  We present results on resistivity ($\rho$), magnetization ($M$), thermal
conductivity ($\kappa$), magnetostriction ($\frac{\Delta L}{L(0)}$) and
specific heat ($C_{p}$) of charge-orbital ordered antiferromagnetic
Nd$_{0.8}$Na$_{0.2}$MnO$_{3}$ compound. Magnetic field-induced
antiferromagnetic/charge-orbital ordered insulating to ferromagnetic metallic
transition leads to giant magnetothermal conductivity and magnetostriction
effect. The low-temperature irreversibility behavior in $\rho$, $M$, $\kappa$
and $\frac{\Delta L}{L(0)}$ due to field cycling together with striking
similarity among the field and temperature dependence of these parameters
manifest the presence of strong and complex spin-charge-lattice coupling in
this compound. The giant magnetothermal conductivity is attributed mainly to
the suppression of phonon scattering due to the destabilization of spin
fluctuations and static/dynamic Jahn-Teller distortion by the application of
magnetic field.
