Magnetic order in the frustrated Ising-like chain compound ${\mathrm{Sr}}_3\mathrm{Ni}\mathrm{Ir}{\mathrm{O}}_6$

We have studied the field and temperature dependencies of the magnetization of single crystals of ${\mathrm{Sr}}_3\mathrm{Ni}\mathrm{Ir}{\mathrm{O}}_6$. These measurements evidence the presence of an easy axis of anisotropy and two anomalies in the magnetic susceptibility. Neutron powder diffraction realized on a polycrystalline sample reveals the emergence of magnetic reflections below 75 $\mathrm{K}$ with magnetic propagation vector k $\sim$ (0, 0, 1), undetected in previous neutron studies [T. N. Nguyen and H.-C. zur Loye, J. Solid State Chem. 117, 300 (1995)]. The nature of the magnetic ground state, and the presence of two anomalies common to this family of material, are discussed on the basis of the results obtained by neutron diffraction, magnetization measurements, and symmetry arguments.

Figure 1

Structure of ${\mathrm{Sr}}_3{\mathrm{NiIrO}}_6$ shown projected on the ($\mathbf{ab}$) plane (top) and in a perspective view (bottom). ${\mathrm{Ir}}^{4+}$ atoms are represented in orange, ${\mathrm{Ni}}^{2+}$ in blue, ${\mathrm{Sr}}^{2+}$ in green, and ${\mathrm{O}}^{2-}$ in red. The ${\mathrm{IrO}}_6$ octahedra and ${\mathrm{NiO}}_6$ trigonal prisms are represented in orange and blue, respectively. The conventional hexagonal unit cell is shown with dotted blue lines.

Figure 2

Temperature dependence of the magnetic susceptibility measured after a ZFC (filled symbol) and a FC in 0.01 $\mathrm{T}$ (empty symbol) with the magnetic field applied parallel and perpendicular to the c axis. Inset: picture of a ${\mathrm{Sr}}_3{\mathrm{NiIrO}}_6$ crystal.

Figure 3

Field dependence of the magnetization of ${\mathrm{Sr}}_3{\mathrm{NiIrO}}_6$ measured at 5 (in cyan), 15 (in dark blue), 50 (in red), and 150 (in purple) $\mathrm{K}$.

Figure 4

Magnetization hysteresis curves measured at 5, 15, and 50 $\mathrm{K}$ with the magnetic field applied parallel to c. Inset: zoom of the hysteresis curves showing the evolution of the hysteresis opening with the temperature in zero field.

Figure 5

Neutron powder diffraction of ${\mathrm{Sr}}_3{\mathrm{NiIrO}}_6$ recorded at 2 $\mathrm{K}$. The observed and calculated intensities are shown as well as the difference. Inset: zoom of the neutron powder diffraction at 2 and 100 $\mathrm{K}$ showing the onset of magnetic Bragg peaks.

Figure 6

Temperature dependence of the magnetic moments of Ni and Ir in absolute value from the refinement of the diffractograms. The plain lines are guides for the eyes.

Figure 7

Possible magnetic structures of ${\mathrm{Sr}}_3{\mathrm{NiIrO}}_6$ stabilized at low temperature in a commensurate phase with propagation vector $\mathbf{k}=(0,0,1)$. The structures correspond to two different symmetries dictated by the value of the overall phase $\phi$ of the modulation, and displayed as perspective views (top) and as sketches projected into the ab plane (bottom). The dark blue (resp. light blue) arrows indicate the magnetic moments on the Ir (resp. Ni) sites. The dashed hexagon in each structure is a guide to the eyes to highlight the transformation properties of the magnetic state under inversion symmetry (see text for details). (Left) Structure of symmetry $P\overline{3}{c}^{\prime }1$ corresponding to $\phi =0$. (Right) Structure of symmetry $P{\overline{3}}^{\prime }{c}^{\prime }1$ corresponding to $\phi =\frac{\pi }{6}$.