Electronic structure, local magnetism, and spin-orbit effects of Ir(IV)-, Ir(V)-, and Ir(VI)-based compounds

Element- and orbital-selective x-ray absorption and magnetic circular dichroism measurements are carried out to probe the electronic structure and magnetism of Ir $5d$ electronic states in double perovskite ${\mathrm{Sr}}_2{M\text{IrO}}_6$ ($M=\mathrm{Mg}$, Ca, Sc, Ti, Ni, Fe, Zn, In) and ${\mathrm{La}}_2{\mathrm{NiIrO}}_6$ compounds. All the studied systems present a significant influence of spin-orbit interactions in the electronic ground state. In addition, we find that the Ir $5d$ local magnetic moment shows different character depending on the oxidation state despite the net magnetization being similar for all the compounds. Ir carries an orbital contribution comparable to the spin contribution for ${\mathrm{Ir}}^{4+} \left(5d^5\right)$ and ${\mathrm{Ir}}^{5+} \left(5d^4\right)$ oxides, whereas the orbital contribution is quenched for ${\mathrm{Ir}}^{6+} \left(5d^3\right)$ samples. Incorporation of a magnetic $3d$ atom allows getting insight into the magnetic coupling between $5d$ and $3d$ transition metals. Together with previous susceptibility and neutron diffraction measurements, the results indicate that Ir carries a significant local magnetic moment even in samples without a $3d$ metal. The size of the (small) net magnetization of these compounds is a result of predominant antiferromagnetic interactions between local moments coupled with structural details of each perovskite structure.

Figure 1

Observed (red symbol) calculated (black solid line) and difference (blue solid line) XRD Rietveld profiles for ${\mathrm{Sr}}_{2}M{\mathrm{IrO}}_6$ ($M=$ Ca, Mg, Zn, Ni) at room temperature. Bragg reflections are marked with green bars.

Figure 2

Observed (red symbol) calculated (black solid line) and difference (blue solid line) XRD Rietveld profiles for ${\mathrm{Sr}}_{2}M{\mathrm{IrO}}_6$ ($M=$ Sc, In, Fe, Ti) and ${\mathrm{La}}_2{\mathrm{NiIrO}}_6$ at room temperature. Bragg reflections are marked with green bars.

Figure 3

Magnetization vs applied field curves recorded at 5 K for compounds with nonmagnetic (top) and magnetic (bottom) $M$ atom.

Figure 4

Reciprocal susceptibility vs temperature. The inset shows the thermal dependence of the field-cooled and zero-field-cooled dc magnetic susceptibility measured under 0.1 T.

Figure 5

Ir $L_{3,2}$-edge XANES spectra recorded for a series of Ir-based oxides at $T=6$ K. The spectra have been vertically shifted for the sake of clarity.

Figure 6

Detail of the XAS white line recorded at the Ir $L_3$ edge for a series of Ir-based oxides at $T=6$ K. The inset shows the second derivative of four representative samples: Ti $\left({\mathrm{Ir}}^{4+}\right)$, Fe $\left({\mathrm{Ir}}^{5+}\right)$, Zn $\left({\mathrm{Ir}}^{6+}\right)$, and Ca $\left({\mathrm{Ir}}^{6+}\right)$.

Figure 7

Detail of the XAS white line recorded at the Ir $L_2$ edge for a series of Ir-based oxides at $T=6$ K. The inset shows the second derivative of four representative samples: Ti $\left({\mathrm{Ir}}^{4+}\right)$, Fe $\left({\mathrm{Ir}}^{5+}\right)$, Zn $\left({\mathrm{Ir}}^{6+}\right)$, and Ca $\left({\mathrm{Ir}}^{6+}\right)$.

Figure 8

(a) Ir $L_{3,2}$-edge XMCD spectra of the ${\mathrm{Ir}}^{4+}$ oxides recorded at $T=6$ K and $H=3.5$ T. (b) Ir $L_{3,2}$-edge XMCD spectra of the ${\mathrm{Ir}}^{5+}$ oxides recorded at $T=6$ K and $H=3.5$ T. (c) Ir $L_{3,2}$-edge XMCD spectra of the ${\mathrm{Ir}}^{6+}$ oxides recorded at $T=6$ K and $H=3.5$ T.

Figure 9

(a) Ir $L_{3,2}$-edge XMCD spectra of the ${\mathrm{Ir}}^{4+}$ oxides recorded at $T=6$ K and $H=3.5$ T. (b) Ir $L_{3,2}$-edge XMCD spectra of the ${\mathrm{Ir}}^{5+}$ oxides recorded at $T=6$ K and $H=3.5$ T. (c) Ir $L_{3,2}$-edge XMCD spectra of the ${\mathrm{Ir}}^{6+}$ oxides recorded at $T=6$ K and $H=3.5$ T.