Complex magnetic properties in the mixed 4f−5d double perovskite iridates X2ZnIrO6(X=Nd,Sm,Eu,Gd)

Abstract

In this paper, we report on the synthesis and magnetic properties of a series of double perovskites $\mathit{Ln}{}_{2}{\mathrm{ZnIrO}}_{6}$ with $\mathit{Ln}$ = Nd, Sm, Eu, Gd. These compounds present examples of the rare case of double perovskites (general formula $A{}_{2}BB{}^{\ensuremath{'}}{\mathrm{O}}_{6}$) with a magnetic $4f$ ion on the $A$ site in combination with the strongly spin-orbit coupled 5d transition-metal ion ${\mathrm{Ir}}^{4+}$ on the $B$ sublattice. We discuss the impact of different rare earths on the macroscopic magnetic properties. ${\mathrm{Gd}}_{2}{\mathrm{ZnIrO}}_{6}$ and ${\mathrm{Eu}}_{2}{\mathrm{ZnIrO}}_{6}$ show ferrimagnetic or canted antiferromagnetic order below ${T}_{N}$ = 23 and 12 K, respectively. ${\mathrm{Sm}}_{2}{\mathrm{ZnIrO}}_{6}$ orders antiferromagnetically at ${T}_{N}$ = 13 K. ${\mathrm{Nd}}_{2}{\mathrm{ZnIrO}}_{6}$ exhibits more complex magnetic properties with a strong field dependence ranging from a two-step spin reorientation at ${\ensuremath{\mu}}_{0}H$ = 0.01 T to an antiferromagnetic ground state at intermediate external fields to a spin-flop phase for ${}_{0}H \ensuremath{\ge}$ 4 T. This unique behavior suggests an interesting interplay between ${\mathrm{Nd}}^{3+}$ and ${\mathrm{Ir}}^{4+}$. To further shed light on the relevant magnetic interaction, the zero-field magnetic ground state of ${\mathrm{Nd}}_{2}{\mathrm{ZnIrO}}_{6}$ is examined via neutron powder diffraction. In general, the magnetic properties of $\mathit{Ln}{}_{2}{\mathrm{ZnIrO}}_{6}$ hint towards a substantial contribution of the rare-earth ions and a significant correlation between $5d$ and $4f$ magnetism.