First order magnetic transition and magnetoelastic effects in [formula omitted

Abstract

We report measurements of temperature dependent heat capacity, thermal expansion and high resolution X-ray diffraction (XRD) taken on single crystals of Sm 2 IrIn 8 intermetallic compound. This compound belongs to the R m M n In 3 m + 2 n 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, Sm 2 IrIn 8 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 T N = 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 Ce 2 RhIn 8 and CeRhIn 5 . 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.