9 pages, 4 figuresInternational audienceThe behavior of a magnetic fluid drop lying on a solid horizontal surface and surrounded by a nonmagnetic liquid under the action of a uniform magnetic field which is rotating in a vertical plane with low frequency (of the order of 1 Hz) has been investigated experimentally. Shape deformation and translatory motion of the drop were observed and studied. The drop translation velocity for different field amplitudes and field frequencies has been measured

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Data on the formation of periodic and labyrinth structures in thin layers of a kerosene-based magnetic fluid (MF) under the action of electric and magnetic fields is given in [1,2]. In this paper, we analyze the possible reasons and mechanisms of the observed phenomenon and present new experimental results concerning the structurization processes in the MF. The total set of the existing data enables us to state that the magnetic ordering of single-domain particles in aggregates is possible. EXPERIMENTAL METHOD AND OBJECT OF RESEARCHTo study the structures formed and their transformation under the effect of various factors, we used the diffraction scattering of a He-Ne laser beam perpendicular to a thin layer of the MF. The scheme of the experimental setup is thoroughly described in [2]. The intensity of the scattered light was measured by a photoelectric detector (type FES-25) with a diaphragm or by a miniature photoresistor, depending on the actual aims of the experiment. The measuring cell consisted of two rectangular glass plates with a transparent conducting coating. A fluoroplastic film with a circular hole in the center was placed between the glass plates; this hole was filled with the MF in question. The thickness of the MF layer amounted to 20-40 µ m and was determined by the thickness of the fluoroplastic films. To generate the electric field, voltage from a stabilized d.c. source was applied to the plates. As the magnetizing system, we used Helmholtz coils generating a uniform field in a volume several times larger than that of the cuvette. The same cuvette was also used for visual optical-microscopic observation of the processes in the MF. To study one of the structure-sensitive parameters of the MF, its magnetic susceptibility, the bridge method was used.The magnetic susceptibility was calculated according to the change in the inductance of the measuring solenoid caused by the sample placed into it. The inductance was measured by an LCR-817 immittance meter at a measuring field frequency of 70 Hz; the error did not exceed 0.1%. The object of study was a kerosenebased MF with magnetite particles stabilized by oleic acid. The volume concentration of the dispersed phase was 11%; the dynamic viscosity amounted to 5 × 10 -3 Pa s. EXPERIMENTAL RESULTS AND DISCUSSIONEarlier studies [2] showed that periodic structural lattices can be formed in thin MF layers in an electric field in the near-electrode space and can be transformed following a change in the external conditions. The formation of structural lattices was observed when a certain (critical) voltage at the electrodes was reached. Its value depended on the temperature and the intensity of the applied magnetic field. It was concluded that the structural transformations can be interpreted as phase transitions in disperse systems. Such an interpretation of structural transformations in MFs was earlier proposed in many studies (e.g., see [3][4][5]).Meanwhile, our experimental investigations showed that stabilized kerosene-based MFs are sufficiently stable ...