Unusual magnetic ordering in the intermetallic compound UNi₄B

Abstract

We have investigated the low-temperature specific heat, susceptibility and resistivity of a new uranium transition-metal boride UNi₄B. This compound crystallizes in the hexagonal CeCo₄B structure, with lattice parameters a=4.950 Å and c = 6.962 Å. In contrast with other uranium borides, the compound orders antiferromagnetically at T _N = 20·0 ± 0·1K. Its electronic specific heat coefficient γ is 244·8 mJ K⁻² mol⁻¹ for T > T _N, which is near the heavy-fermion regime. Below T _N, all properties behave anomalously. The resistivity falls off only very slowly, while both the electronic specific heat and the susceptibility exhibit minima and increase as T → 0.