Structure, magnetism, and thermodynamics of the novel rare earth-based R5T4 intermetallics

After approximately 30 years of dormancy, the binary, ternary, and multicomponent intermetallic compounds of rare earth metals (R) with the group 14 elements (T) at the R5T4 stoichiometry have become a goldmine for materials science, condensed matter physics, and solid-state chemistry. In addition to providing numerous opportunities to clarify elusive structure-property relationships, the R5T4 compounds may soon be developed into practical materials by exploiting their unique sensitivity toward a variety of chemical and physical triggers. The distinctiveness of this series is in the remarkable flexibility of the chemical bonding between well-defined, self-assembled, subnanometer-thick slabs and the resultant magnetic, transport, and thermodynamic properties of the R5T4 compounds that can be controlled by varying either or both R and T, including mixed rare earth elements on the R-sites and different group 14 (and 13 or 15) elements occupying the T-sites. In addition to chemical means, the interslab interactions are tunable by temperature, pressure, and magnetic field. Presently, a substantial, yet far from complete, body of knowledge exists about the Gd compounds with T = Si and Ge. In contrast. only a little is known about the physics and chemistry of R5T4 alloys with other lanthanides, while compounds with T = Sn and Pb remain virtually unexplored.