First order magnetic transition and magnetoelastic effects in Sm2IrIn8

We report measurements of temperature dependent heat capacity, thermal expansion and high resolution X-ray diffraction (XRD) taken on single crystals of Sm2IrIn8 intermetallic compound. This compound belongs to the RmMnIn3m+2n family (R=rare earth, m=1, 2, n=0, 1 and M=Rh, Ir and Co) which includes a number of heavy fermion superconductors for R=Ce. Particularly, Sm2IrIn8 is the only member of this family to present a first order magnetic phase transition (FOMT). Both thermal expansion and heat capacity data show very pronounced sharps peaks at TN=14.2 K consistent with an FOMT. The linear thermal-expansion coefficient is anisotropic and both c-axis and basal ab plane coefficients change discontinuously at 14.2 K. This change is negative for both direction in contrast to what was found for other members of family such as Ce2RhIn8 and CeRhIn5. The zero-field high resolution XRD data at 14.2 K shows no evidence for a tetragonal-to-orthorhombic structural phase transition. We discuss our results considering tetragonal crystalline field effects (CEF), quadupolar interactions, antiferromagnetic domains and magnetoelastic effects