Over the last three decades or so, magnetic frustration, as a result of competition
between interactions that cannot be satisfied simultaneously, is a central theme in
contemporary condensed matter physics as it yields exotic quantum ground states such as spin-glass, spin-liquid, spin-ice, order-by-disorder, cooperative paramagnetism, and the intriguing monopole phenomenon. Compounds containing lanthanide ions have been attracting lots of interests because the fact that they often exhibit anomalous magnetic properties that can be traced to magnetic frustration. Among them, much attention has been paid to the magnetic materials with strong geometrical frustration, such as stacked triangular lattices, two- and three-dimensional (3D) Kagomé lattices, and 3D networks of corner-sharing (pyrochlores and spinels) or edge-sharing tetrahedra. Many of these systems are still not well understood at present, and these frustrated systems provide an excellent testing ground for approximations and theories.
Recently, a new family of geometrically frustrated magnetic materials SrRE2O4 (RE = rare earth) adopts an orthorhombic (Pnam) structure in which the magnetic lanthanide sublattice consists completely of triangle-chains of edge-shared lanthanide triangles in a honeycomb-like arrangement. The particular geometry combines exchange interactions with crystal field anisotropy dependent on rare-earth ions to produce some novel magnetic properties with both classical and quantum spin-liquid phases. In addition, the highly degenerated ground state could be lifted by small perturbation.
In this dissertation, the single crystals of SrRE2O4 (RE = rare earth) have been
synthesized successfully by the laser diode floating zone (LDFZ) method. The
structure has been studied by X-ray powder diffraction (XRPD), the stoichiometry has been confirmed with EDS, and the unit cell parameters and atomic positions have been determined by neutron powder diffraction (NPD). We also utilized inelastic neutron scattering (INS) technique to investigate the magnetic excitations of SrTb2O4.
Magnetic measurements under ambient pressure as well as micro-pressure have been performed on the series of the Tb, Dy, and Ho members in terms of susceptibility versus temperature. Furthermore, we also carried out the electric polarization measurements on the single crystals of SrRE2O4 (RE = Tb, Dy, and Ho), and some intriguing phenomena have been discovered.