Heavy fermion behavior in selected cerium-based compounds: Magnetism and superconductivity

CeRhIn₅ is a member of the recently discovered series of heavy fermion superconductors CeMIn₅ (M = Co, Rh, Ir). Initial investigations showed that CeRhIn₅ undergoes an antiferromagnetic transition at 3.8 K, but that application of pressure induces a superconducting state with the unusually high T_c of 2.1 K. With the discovery that the other members of the CeMIn₅ family were ambient pressure superconductors it became apparent that this series offered an exceptional opportunity to explore systemically the unconventional magnetic and superconducting heavy fermion ground states.; The objective of this dissertation is to explore in further detail the nature and relation of the heavy fermion magnetic and superconducting ground states in CeMIn₅ with particular emphasis on the properties of antiferromagnetic CeRhIn₅. Information about these systems will be extracted using two techniques: (1) measurements of the electrical resistivity of single crystals in applied magnetic fields to 18 T; and (2) measurements of inelastic neutron scattering response of powdered single crystals.; Magnetotransport studies reveal a high temperature regime characteristic of single impurity Kondo interactions and a low temperature regime characteristic of a Kondo lattice. Moreover, the anisotropic behavior of the resistivity of CeRhIn₅ as well as experimental and theoretical investigations of other workers indicate that crystalline electric fields strongly influence the properties of the CeMIn₅ family. To further elucidate the role of crystalline electric field effects in the CeMIn₅ series we have determined the energy level splittings and wave functions of CeRhIn₅ with inelastic neutron scattering. Using these results, along with estimations of the contribution due to the Kondo effect and magnetic interactions, reasonable fits are obtained to the measured magnetic susceptibility and specific heat. Moreover, we show that our proposal of the crystal field level splitting in CeRhIn₅ can account for the magnitude of the ordered moment observed by neutron diffraction, while those of previous work cannot. Taken together these studies indicate that any detailed understanding of the properties of these materials must account for interactions due to the Kondo effect and magnetic interactions, as well as crystalline electric field effects.