synthesis and magnetic properties of a series of double perovskites Ln\(_2\)ZnIrO\(_6\) with Ln = Nd, Sm, Eu & Gd. These compounds present new examples of the rare case of double perovskites (general formula A\(_2\)BB'O\(_6\)) with a magnetic 4f -ion on the A-site in combination with the strongly spin-orbit coupled 5d-transition metal ion Ir\(^{4+}\) on the B-sublattice. We discuss the impact of different rare earths on the macroscopic magnetic properties. Gd\(_2\)ZnIrO\(_6\) and Eu\(_2\)ZnIrO\(_6\) show weak canted antiferromagnetic order below T\(_N\) = 23 K and T\(_N\) = 12 K, respectively. Sm\(_2\)ZnIrO\(_6\) orders antiferromagnetically at T\(_N\) = 13 K. Nd\(_2\)ZnIrO\(_6\) exhibits complex magnetic properties with strong field dependence ranging from a two-step behavior at H = 0.01 T to an antiferromagnetic ground state at intermediate external fields and a spin-flop phase at H\(\geq\)4 T, which suggests complex interplay between Nd\(^{3+}\) and Ir\(^{4+}\) . To further shed light on this magnetic interaction, the magnetic structure of Nd\(_2\)ZnIrO\(_6\)'s ground state is examined via neutron powder diffraction.