Thermodynamics and spin polarizations of the fractional quantum Hall states

The filling factor and temperature dependence of the electron spin polarization [S-z(T)] of a two-dimensional electron system have been studied for various values of Zeeman coupling. At T = 0, there are sharp spin transitions for all the filling fractions considered here except v = 1/3. At low T, the appearance of a peak in [S-z(T)] at v = 2/3 and v = 2/5 is interpreted as a manifestation of the reentrant behavior observed earlier. At v = 3/5, one sees a gradual trasition from one spin state to another at low T. At large T, [S-z(T)] generally decays as T-1. These can be explored in the optically pumped nuclear magnetic resonance Knight shift measurements.