Exploring the magnetostructural phases of the layered ruthenates with Raman scattering

This chapter reviews the methods used and results obtained in inelastic light (Raman) scattering studies of the layered ruthenates; the particular focus of this review is on the temperature-, magnetic-field, and pressure-dependent magnetic and orbitally polarized phases of these materials. The results described here show clearly that structural changes associated with the RuO₆ octahedra—induced variously by temperature, atomic substitution, magnetic field, and pressure—play a definitive role in many of the exotic properties and phases observed in the layered ruthenates. In Raman scattering, this is evidenced, in particular, by anomalous behavior of the B_1gsymmetry RuO₆ octahedral phonon mode in all the ruthenate materials studied. After a brief description of the theory of Raman scattering in solids to provide backround information for the reader (Section 4.2), the low temperature, high pressure, and high magnetic field Raman scattering methods used in these studies are discussed (Section 4.3). Finally, temperature-, magnetic field-, and pressure-dependent Raman scattering results are discussed for single layered Ca_2-xSr_xRuO₄ (Section 4.4), bilayered Ca₃Ru₂O₇ (Section 4.5), and triple-layered Sr₄Ru₃O₁₀ (Section 4.6)