title: Measuring the transverse magnetization of rotating ferrofluids.
abstract: We report on measurements of the transverse magnetization of a ferrofluid rotating as a rigid body in a constant magnetic field, H0, applied perpendicular to the axis of rotation. The rotation of the fluid leads to a nonequilibrium situation, where the ferrofluid magnetization M and the magnetic field within the sample, H, are no longer parallel to each other. The off-axis magnetization perpendicular to H0 is measured as a function of both the applied magnetic field H0 and the angular frequency Omega. The latter ranges from a few hertz to frequencies well above a characteristic inverse Brownian relaxation time. Our experimental results strongly indicate that the transverse magnetization is caused only by a small fraction of the colloidal ferromagnetic particles. The effect of the polydispersity of the ferrofluid is discussed. Experimental results are compared to predictions based on several theoretical models. A single-time relaxation approach for the so-called effective field and a field-dependent Debye relaxation of M yield reasonably good shapes of the curves of transverse magnetization vs Omega. However, like the other models, they overestimate their magnitudes.
authors.affiliation: Technische Physik, Universität des Saarlandes, 66041 Saarbrücken, Germany. jp.embs@mx.uni-saarland.de
authors.forename: J P
authors.initials: JP
authors.lastname: Embs
authors.forename: S
authors.initials: S
authors.lastname: May
authors.forename: C
authors.initials: C
authors.lastname: Wagner
authors.forename: A V
authors.initials: AV
authors.lastname: Kityk
authors.forename: A
authors.initials: A
authors.lastname: Leschhorn
authors.forename: M
authors.initials: M
authors.lastname: Lücke