Magnetic structures of the iridium-based double perovskites Pr2NiIrO6 and Nd2NiIrO6 reinvestigated using neutron diffraction

Abstract

The magnetic structures of the double perovskites ${\mathrm{Pr}}_{2}{\mathrm{NiIrO}}_{6}$ and ${\mathrm{Nd}}_{2}{\mathrm{NiIrO}}_{6}$ have been reinvestigated using high-intensity neutron power diffraction and compared with previously published results by Kayser et al. [Acta Mater. 207, 116684 (2021)] and Ferreira et al. [Phys. Rev. Mat. 5, 064408 (2021)]. The strongly enhanced statistics of neutron diffraction data used in this paper help us to disentangle the complicated coexisting magnetic orderings of the three sublattices in ${\mathrm{Pr}}_{2}{\mathrm{NiIrO}}_{6}$ and ${\mathrm{Nd}}_{2}{\mathrm{NiIrO}}_{6}$. A mainly ferrimagnetic ordering with additional antiferromagnetic components with propagation vector $k=0$ has been confirmed in both ${\mathrm{Pr}}_{2}{\mathrm{NiIrO}}_{6}$ and ${\mathrm{Nd}}_{2}{\mathrm{NiIrO}}_{6}$ compounds below the magnetic orderings ${T}_{C}=110$ and 120 K, respectively. ${\mathrm{Nd}}_{2}{\mathrm{NiIrO}}_{6}$ further undergoes a second magnetic transition from a ferrimagnet with $k=0$ to an antiferromagnetic state with $k=$ $(\frac{1}{2},$ $\frac{1}{2}, 0)$ below ${T}_{N}=15\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. A partial persistence of the $k=0$ type order leads, however, to a coexistence of both magnetic phases below ${T}_{N}$ not detected previously. The coexistence points to the energies of the magnetic ground states being very similar. Ordered magnetic moments of ${\mathrm{Ir}}^{4+}$ amounting at 1.5 K to $\ensuremath{\sim}0.6\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}$ in ${\mathrm{Pr}}_{2}{\mathrm{NiIrO}}_{6}$ and $0.4\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}$ in ${\mathrm{Nd}}_{2}{\mathrm{NiIrO}}_{6}$ are clearly detected and are compared with the expected value for the ${J}_{\mathrm{eff}}=$ $\frac{1}{2}$ model.