Abstract
We report on measurements of the transverse magnetization of a ferrofluid rotating as a rigid body in a constant magnetic field, , applied perpendicular to the axis of rotation. The rotation of the fluid leads to a nonequilibrium situation, where the ferrofluid magnetization and the magnetic field within the sample, , are no longer parallel to each other. The off-axis magnetization perpendicular to is measured as a function of both the applied magnetic field and the angular frequency . 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 yield reasonably good shapes of the curves of transverse magnetization vs . However, like the other models, they overestimate their magnitudes.
2 More- Received 19 August 2005
DOI:https://doi.org/10.1103/PhysRevE.73.036302
©2006 American Physical Society