Low-temperature properties of single-crystal CrB${}_2$

Abstract

We report the low-temperature properties of ${}^{11}$B-enriched single-crystal CrB${}_2$ as prepared from high-purity Cr and B powder by a solid-state reaction and optical float zoning. The electrical resistivity, ${\rho }_{\mathrm{xx}}$, Hall effect, ${\rho }_{\mathrm{xy}}$, and specific heat, $C$, are characteristic of an exchange-enhanced Fermi liquid ground state, which develops a slightly anisotropic spin gap $\Delta \approx 220\mathrm{K}$ below $T_{\mathrm{N}}=88\mathrm{K}$. This observation is corroborated by the absence of a Curie dependence in the magnetization for $T\to 0$ reported in the literature. Comparison of $C$ with $d{\rho }_{\mathrm{xx}}/dT$, where we infer lattice contributions from measurements of VB${}_2$, reveals strong antiferromagnetic spin fluctuations with a characteristic spin fluctuation temperature $T_{\mathrm{sf}}\approx 257\mathrm{K}$ in the paramagnetic state, followed by a pronounced second-order mean-field transition at $T_{\mathrm{N}}$, and unusual excitations around $\approx T_{\mathrm{N}}/2$. The pronounced anisotropy of ${\rho }_{\mathrm{xx}}$ above $T_{\mathrm{N}}$ is characteristic of an easy-plane anisotropy of the spin fluctuations consistent with the magnetization. The ratio of the Curie-Weiss to the N$\acute{\mathrm{e}}$el temperatures, $f=-{\Theta }_{\mathrm{CW}}/T_{\mathrm{N}}\approx 8.5$, inferred from the magnetization, implies strong geometric frustration. All physical properties are remarkably invariant under applied magnetic fields up to $14\mathrm{T}$, the highest field studied. In contrast to earlier suggestions of local-moment magnetism our study identifies CrB${}_2$ as a weak itinerant antiferromagnet par excellence with strong geometric frustration.

arXiv comment15 pages, 9 figures

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