  The magnetic structure of the intermetallic antiferromagnet Sm2IrIn8 was
determined using x-ray resonant magnetic scattering (XRMS). Below TN = 14.2,
Sm2IrIn8 has a commensurate antiferromagnetic structure with a propagation
vector (1/2,0,0). The Sm magnetic moments lie in the ab plane and are rotated
roughly 18 degrees 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 two orders of magnitude at the L2 edge. At the L3 edge
both quadrupolar and dipolar features were observed in the energy line shape.
The magnetic structure and properties of Sm2IrIn8 are found to be consistent
with the general trend already seen for the Nd-, Tb- and the Ce-based compounds
from the RmMnIn3m+2n family (R = rare earth; M=Rh or Ir, m = 1, 2; n = 0, 1),
where the crystalline electrical field (CEF) effects determine the direction of
magnetic moments and the TN evolution in the series. The measured Neel
temperature for Sm2IrIn8 is slightly suppressed when compared to the TN of the
parent cubic compound SmIn3.
