Field-Induced Orbital and Magnetic Phases in the Layered Ruthenates

Magnetic-field- and Temperature-dependent Raman scattering studies have been performed on Ca$_{3}$Ru$_{2}$O$_{7}$, which undergoes an antiferromagnetic transition at 56K and a metal-insulator transition at 48K. Although no appreciable changes in the magnon or phonon spectra are observed for fields oriented along the c-axis, a field applied in the a-b plane reveals dramatic magnetic-induced changes to both the magnon and phonon spectra. For fields aligned along the magnetic easy-axis (a-axis), a splitting in the magnon mode occurs with increasing field, as well as evidence for a metamagnetic transition above 5 T, based upon which we can deduce several magnetic parameters for this material. Furthermore, by monitoring the field-induced changes in the Ru-O phonon frequency at various temperatures, we are able to map-out various field-induced orbital and magnetic phases for fields applied along both the hard and easy axis directions. *Work supported by NSF DMR02-44502, DOE DEFG02-91ER45439, and the Sony Scholar Fund.