Heavy fermion behavior in the new antiferromagnetic compound UIr ₄Al₁₅

We report the synthesis, crystal structure, and physical properties on the new compound UIr₄Al₁₅ which crystallizes with the NdRh₄Al_15.4 structure type in the tetragonal space group P4₂/nmc. From single crystal X-ray diffraction, the compound was found to have unit cell parameters a = b = 9.0239(6) and c = 15.513(2) Å. The compound has been synthesized from the flux growth method using an excess of Al metal. UIr₄Al₁₅ undergoes antiferromagnetic order at approximately 20 K which is consistent with kinklike features in both electrical resistivity and specific heat measurements. Electrical resistivity under hydrostatic pressure shows that the antiferromagnetic ordering temperature is slightly shifted to higher temperatures which is suggestive of the very little pressure dependence and the localized nature of the U 5f electrons. Electronic structure calculations indicated that the Fermi surface of UIr ₄Al₁₅ was quasi two-dimensional.