Low-temperature properties of single-crystal CrB2

We report the low-temperature properties of B-11-enriched single-crystal CrB2 as prepared from high-purity Cr and B powder by a solid-state reaction and optical float zoning. The electrical resistivity, rho(xx), Hall effect, rho(xy), and specific heat, C, are characteristic of an exchange-enhanced Fermi liquid ground state, which develops a slightly anisotropic spin gap Delta approximate to 220 K below T-N = 88 K. This observation is corroborated by the absence of a Curie dependence in the magnetization for T -> 0 reported in the literature. Comparison of C with d(rho xx)/dT, where we infer lattice contributions from measurements of VB2, reveals strong antiferromagnetic spin fluctuations with a characteristic spin fluctuation temperature T-sf approximate to 257 K in the paramagnetic state, followed by a pronounced second-order mean-field transition at T-N, and unusual excitations around approximate to T-N/2. The pronounced anisotropy of rho(xx) above TN is characteristic of an easy-plane anisotropy of the spin fluctuations consistent with the magnetization. The ratio of the Curie-Weiss to the Neel temperatures, f = -Theta(CW)/T-N approximate to 8.5, inferred from the magnetization, implies strong geometric frustration. All physical properties are remarkably invariant under applied magnetic fields up to 14 T, the highest field studied. In contrast to earlier suggestions of local-moment magnetism our study identifies CrB2 as a weak itinerant antiferromagnet par excellence with strong geometric frustration.