Competing Exchange Interactions in Lanthanide Triangular Lattice Compounds <i>Ln</i>Zn<sub>3</sub>P<sub>3</sub> (<i>Ln</i> = La–Nd, Sm, Gd)
N. Kabeya, Tomohiro Sakamoto, Katsuya Hara, Yuta Hara, Shintaro Nakamura, Kenichi Katoh, Akira Ochiai
Abstract
Stacked triangular lanthanide compounds LnZn3P3 (Ln = La–Nd, Sm, Gd) are successfully grown as single-crystalline samples. Magnetic-susceptibility and specific-heat measurements reveal that the compounds with Ce, Nd, and Gd show long-range order at 0.78, 0.63, and 4.7 K, respectively, while two successive transitions are found in SmZn3P3 at 0.34 and 0.82 K. The light lanthanide compounds LnZn3P3 (Ln = La–Pr) behave as semiconductors in terms of electrical resistivity, while heavier lanthanide compounds (Ln = Nd, Sm, Gd) show metallic conductivity. This family of compounds provides an excellent opportunity to study the effects of conduction electrons in rare-earth triangular-lattice magnets. The ordering temperatures of the metallic compounds are almost proportional to the de-Gennes factor of those trivalent lanthanide ions. In contrast, the semiconductor compound CeZn3P3 shows a much higher ordering temperature than that estimated from the de-Gennes factor. Our results indicate that even with a low density of conduction electrons, the Ruderman–Kittel–Kasuya–Yosida interaction possibly has a comparable magnitude to the superexchange interaction and shows the potential to remove geometrical frustration.