Polarized neutron scattering of D2O-based magnetic fluids (depolarization)

Magnetite colloidal fluid with a carrier fluid of deuterium oxide (D2O) was prepared to eliminate the incoherent scattering by hydrogen nucleons and the depolarization of cold neutrons was measured. The magnetic fluid was cooled down to 17 K in an external magnetic field of 10 kOe. The sample exhibited a finite residual magnetization Mr, which decreases with increasing temperature from 17 K. With elevating the temperature from 17 to 300 K, the depolarization was measured in three cases in which the directions of the beam, Mr, and polarization are mutually changed. The polarized neutrons transmitting through the sample were depolarized by the magnetic moments in the colloidal particles. The polarizations as a function of the product of Mr and neutron wavelength λ at different temperatures reduce to the same functional form. The model which shows that no interactions exist among the ferrous colloidal particles succeeds partly in explaining the experimental results.