Thermal conductivity of layered borides: The effect of building defects on the thermal conductivity of TmAlB₄ and the anisotropic thermal conductivity of AlB₂

Rare earth metal borides have attracted great interest due to their unusual properties, such as superconductivity and f-electron magnetism. A recent discovery attributes the tunability of magnetism in rare earth aluminoborides to the effect of so-called "building defects." In this paper, we report data for the effect of building defects on the thermal conductivities of α-TmAlB₄ single crystals. Building defects reduce the thermal conductivity of α-TmAlB₄ by ≈30%. At room temperature, the thermal conductivity of AlB₂ is nearly a factor of 5 higher than that of α-TmAlB₄. AlB₂ single crystals are thermally anisotropic with the c-axis thermal conductivity nearly twice the thermal conductivity of the a-b plane. Temperature dependence of the thermal conductivity near and above room temperature reveals that both electrons and phonons contribute substantially to thermal transport in AlB₂ with electrons being the dominant heat carriers.