Properties of REAlB4 and Lu2AlB6 crystals grown from RE–Al–B (RE = Tm, Yb, Lu) melts

Abstract Crystals of TmAlB 4 , YbAlB 4 , LuAlB 4 and Lu 2 AlB 6 were grown using RE 2 O 3 (RE = Tm, Yb, Lu) and crystalline boron as starting materials in a self-component aluminum solution under an argon atmosphere at 1773 K for 10 h. REAlB 4 (RE = Tm, Yb, Lu) and Lu 2 AlB 6 crystals were generally obtained in the form of prismatic shape extending in the c direction and with well-developed {0 0 1} or {1 0 0} planes. REAlB 4 and Lu 2 AlB 4 crystals have the maximum size of approximately 3.5 mm. The as-grown crystals were measured for the Vickers microhardness at room temperature and magnetic susceptibility at low temperatures (2–300 K). The values of the Vickers microhardness for REAlB 4 and Lu 2 AlB 6 in several directions on {0 0 1} and {1 0 0} planes were in the range of 14.0 ± 0.6 to 14.5 ± 1.4 and 18.9 ± 0.7 GPa, respectively. The magnetic susceptibility of REAlB 4 (RE = Yb, Lu) and Lu 2 AlB 6 increases paramagnetically as temperature is lowered. Superconductivity was not observed in any of the samples down to a temperature of 2 K. An antiferromagnetic transition was found in TmAlB 4 with Neel transition temperature of T N  = 5.5 K.