Structural and magnetic properties of LnNiGa4 (Ln = Y, Gd-Yb)*

Rare earth intermetallic compounds often display a competition between RKKY- and Kondo-type interactions as evident inmagnetic and transport properties. To understand how exchange interactions vary with rare earth elements, we have synthesized and studied a series of LnNiGa4 (Ln = Y, Gd - Tm) compounds. Single crystals of the orthorhombic LnNiGa4 with Cmcm space group symmetry have been grown. Along the crystallographic b-axis, slabs of Ni@Ga7Ln2 and non-magnetic slabs of Ga-only atoms alternate throughout the lattice. Two distinct Ga-sites have been confirmed with X-ray photoelectron spectroscopy. In addition, XPS of TmNiGa4 shows that Ni is in the metallic state. There is a transition from antiferromagnetic to ferromagnetic behavior in the series. The magnetic susceptibility and magnetization measurements reveal magnetic moments larger than expected for a free rare earth ion and is due to conduction electrons contributing to the magnetism. The changes in the Curie-Weiss temperatures are consistent with an RKKY coupling of the magnetic moments.