Single-Crystal Growth of a Cubic Laves-Phase Ferromagnet HoAl2 by a Laser Floating-Zone Method

The successful growth of single crystals of a cubic Laves-phase material HoAl2 with the space group Fd-3m is reported. The crystals were grown by a floating-zone method with five laser di-odes as a heat source. Al-rich feed rods were prepared for compensation of heavy evaporation during the growth. The nominal ratio for the feed rods was optimized as Ho : Al = 1 : 2.5. Single crystals of HoAl2 with a length of 50 mm were firstly grown in this technique. Obtaining the large-size crystal by the floating-zone method enabled us to systematically explore the physical properties using the same batch crystal. The crystal possessed a second-ordered ferromagnetic transition at 29 K and a first-ordered spin-reorientation transition at 20 K. The bulk physical properties such as specific heat, magnetic susceptibility, isothermal magnetization, and thermal expansion measurements were measured. Also, a magnetocaloric effect was evaluated by the magnetic entropy change. We systematically demonstrate that anisotropic physical properties along the principal axes ([100], [110], and [111]) emerged below the magnetically ordered states, in contrast to the isotropic behavior in the paramagnetic state.