Physical Properties of Single Crystalline R Mg 2 Cu 9 ( R = Y , Ce − Nd , Gd − Dy , Yb ) and the Search for In - Plane Magnetic Anisotropy in Hexagonal Systems

Single crystals of RMg 2 Cu 9 (R = Y, Ce-Nd, Gd-Dy, Yb) were grown using a high-temperature solution growth technique and were characterized by measurements of room-temperature x-ray diffraction, temperature-dependent specific heat, and temperature-and field-dependent resistivity and anisotropic magnetization. YMg 2 Cu 9 is a non-local-moment-bearing metal with an electronic specific heat coefficient, γ ∼ 15 mJ/mol K 2. Yb is divalent and basically non-moment-bearing in YbMg 2 Cu 9. Ce is trivalent in CeMg 2 Cu 9 with two magnetic transitions being observed at 2.1 K and 1.5 K. PrMg 2 Cu 9 does not exhibit any magnetic phase transition down to 0.5 K. The other members being studied (R = Nd, Gd-Dy) all exhibit antiferromagnetic transitions at low temperatures ranging from 3.2 K for NdMg 2 Cu 9 to 11.9 K for TbMg 2 Cu 9. Whereas GdMg 2 Cu 9 is isotropic in its paramagnetic state due to zero angular momentum (L = 0), all the other local-moment-bearing members manifest an anisotropic, planar magnetization in their paramagnetic states. To further study this planar anisotropy, detailed angular-dependent magnetization was carried out on magnetically diluted (Y 0.99 Tb 0.01)Mg 2 Cu 9 and (Y 0.99 Dy 0.01)Mg 2 Cu 9. Despite the strong, planar magnetization anisotropy, the in-plane magnetic anisotropy is weak and field-dependent. A set of crystal electric field parameters are proposed to explain the observed magnetic anisotropy.