Single-crystal growth and investigation of intertwined magnetic and lattice frustration in triangular-lattice compounds ReCd₃P₃ (Re = La – Sm)

The rare-earth triangular lattice compounds ReCd₃P₃ (Re = La–Sm) constitute a compelling family of materials that showcase a delicate interplay between geometric frustration, magnetic correlations, and anisotropic charge transport. These compounds crystallize in the hexagonal space group P6₃/mmc, featuring well-separated triangular layers of Re³⁺ ions (spaced by more than 10 Å). Between these layers lie cadmium phosphide sheets containing unusual trigonal-planar Cd₃P units, which form a bond-frustrated honeycomb network exhibiting dynamic bond fluctuations. This architecture gives rise to a unique coexistence of magnetic frustration on the Re³⁺ sublattice and bond frustration within the Cd₃P network, intricately coupled in a single framework. The electronic structure of ReCd₃P₃ is remarkably sensitive, making its transport properties highly dependent on synthesis conditions. In this work, we report a refined salt-flux synthesis method for growing cm-scale single crystals of ReCd₃P₃ and Sr-doped derivatives. Comprehensive magnetic susceptibility, heat capacity, electrical transport, second-harmonic generation (SHG), synchrotron X-ray scattering, and inelastic neutron scattering measurements are presented, providing new insights into the intertwined lattice, charge, and spin dynamics of this geometrically frustrated system.