Magnetic structure of ${\mathrm{Sm}}_2\mathrm{Ir}{\mathrm{In}}_8$ determined by x-ray resonant magnetic scattering

The magnetic structure of the intermetallic antiferromagnet ${\mathrm{Sm}}_2\mathrm{Ir}{\mathrm{In}}_8$ was determined using x-ray resonant magnetic scattering. Below $T_N=14.2\mathrm{K}$, ${\mathrm{Sm}}_2\mathrm{Ir}{\mathrm{In}}_8$ has a commensurate antiferromagnetic structure with a propagation vector $\vec{\eta }=(1∕2,0,0)$. The Sm magnetic moments lie in the $ab$ plane and are rotated roughly 18° away from the $a$ axis. The magnetic structure of this compound was obtained by measuring the strong dipolar resonant peak whose enhancement was of over 2 orders of magnitude at the $L_2$ edge. At the $L_3$ edge, both quadrupolar and dipolar features were observed in the energy line shape. The magnetic structure and properties of ${\mathrm{Sm}}_2\mathrm{Ir}{\mathrm{In}}_8$ are found to be consistent with the general trend already seen for the Nd-, Tb-, and the Ce-based compounds from the $R_m{M}_n{\mathrm{In}}_{3m+2n}$ family ($R=\text{rare}$ earth; $M=\mathrm{Rh}$ or Ir; $m=1,2$; $n=0,1$), where the crystalline electrical field effects determine the direction of magnetic moments and the $T_N$ evolution in the series. The measured Néel temperature for ${\mathrm{Sm}}_2\mathrm{Ir}{\mathrm{In}}_8$ is slightly suppressed when compared to the $T_N$ of the parent cubic compound $\mathrm{Sm}{\mathrm{In}}_3$.

Figure 1

Temperature dependence of the magnetization of ${\mathrm{Sm}}_2\mathrm{Ir}{\mathrm{In}}_8$ measured with transverse $\left(\theta \right)$ scans at the $(0,\frac{1}{2},9)$ peak.

Figure 2

Energy scan of the $(\frac{1}{2},0,9)$ magnetic peak at $T=5.9\mathrm{K}$ for $\sigma \text{−}{\pi }^{\prime }$ (closed circles) and $\sigma \text{−}{\sigma }^{\prime }$ (open circles) polarization channels at the $L_2$ (top) and $L_3$ (bottom) absorption edges. The data have been corrected for absorption, $\mu \left(E\right)$, using the measured fluorescence yield. Arrows indicate the scales for the fluorescence yield (right) and the observed data (left). The vertical dashed lines show the energy positions of the absorption edges for $\mathrm{Sm}{L}_2$ edge ($E=7.312\mathrm{keV}$) and $\mathrm{Sm}{L}_3$ edge ($E=6.716\mathrm{keV}$).

Figure 3

Analysis of the possible magnetic moment directions for ${\mathrm{Sm}}_2\mathrm{Ir}{\mathrm{In}}_8$ at the $L_2$ resonance. $\mathbf{Q}$ dependence of the integrated intensities of (a) six satellite peaks signal in the $\pi \text{−}{\sigma }^{\prime }$ channel with the moments along $\widehat{a}$ and $\widehat{c}$ and (b) in the $\pi \text{−}{\pi }^{\prime }$ with moments parallel to $\widehat{b}$.

Figure 4

Normalized relatively integrated intensities of the $(\frac{1}{2},0,9)$ magnetic peak at $T=6.5\mathrm{K}$ (open circles) as a function of the azimuth angle. The other curves represent the variation expected for the magnetic moments along the $\widehat{a}$ (dotted line), $\widehat{b}$ (dashed line), and 18° away from $\widehat{a}$ (solid line), directions.

Figure 5

Magnetic structure of ${\mathrm{Sm}}_2\mathrm{Ir}{\mathrm{In}}_8$ below $T_N=14.2\mathrm{K}$ (left) and a Sm-In plane top view (right) showing the arrangement of Sm moments within the $\mathrm{Sm}{\mathrm{In}}_3$ blocks.

Figure 6

Field dependence of the integrated intensities of the $(\frac{1}{2},0,9)$ and $(0,\frac{1}{2},9)$ magnetic peaks taken with transverse $\left(\theta \right)$ scans around each reciprocal space lattice points (top axis for open symbols and bottom axis for solid symbols). (a) For $H=0$ applied field at $T=6\mathrm{K}$ and (b) field cooled from $16\text{to}6\mathrm{K}$ at $H=10\mathrm{T}$.