NMR determination of 2D electron spin polarization at ν = 1/2

Using a “standard” NMR spin-echo technique we determined the spin polarization P of two-dimensional electrons, confined to GaAs quantum wells, from the hyperfine shift of Ga nuclei located in the wells. Concentrating on the temperature (0.05 ≲ T ≲ 10K) and magnetic field (7 ≲ B ≲ 17T) dependencies of P at Landau level filling factor ν = 1/2, we find that the results are described well by a simple model of noninteracting composite fermions, although some inconsistencies remain when the two-dimensional electron system is tilted in the magnetic field.