Investigation of Structure-Property Relationships of Heavy-Fermion Materials

• Main Author: Macaluso, Robin
• Other Authors: Brian Hales
• Format: Others
• Language: en
• Published: LSU 2004
• Subjects: Chemistry
• Online Access: http://etd.lsu.edu/docs/available/etd-09172004-141159/

This work focuses on how local structural features influence large effective masses, magnetism, and superconductivity that are yet to be understood in heavy-fermion materials. Three sets of structurally-related materials are discussed in light of dimensionality, layering effects, choice of transition metal, coordination, and structural distortions: LnnMIn3n+2 (Ln = La, Ce; n = 1, 2, ; M = Co, Rh, Ir), CePdGa6, and Ce2PdGa12, and CeNiSb3. The LnnMIn3n+2 (n = 1, 2, ; Ln = La, Ce; M = Rh, Ir) intergrowth homologous series presents a unique opportunity to study structure-property relationships. LnnMIn3n+2 (Ln = La, Ce; n = 1, 2; M = Co, Rh, Ir) adopt a tetragonal structure in the space group P4/mmm. Antiferromagnetism and/or unconventional superconductivity have been found in CeCoIn5, CeRhIn5, CeIrIn5, and Ce2RhIn8. Structural trends are compared with ground state properties. Single crystals of LnPdGa6 (Ln = La, Ce) and Ln2PdGa12 (Ln = La, Ce) have been synthesized in excess Ga and characterized by X-ray diffraction. LnPdGa6 (Ln = La, Ce) form in the P4/mmm space group with lattice parameters a = b ~ 4.4 Å and c ~ 7.9 Å. Ce f-moments order antiferromagnetically along the c-axis at TN = 5.5 K. Ln2PdGa12 (Ln = La, Ce) crystallize in the tetragonal P4/nbm space group, with lattice parameters of a = 6.0370(3) Å and c = 15.4910(7) Å. It orders antiferromagnetically at TN ~ 11 K, and a spin reconfiguration transition to canted antiferromagnetism occurs at 5 K. Structure-property relationships with the CePdGa_6 are discussed. CeNiSb3 has been prepared from an Sb flux or from reaction of Ce, NiSb, and Sb above 1123 K. It crystallizes in the orthorhombic space group Pbcm with lattice parameters a = 12.6340(7) Å , b = 6.2037(3) Å , and c = 18.3698(9) Å. Its structure consists of buckled square Sb nets and layers of highly distorted edge- and face-sharing NiSb6 octahedra. Located between the [Sb] and [NiSb2] are the Ce atoms, in monocapped square antiprismatic coordination. Resistivity measurements reveal a shallow minimum near 25 K that is suggestive of Kondo lattice behaviour, followed by a sharp decrease below 6 K.