  The present work is concerned with the propagation of
electro-magneto-thermoelastic plane waves of assigned frequency in a
homogeneous isotropic and finitely conducting elastic medium permeated by a
primary uniform external magnetic field. We formulate our problem under the
theory of Green and Naghdi of type-III (GN-III) to account for the interactions
between the elastic, thermal as well as magnetic fields. A general dispersion
relation for coupled waves is deduced to ascertain the nature of waves
propagating through the medium. Perturbation technique has been employed to
obtain the solution of dispersion relation for small thermo-elastic coupling
parameter and identify three different types of waves. We specially analyze the
nature of important wave components like, phase velocity, specific loss and
penetration depth of all three modes of waves. We attempt to compute these wave
components numerically to observe their variations with frequency. The effect
of presence of magnetic field is analyzed. Comparative results under theories
of type GN-I, II and III have been presented numerically in which we have found
that the coupled thermoelastic waves are un-attenuated and nondispersive in
case of Green-Naghdi-II model which is completely in contrast with the theories
of type-I and type-III. Furthermore, the thermal mode wave is observed to
propagate with finite phase velocity in case of GN-II model, whereas the phase
velocity of thermal mode wave is found to be an increasing function of
frequency in other two cases. We achieve significant variations among the
results predicted by all three theories.
