Open Access Version

Abstract:
In this thesis three new, three-dimensional (3D) magnetic cubic systems, with spin lattices that provide ideal conditions for geometrical frustration and effective spin- 1/2 moments are investigated via magnetization, heat capacity, neutron scattering and other techniques. Nd2Hf2O7 and Pr2Hf2O7 are two pyrochlore compounds with the light rare earth magnetic ions to be approximated at low temperatures as spin effective-1/2. The strong spin orbit coupling accompanied with the unusual CEF result in the energetic preference of the spins to lie along the local [1 1 1] direction. Nd2Hf2O7 shows an AFM transition and the spins order in an ‘all-in all-out’ pattern. Simultaneously the gapped magnetic excitations which are highlighted by a set of pinch point and halfmoon features suggest, by fitting with a proper XYZ model, a dominant transverse FM interaction that explains the strong quantum fluctuations and an AFM longitudinal interaction that orders the system. Finally, data just above the transition temperature imply a closing of the gap and the possibility of the formation of an exotic U(1)-quantum spin liquid state. Pr2Hf2O7 on the other hand does not show any signs of long range order down to the lowest temperatures. A static pinch point pattern is revealed accompanied by broad diffusive excitations. These excitations remain dispersive even after applying magnetic fields up to 5 T. The data suggest that the ground state shows properties of a quantum spin liquid candidate, nevertheless we do not exclude the possibility that structural disorder drives the ground state away from the spin liquid regime, in the paramagnetic state. BaCuTe2O6 consists of a complex 3D network of Cu2+ ions. Our data indicate the appearance of one dimensional spin-1/2 Heisenberg AFM spin-chain correlations that precede the system’s order at lower temperatures, due to inter-chain couplings. The data suggest the appearance of two inter-chain couplings, one of which creates the frustrated 3D spin-network of corner sharing triangles, which is known in literature as hyper-Kagome, forcing the system into an ordered state. Nevertheless only a theoretical study could reveal the true nature of interactions.