Kinetics of ordering in ferrofluid studied by polarised neutron beam

V. T. Lebedev¹ - Gy. Török² - G. P. Gordeev¹ - L. A. Axelrod¹ - I. M. Lazebnik¹

¹ Petersburg Nuclear Physics Institute 188300 Gatchina, St.Petersburg dist., Russia
² Research Institute for Solid State Physics and Optics P.O.Box 49, H-1525 Budapest, Hungary

Abstract
Kinetics of ferrofluid ordering in magnetic field and the decay of particles magnetic correlation after field switching off have been investigated by neutron polarisation analysis. At ambient temperature, the long-time relaxation of magnetic scattering intensity I_m ∼ − ln(t/τ_L) with a time τ_L ∼ 4·10⁷ s proves the existence of metastable clusters. The fluid with CoFe₂Ø₄-grains, examined by a sharp neutron beam, revealed the magnetic correlation of particles, nearby the interface and free surface, inducing extra-magnetisation of surface regions extended to a few mm from the border to the volume. Figs 3, Refs 10.