  In the present work we investigate the r-mode instability windows, spindown
and spindown rates of sub- and super-Chandrasekhar magnetized white dwarfs in
presence of Landau quantization of the electron gas and magnetic braking. The
gravitational wave strain amplitudes due to r-mode instability is also
calculated. The dominant damping mechanism is taken to be the shear viscosity
arising due to scattering of the degenerate electrons from the ion liquid. We
find that the critical frequencies of Landau quantized magnetized white dwarfs
are the lowest, those of non-Landau quantized ones are higher and those of
non-magnetized ones are the highest at the same temperature. This implies that
magnetic braking and Landau quantization both enhance r-mode instability. We
have also seen that there is rapid spindown of magnetized white dwarfs due to
additional magnetic braking term but there is no considerable effect of Landau
quantization on the spindown and spindown rates for magnetic field strengths
relevant for white dwarf interiors. We find that the r-mode gravitational wave
strain amplitude for a rapidly rotating super-Chandrasekhar white dwarf at 1
kpc is $\sim 10^{-27}$, making isolated massive rapidly rotating hot magnetized
white dwarfs prime candidates for search of gravitational waves in the future.
