Ba-ferrite particles for magnetic liquids with enhanced Néel relaxation time and loss investigations

R. Müller¹ - R. Hiergeist¹ - W. Gawalek¹ - A. Hoell²

¹ Institut für Physikalische Hochtechnologie e.V. Jena, D-07745 Jena, Germany
² Hahn-Meitner-Institut, D-14109 Berlin, Germany

Abstract
Nanometer-scale particles are interesting because of their unique magnetic properties. Barium ferrite with particle sizes \lessapprox 10 nm behave superparamagnetically and show at bigger sizes the transition to single domain behaviour. Beside the particle size, the anisotropy energy K₁·V, and thus the Nèel relaxation time, depends also on the amount of doping. The glass crystallisation method was used for preparation of different Ba-ferrites. Ferrofluids have been prepared using Isopar^\circledR M or dodecane as a carrier liquid. Magnetic parameters were obtained by VSM, hysteresis losses (specific loss power) of ferrite powders by a hysteresometer at 50 Hz. Magnetic core sizes were calculated from hysteresis loops. SANS curves of a ferrofluid reveal single magnetic particles and aggregated magnetic particles with an incomplete organic shell. Figs 3, Refs 9.