  Raman spectroscopy is a very powerful probe to study the nature of
quasi-particle excitations in condensed matter physics. The work presented in
this thesis is focused on two different families of novel materials, namely the
iron-based superconductors (FeBS), multiferroic oxides and double perovskite.
Although the properties of these two systems are quite different, some
comparison can still be drawn between them. For instance, in both of these
systems magnetism plays a crucial role and intricate coupling between phononic,
magnetic and orbital degrees of freedom is crucial to understand their
underlying physics responsible for their various exotic physical properties.
Understanding the microscopic origin of quasi-particle excitations, such as
phonons, magnons, orbitons, plasmons etc., and coupling between them in these
complex materials, has been an intense field of research because it is believed
that these excitations hold the key for explaining their rich physics. The
systems studied in the thesis include (A) FeBS - (i) FeSe0.82 (ii)
Ce1-zYzFeAsO1-xFx (z = 0, 0.4; x = 0.1, 0.2) (iii) Ca4Al2O5.7Fe2As2 (iv)
Ca(Fe1-xCox)2As2 (x = 0.03, 0.05). (B) Multiferroic oxides - (i) AlFeO3 (ii)
TbMnO3 and double perovskite (iii) La2NiMnO6.
