Im. Mryglod et R. Folk, ON THE HYDRODYNAMIC THEORY OF A MAGNETIC LIQUID .2. HYDRODYNAMIC MODES IN THE HEISENBERG FLUID, Physica. A, 234(1-2), 1996, pp. 129-150
On the basis of our previous results (Physica A 220 (1995) 325) the co
llective mode spectrum of the Heisenberg ferrofluid model is studied i
n the hydrodynamic region. We start from the rigorous microscopic appr
oach taking into account all conserved quantities and calculate the ex
plicit expressions for the dispersion and damping coefficient of sound
modes. It is shown that the sound velocity of Heisenberg ferrofluid a
t constant external magnetic held is isotropic and can be expressed by
the adiabatic compressibility at constant magnetization m. We also ca
lculate the heat and spin modes which are purely diffusive. Explicit e
xpressions for the viscosity, thermal conductivity, spin diffusion and
thermomagnetic diffusion coefficients containing time correlation fun
ctions are derived. Our results are compared with previous ones obtain
ed mainly within phenomenological theories.