Instability of a thin layer of a magnetic fluid in a perpendicular magnetic field

The instability and disintegration of a thin layer of a magnetic fluid in a perpendicular magnetic field are considered. New experimental findings for the dependence of the resulting surface structure of the layer on the external magnetic field and thickness of the layer are reported. Light diffraction by such structures is studied. Experimental data are compared with today’s theoretical concepts.     

Rosenzweig instability in a thin layer of a magnetic fluid

A simple mathematical model of the initial stage of nonlinear evolution of the Rosenzweig instability in a thin layer of a nonlinearly magnetized viscous ferrofluid coating a horizontal nonmagnetizable plate is constructed on the basis of the system of equations and boundary conditions of ferrofluid dynamics. A dispersion relation is derived and analyzed using the linearized equations of this model. The critical magnetization of the initial layer with a flat free surface, the threshold wavenumber, and the characteristic time of evolution of the most rapidly growing mode are determined. The equation for the neutral stability curve, which is applicable for any physically admissible law of magnetization of a ferrofluid, is derived analytically.     

Development of the Rayleigh-Taylor instability in a thin layer of a magnetic fluid subjected to an orthogonal magnetic field

A thin layer of a Newtonian magnetic fluid wetting the faced-down surface of a horizontal magnetized plate in a vertical magnetic field is considered. The lower boundary of the layer is the interface with a stationary gas. The effect of magnetic forces on the development of the Rayleigh-Taylor instability is considered in the linear formulation of the long-wave approximation of ferrohydrodynamic equations.     

Dynamics of nanoparticle agglomeration in a magnetic fluid in a varying magnetic field

It is found that the dependence of the magnetic nanoparticle agglomerate length in a magnetic fluid on the applied magnetic field has three characteristic segments: a substantial increase in the agglomerate length with the magnetic field in the range of weak fields, a segment with an insignificant increase in the average length of agglomerates upon an increase in the field, and a sharp increase in the agglomerate length with a further increase in the field. It is shown that the agglomerate length increases in the range of strong magnetic fields due to a decrease in the spacing between adjacent agglomerates down to their complete coalescence. The total number of agglomerates decreases thereby.     

Behavior of an electron plasma in a thin metallic slab placed in a variable electric field

The response of an electron plasma in a thin metallic slab to a variable electric field applied normally to the slab surface is studied in the framework of the kinetic theory. The radiation power absorbed by a unit surface area is calculated under the assumption that the electric field frequency is small compared with the plasma frequency and that electron scattering by the metal surface is of a purely diffuse character.     

Distortions of the magnetic structure of a thin antiferromagnetic layer in magnetic field

Distortions induced by an external magnetic field in the magnetic structure of a thin layer of a uniaxial collinear antiferromagnet with rough surfaces are studied using computer simulation. It is shown that, under certain conditions, the presence of atomic steps at the layer surfaces causes the antiferromagnetic layer to break up into domains. The character and magnitude of distortions are found for an arbitrary ratio of the distance between atomic steps to the order parameter correlation length. Original Russian Text ? A.I. Morosov, I.A. Morosov, A.S. Sigov, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 7, pp. 1228–1235.     

Dynamics of a dielectric droplet suspended in a magnetic fluid in electric and magnetic fields

The behavior of a microdrop of dielectric liquid suspended in a magnetic fluid and exposed to the action of electric and magnetic fields is studied experimentally. With increasing electric field, the deformation of droplets into oblate ellipsoid, toroid and curved toroid was observed. At the further increase in the electric field, the bursting of droplets was also revealed. The electrorotation of deformed droplets was observed and investigated. The influence of an additional magnetic field on the droplet dynamics was studied. The main features of the droplet dynamics were interpreted and theoretically examined.     

Dynamics of a nonmagnetic drop suspended in a magnetic fluid in a rotating magnetic field

The behavior of a nonmagnetic drop suspended in a magnetic fluid and subjected to the action of a rotating magnetic field is studied experimentally. The configurations of the drop in the form of prolate and oblate ellipsoids of revolution in the rotating field are investigated, and disintegration of the drop in the rotating field and the development of comb instability of its surface under certain conditions are observed.     

