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15 May 2005

Volume 97, Issue 10, Articles (10xxxx)

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back to top Magnetic Fluids and Sensors

Magnetoelectric effect in sputtered composites

Simon Stein, Manfred Wuttig, Dwight Viehland, and Eckhard Quandt

J. Appl. Phys. 97, 10Q301 (2005); http://dx.doi.org/10.1063/1.1846631 (3 pages) | Cited 11 times

Online Publication Date: 17 May 2005

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The magnetoelectric effect in millimeter size PMN-PT∕Terfenol-D composites is known. In an effort towards miniaturization, we report on the magnetoelectric effect in micrometer-size sputtered composites. Multilayers of TbFe/FeCo with a thickness of 4 μm were sputter deposited on both sides of PMN-PT piezoelectric single crystals. The magnetoelectric voltage of samples was measured and reached values of 13 mV/(Oe cm) at dc bias fields of 2 mT, a linear dependence of magnetoelectric voltage on ac amplitude was detected in the range from 1 mT to 1 nT.
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75.50.Bb Fe and its alloys
81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.80.+q Magnetomechanical effects, magnetostriction
81.15.Cd Deposition by sputtering

Effective magnetoviscosity of planar-Couette magnetic fluid flow

Xiaowei He, Shihab Elborai, Dokyung Kim, Se-Hee Lee, and Markus Zahn

J. Appl. Phys. 97, 10Q302 (2005); http://dx.doi.org/10.1063/1.1850337 (3 pages) | Cited 2 times

Online Publication Date: 17 May 2005

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Magnetic fluid spin velocity, shear stress, and magnetoviscosity were calculated for a planar-Couette magnetic fluid flow, with applied uniform dc magnetic field transverse to the duct axis and by using Shliomis’ first magnetization relaxation equation, generally valid for low magnetic fields. For simplicity, the magnetic fluid was assumed to be linearly magnetizable with constant magnetic susceptibility. Using the assumption of incompressible flow and the symmetry of the geometry, the solution for the axial flow is a linear function of position within the channel while the spin velocity is spatially constant, where both the spin velocity and the change in viscosity, obey a third order algebraic torque equation due to an imposed magnetic field H or a fifth order algebraic torque equation due to the imposed magnetic flux density B. This analysis describes the conditions for multivalued effective magnetoviscosity and spin velocity.
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75.50.Mm Magnetic liquids
47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.15.-x Laminar flows
75.40.Mg Numerical simulation studies
75.30.Cr Saturation moments and magnetic susceptibilities

Self-forming, quasi-two-dimensional, magnetic-fluid patterns with applied in-plane-rotating and dc-axial magnetic fields

S. Elborai, D.-K. Kim, X. He, S.-H. Lee, S. Rhodes, and M. Zahn

J. Appl. Phys. 97, 10Q303 (2005); http://dx.doi.org/10.1063/1.1851453 (3 pages) | Cited 5 times

Online Publication Date: 17 May 2005

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We report flow instabilities with simultaneous, in-plane-rotating and dc-axial uniform magnetic fields. In uniform dc-axial magnetic fields, a ferrofluid drop in a Hele-Shaw cell with an ∼ 1.0-mm gap forms the familiar labyrinth pattern. With subsequent application of an ∼ 100-G rms in-plane, 20–40-Hz rotating uniform magnetic field, smooth spirals form. If the rotating magnetic field is applied first, the drop holds together for low dc-axial magnetic fields and no labyrinth pattern develops. If the dc magnetic field is subsequently increased above a threshold value, the ferrofluid drop abruptly transforms into many ferrofluid droplets arranged in a regular pattern.
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75.50.Mm Magnetic liquids
68.15.+e Liquid thin films
47.20.Hw Morphological instability; phase changes
47.54.-r Pattern selection; pattern formation
47.65.-d Magnetohydrodynamics and electrohydrodynamics

Static and dynamic properties of magnetic nanowires in nematic fluids (invited)

C. Lapointe, N. Cappallo, D. H. Reich, and R. L. Leheny

J. Appl. Phys. 97, 10Q304 (2005); http://dx.doi.org/10.1063/1.1852171 (6 pages) | Cited 13 times

Online Publication Date: 17 May 2005

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Microscopy experiments are employed to characterize the elastic interactions of magnetic nickel nanowires suspended in a nematic liquid crystal. The nematic imposes a torque on an isolated wire that increases linearly with the angle between the wire and the nematic director in a manner quantitatively consistent with predictions based on an analogy between the nematic elasticity and electrostatics. An extension of this analogy also explains a measured orientation-dependent repulsive force between a wire and a wall. The angular relaxation of a wire in response to the elastic torque displays a nonexponential time dependence from which effective viscosities for the fluid are determined. The behavior of a wire in a twisted nematic cell further demonstrates how spatial variations in the director can convert the torque to a controlled translational force that levitates a wire to a specified height.
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75.50.Mm Magnetic liquids
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.75.-c Magnetic properties of nanostructures
75.30.Gw Magnetic anisotropy
66.20.-d Viscosity of liquids; diffusive momentum transport
62.10.+s Mechanical properties of liquids
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Effects of surfactant friction on Brownian magnetic relaxation in nanoparticle ferrofluids

Alexandre B. Pakhomov, Yuping Bao, and Kannan M. Krishnan

J. Appl. Phys. 97, 10Q305 (2005); http://dx.doi.org/10.1063/1.1855195 (3 pages) | Cited 8 times

Online Publication Date: 17 May 2005

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Measurement of the variation of relaxation frequency of Brownian rotation of magnetic nanoparticles in a ferrofluid due to binding of organic molecules is a possible tool for detection of biomolecules in solution. We investigate frequency- and temperature-dependent magnetic behavior of model ferro-fluids of surfactant-coated Co nanoparticles, 20 nm in diameter, in dichlorobenzene in a wide concentration range. At room temperature the most diluted ferrofluids have a single relaxation frequency determined by the fluid viscosity and effective particle volume. Increasing concentration leads to an appearance of the second, low-frequency relaxation peak, attributed to the effective viscosity associated with interparticle friction.
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75.50.Mm Magnetic liquids
75.50.Cc Other ferromagnetic metals and alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Cr Saturation moments and magnetic susceptibilities
87.50.C- Static and low-frequency electric and magnetic fields effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Lr Magnetic aftereffects
82.70.Uv Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions)
75.75.-c Magnetic properties of nanostructures

Self-consistent model of field gradient driven particle aggregation in magnetic fluids

O. Hovorka, B. Yellen, N. Dan, and G. Friedman

J. Appl. Phys. 97, 10Q306 (2005); http://dx.doi.org/10.1063/1.1860811 (3 pages) | Cited 3 times

Online Publication Date: 17 May 2005

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Particle aggregation in magnetic colloids driven by strong magnetic field gradients is studied using self-consistent field calculations. The model takes into account field screening due to average fluid magnetization and demagnetizing field arising from spatially varying magnetic particle concentration. Solutions for the problem of particle aggregation due to a single magnetic pole demonstrate that, in high particle concentration, the magnetic field must be calculated self-consistently.
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75.50.Mm Magnetic liquids
82.70.Dd Colloids
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Mg Numerical simulation studies
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