Magnetic structure and orbital state of ${\text{Ca}}_3{\text{Ru}}_2{\text{O}}_7$ investigated by resonant x-ray diffraction

Resonant x-ray diffraction at the ${\text{L}}_2$- and ${\text{L}}_3$-absorption edges of Ru has been used to investigate the magnetic structure of ${\text{Ca}}_3{\text{Ru}}_2{\text{O}}_7$, a material with a bilayer perovskite structure that undergoes a transition from a high-temperature metallic to a low-temperature insulating phase at 48 K. In the insulating phase, magnetic Bragg reflections characteristic of $A$-type antiferromagnetic order (that is, ferromagnetic ${\text{RuO}}_2$ bilayers coupled antiferromagnetically along the $c$-axis) were identified. The azimuthal-angle dependence of the diffracted intensity implies that the magnetic moments are aligned along the $b$-axis in the ${\text{RuO}}_2$ planes. In the metallic phase, the $A$-type magnetic order persists up to the Néel temperature of 56 K, but the sublattice magnetization decreases by a factor of $\sim 1.7$ and rotates by $90°$ within the planes. Resonant signals characteristic of uniform or staggered orbital order were not found within the experimental sensitivity, probably reflecting a weak orbital polarization in the insulating state.

Figure 1

(Color online) Schematic picture of the experimental setup.

Figure 2

(Color online) Energy dependence of the diffracted intensity at the magnetic reflections (001) and (110) near the $L$-absorption edges of Ru. The energy profiles are not corrected for absorption.

Figure 3

(Color online) Azimuthal-angle dependence of the scattered intensity at the (001) and (110) reflection measured below and above $T_{MI}$. The solid lines are calculations based on the electric-dipole approximation and a magnetic moment direction along the $b$-axis below and along the $a$-axis above $T_{MI}$.

Figure 4

(Color online) Temperature dependence of the integrated intensity at the magnetic reflections (001) and (110) taken at the azimuthal position $\psi =0°$. The inset shows the temperature dependence of the scattered intensity at wave vector (110) for $\psi =0°$ and $\psi =180°$.

Figure 5

(Color online) Energy scans for ${\varphi }_A=85°$ and ${\varphi }_A=95°$ at the reflection (060) taken at two azimuthal positions $\psi =0°$ and $\psi =90°$ measured at 20 K.