On the self-organization of atomic magnetic moments after application of an electric field

An attempt is made to reveal the self-organization of atomic magnetic moments in rare-earth ferrimagnets of the TbFe₂ type, an effect reported on in the works of S.K. Godovikov. A careful experimental study and a critical analysis of the data reported in his publications suggest that there are no grounds to maintain that this phenomenon exists.     

Instability and breakup of a thick layer of a viscous magnetic fluid in a tilted magnetic field

A linear partial differential equation describing the evolution of an initial disturbance of a flat free surface of a thin layer of a viscous magnetic fluid covering a horizontal plate in the presence of a uniform magnetic field, is derived within a system of ferrohydrodynamic and magnetostatic equations. The effect of magnetizing the plate on the stability of the flat free surface is investigated. An estimate is obtained for the minimum value of the tangential component of the magnetization vector of the fluid sufficient to radically alter the pattern of the final breakup of the continuous layer. Zh. Tekh. Fiz. 69, 14–22 (October 1999)     

Electrodynamic response of a nanosphere placed in a magnetic field

Absorption of electromagnetic radiation by 2D electrons at the surface of a quantum sphere placed in a weak magnetic field is studied. It is shown that at low temperatures, the absorption curve exhibits four resonance peaks observed in the Faraday geometry (photon wave vector parallel to the magnetic field) and six peaks in the Voigt geometry (photon wave vector perpendicular to the magnetic field). In the particular case of the Voigt geometry, where the photon polarization vector is parallel to the magnetic field, the absorption curve exhibits only two resonance peaks. The shape, position, and intensity of the peaks are examined. It is shown that at temperatures close to zero, steps of two types appear in the absorption curve. One type of steps is associated with crossing of the μ-?ω level by the electron energy levels, while steps of the other type arise when electron energy levels cross the chemical potential μ.     

Stabilization of electromagnetic solitons in thin films of topological insulators by constant electric field

We consider the propagation of a variable electromagnetic field in a thin film of a topological insulator in low temperatures case at the presence of electric field. As a result we obtain an effective equation on the vector-potential amplitude of a variable electromagnetic field. We also detect some solutions, corresponding to solitons in the case of a cosine-type dispersion law for electronic subsystem. Finally, we analysed how non-linear solutions depend on the parameters of the problem and on electrostatic field.     

Bending of the magnetic fluid surface in the electric field of a plane capacitor

The behavior of magnet particles in an insulating fluid exposed to an electric field is studied. The surface of the fluid in the electrode gap changes because of the space charge forming in the near-electrode layer.     

The shape of a drop in a constant electric field

The variation of the shape of a drop immersed in an immiscible liquid under the action of an electric field is calculated. The charge is transferred both by ohmic current through the interface and by the convective component over the interface. A solution quadratic in the parameter that is the ratio of the electric pressure to the capillary pressure is analyzed. Conditions where the drop transforms into a spheroid that is prolate or oblate along the electric field vector are found. An experimental study of the drop deformation by electric forces is carried out.     

Dilation analyticity in constant electric field

The resolvent of the operatorH ₀(ε, θ)=?Δe ^-20+εx ₁ e ^θ is not analytic in θ for θ in a neighborhood of a real point, if the electric field ε is non-zero. (One manifestation of this singular behavior is that for 0<|Im θ|<π/3,H ₀(ε, θ) has no spectrum in the finite plane.) Nevertheless it is shown that the techniques of dilation analyticity still can be used to discuss the long-lived states (resonances) of a system described by a Hamiltonian of the formH=?Δ+εx ₁+V(x).     

Bloch electrons in constant electric field

The motion of a conduction electron of a crystal in a constant electric field is studied. It is shown that the modulus of the wave function inp-representation is well approximated by a periodic function for times smaller than several hundred periods.On leave from Department of Physics, Luminy, Université d'Aix-Marseille II, and Centre de Physique Théorique, CNRS, Marseille, France