Ferromagnetic Convection in a Densely Packed Porous Medium with Magnetic-Field-Dependent Viscosity - Revisited

The effect of magnetic-field-dependent (MFD) viscosity on the thermal convection in a ferromagnetic fluid in the presence of a uniform vertical magnetic field is investigated for a fluid layer saturating a densely packed porous medium using the Darcy model. A correction is applied to the model by Sunil et al. [Z. Naturforsch. 59, 397 (2004)], which is very important to predict the correct behaviour of MFD viscosity. A linear stability analysis is carried out for stationary modes. The critical wave number and critical Rayleigh number for the onset of instability, for the case of free boundaries, are determined numerically for sufficiently large values of the magnetic parameter M-1. Numerical results are obtained and illustrated graphically. It is shown that MFD viscosity has stabilizing effect on the system, whereas medium permeability has a destabilizing effect.