The effect of magnetic field dependent (MFD) viscosity on the thermal convection in a ferrofluid layer saturating a sparsely distributed porous medium has been investigated by using the Darcy-Brinkman model in the simultaneous presence of a uniform vertical magnetic field and a uniform vertical rotation. A correction is applied to the study of Vaidyanathan et al.  which is very important in order to predict the correct behavior of MFD viscosity. A linear stability analysis has been carried out for stationary modes and oscillatory modes separately. 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 M1. Numerical results are obtained and are illustrated graphically. It is shown that magnetic field dependent viscosity has a destabilizing effect on the system for the case of stationary mode and a stabilizing effect for the case of oscillatory mode, whereas magnetization has a destabilizing effect.
 Odenbach S. (2002a): Magnetoviscous Effects in Ferrofluids. – New York: Springer.
 Elmore W.C. (1938): The magnetization of ferromagnetic colloids. – Phys. Rev., vol.54, pp.1092-1095.
 Finlayson B.A. (1970): Convective instability of ferromagnetic fluids. – J. Fluid Mech., vol.40, pp.753–767.
 Shliomis M.I. (1972): Effective viscosity of magnetic suspensions. – Sov. Phys. JETP, vol.34, No.6, pp.1291-1294.
 Odenbach S. (2002b): Ferrofluids: Magnetically Controllable Fluids and Their Applications. – New York: Springer.
 Suslov S.A. (2008): Thermomagnetic convection in a vertical layer of ferromagnetic fluid. - Phys. Fluids, vol.20, No.8, pp.084101.
 Rahman H. and Suslov S.A. (2016): Magneto-gravitational convection in a vertical layer of ferrofluid in a uniform oblique magnetic field. – J. Fluid Mech., vol.795, pp.847-875.
 Sekar R. and Murugan D. (2018): Linear stability effect of densely distributed porous medium and Coriolis force on Soret driven Ferrothermohaline convection. – Int. J. Appl. Mech. Engng., vol.23, No.4, pp.911-928.
 Vaidyanathan G., Sekar R., Vasanthakumari R. and Ramanathan A. (2002): The effect of magnetic field dependent viscosity on ferroconvection in a rotating sparsely distributed porous medium. – J. Magn. Magn. Mater., vol.250, pp.65-76.
 Ramanathan A. and Suresh G. (2004): Effect of magnetic field dependent viscosity and anisotropy of porous medium on ferroconvection. – Int. J. Engng. Sc., vol.42, pp.411-425.
 Prakash J. and Gupta S. (2013): On arresting the complex growth rates in ferromagnetic convection with magnetic field dependent viscosity in a rotating ferrofluid layer. – J. Magn. Magn. Mater., vol.345, pp.201-207.
 Prakash J. (2014): On the characterization of non-oscillatory motions in ferromagnetic convection with magnetic field dependent viscosity in a rotating porous medium. – J. Egypt. Math. Soc., vol.22, pp.286-291.
 Prakash J. and Bala R. (2016): On estimating the complex growth rates in ferromagnetic convection with magnetic field dependent viscosity in a rotating sparsely distributed porous medium. – J. Appl. Mech. Tech. Phy., vol.57, No.4, pp.623-636.
 Prakash J., Kumar R. and Kumari K. (2017): Thermal convection in a ferromagnetic fluid layer with magnetic field dependent viscosity. a correction applied. – Studia Geotech. et Mech., vol.39, No.3, pp.39-46.
 Prakash J., Kumar P., Kumari K. and Manan S. (2018a): Ferromagnetic convection in a densely packed porous medium with magnetic field dependent viscosity – revisited. – Z. Naturforsch., vol.73, No.3, pp.181-189.
 Prakash J., Manan S. and Kumar P. (2018b): Ferromagnetic convection in a sparsely distributed porous medium with magnetic field dependent viscosity. revisited. - J. Porous Media, vol.21, No.8, pp.749-762.
 Chandrasekhar S. (1981): Hydrodynamic and Hydromagnetic Stability. – New York: Dover Publications, Inc.
 Vaidyanathan G., Sekar R. and Balasubramanian R. (1991): Ferroconvective instability of fluids saturating a porous medium. –Int. J. Engng. Sc., vol.29, No.10, pp.1259-1267.
 Shivakumara I.S., Jinho L., Nanjundappa C.E. and Ravisha M. (2011): Ferromagnetic convection in a rotating ferrofluid saturated porous layer.–Transp. Porous Med., vol.87, No.1, pp.251–273.
 Venkatasubramanian S. and Kaloni P.N. (1994): Effects of rotation on the thermoconvective instability of a horizontal layer of ferrofluids. –Int. J. Engng. Sc., vol.32, No.2, pp.237-256.
 Walker K. and Homsy G.M. (1977): A note on convective instabilities in boussinesq fluids and porous media. – J. Heat Transfer, vol.99, No.2, pp.338-339.
 Vaidyanathan G., Sekar R. and Ramanathan A. (1997): Ferrothermohaline convection. –J. Magn. Magn. Mater., vol.176, pp.321-330.