Magnetic Structure of ${\mathrm{RuSr}}_2{\mathrm{GdCu}}_2{\mathbf{O}}_8$ Determined by Resonant X-Ray Diffraction

X-ray diffraction with photon energies near the Ru $L_2$-absorption edge was used to detect resonant reflections characteristic of a $G$-type superstructure in ${\mathrm{RuSr}}_2{\mathrm{GdCu}}_2{\mathrm{O}}_8$ single crystals. A polarization analysis confirms that these reflections are due to magnetic order of Ru moments, and the azimuthal-angle dependence of the scattering amplitude reveals that the moments lie along a low-symmetry axis with substantial components parallel and perpendicular to the ${\mathrm{RuO}}_2$ layers. Complemented by susceptibility data and a symmetry analysis of the magnetic structure, these results reconcile many of the apparently contradictory findings reported in the literature.

Figure 1

Energy dependence of the scattered intensity at the reflections $(\frac{1}{2}\frac{1}{2}\frac{1}{2})$ and $(\frac{1}{2}\frac{1}{2}\frac{3}{2})$ near the Ru $L_2$-absorption edge. The energy profiles are not corrected for absorption. The inset shows a typical longitudinal reciprocal-space scan at reflection $(\frac{1}{2}\frac{1}{2}\frac{1}{2})$ taken with photon energy 2.968 keV.

Figure 2

Temperature dependence of the integrated intensity of the magnetic reflections $(\frac{1}{2}\frac{1}{2}\frac{1}{2})$ and $(\frac{1}{2}\frac{1}{2}\frac{3}{2})$. The Néel temperature of about 102 K agrees with the one found by field cooled magnetization measurements shown in the inset, which were carried out on single crystals at 100 Oe.

Figure 3

Azimuthal dependence of the integrated scattering intensity at reflection $(\frac{1}{2}\frac{1}{2}\frac{1}{2})$ at $T=43\mathrm{K}$, where $\psi =0$ is defined in such a way that $(102)$ lies in the diffraction plane. The solid line is the result of a fit to a theoretical expression for the resonant electric dipole scattering intensity, as explained in the text.