Thermal conductivity of layered borides: The effect of building defects on the thermal conductivity of TmAlB4and 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 alumino borides to the effect of so-called ldquobuilding defects.rdquo In this paper, we report data for the effect of building defects on the thermal conductivities of alpha-TmAlB 4 single crystals. Building defects reduce the thermal conductivity of alpha-TmAlB 4 by ap30%. At room temperature, the thermal conductivity of AlB 2 is nearly a factor of 5 higher than that of alpha-TmAlB 4. AlB 2 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 AlB 2 with electrons being the dominant heat carriers