Sensors and Actuators A: Physical

A concise and factual abstract is required. The abstract should state briefly the purpose of the research, the principal results and major conclusions. An abstract is often presented separately from the article, so it must be able to stand alone. For this reason, References should be avoided, but if essential, then cite the author(s) and year(s). Also, non-standard or uncommon abbreviations should be avoided, but if essential they must be defined at their first mention in the abstract itself.

Physica. B, Condensed matter

Major recent advances Magnetic fluid rheology and flow advances in the past year include: (1) generalization of the magnetization relaxation equation by Shliomis and Felderhof and generalization of the governing ferrohydrodynamic equations by Rosensweig and Felderhof; (2) advances in such biomedical applications as drug delivery, hyperthermia, and magnetic resonance imaging; (3) use of the antisymmetric part of the viscous stress tensor due to spin velocity to lower the effective magnetoviscosity to zero and negative values; (4) and ultrasound velocity profile measurements of spin-up flow showing counter-rotating surface and co-rotating volume flows in a uniform rotating magnetic field. Recent advances in magnetic fluid rheology and flows are reviewed including extensions of the governing magnetization relaxation and ferrohydrodynamic equations with a viscous stress tensor that has an antisymmetric part due to spin velocity; derivation of the magnetic susceptibility tensor in a ferrofluid with spin velocity and its relationship to magnetically controlled heating; magnetic force and torque analysis, measurements, resulting flow phenomena, with device and biomedical applications; effective magnetoviscosity analysis and measurements including zero and negative values, not just reduced viscosity; ultrasound velocity profile measurements of spin-up flow showing counter-rotating surface and co-rotating volume flows in a uniform rotating magnetic field; theory and optical measurements of ferrofluid meniscus shape for tangential and perpendicular magnetic fields; new theory and measurements of ferrohydrodynamic flows and instabilities and of thermodiffusion (Soret effect) phenomena.

Magnetic fluid rheology and flows

It is shown that the magnetic dynamics of an assembly of nanoparticles dispersed in a viscous liquid differs significantly from the behavior of the same assembly of nanoparticles immobilized in a solid matrix. For an assembly of magnetic nanoparticles in a liquid two characteristic mode for stationary magnetization oscillations are found that can be called the viscous and magnetic modes, respectively. In the viscous mode, which occurs for small amplitude of the alternating magnetic field H0 as compared to the particle anisotropy field Hk, the particle rotates in the liquid as a whole. In a stationary motion the unit magnetization vector and the director, describing the spatial orientation of the particle, move in unison, but the phase of oscillations of these vectors is shifted relative to that of the alternating magnetic field. Therefore, for the viscous mode the energy absorption is mainly due to viscous losses associated with the particle rotation in the liquid. In the opposite regime, H0 ≥ Hk, the dir...

Dynamics of magnetic nanoparticle in a viscous liquid: Application to magnetic nanoparticle hyperthermia

Fil: de Sousa, Maria Elisa. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Instituto de Fisica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Fisica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Fisica; Argentina

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Stability and Relaxation Mechanisms of Citric Acid Coated Magnetite Nanoparticles for Magnetic Hyperthermia

http://www.tara.tcd.ie/bitstream/handle/2262/48879/Microwave%20absorbent%20properties%20of%20nanosized%20cobalt%20ferrite%20powders%20prepared%20by%20coprecipitation%20and%20subjected%20to%20different%20thermal%20treatments.pdf?sequence=1

Microwave absorbent properties of nanosized cobalt ferrite powders prepared by coprecipitation and subjected to different thermal treatments

Two powder samples of manganese ferrite (MnFe2O4) with different morphology and particle size 30–40 nm, denoted by A and B have been synthesized by different methods starting from MnCl2·4H2O and FeCl3·6H2O. Sample A was obtained by co-precipitation followed by calcination at 900 °C and sample B has been obtained by hydrothermal method. XRD analysis show that calcination leads to the occurrence of other phases than MnFe2O4, therefore the hydrothermal method gives better results. From the temperature dependence of the electrical resistivity, measured over the range 300–483 K, the activation energy, Δ E , of the investigated samples has been evaluated, resulting in 0.43 eV (for sample A) and 0.32 eV (for sample B). The conductivity mechanism in the samples was explained in terms of Mott's variable range hopping (VRH) model. The results showed that the density of states at the Fermi level is constant over the investigated temperature range, being in order of 0.788 × 10 17 eV − 1 cm − 3 (for sample A) and 2.05 × 10 17 eV − 1 cm − 3 (for sample B). The hopping distance, R and the hopping energy, W (parameters of VRH model) have also been computed. Room temperature values are R=27.08 nm and W=152 meV for sample A and R=21.29 nm and W=120 meV for sample B.

The electrical properties of manganese ferrite powders prepared by two different methods

Measurements performed over the frequency range 700 MHz to 3 GHz, of the complex dielectric permittivity of (i) a kerosene-based magnetic fluid sample with magnetite particles stabilized with oleic acid, (ii) oleic acid and (iii) kerosene, are presented. The biphasic dielectric model describing the dielectric behaviour of magnetic fluids was redefined based on the experimental results of Rocchiccioli-Deltcheff et al. According to this proposed new model, the magnetic fluids can be considered as being biphasic systems in which one phase consists of surfacted colloidal particles electrically charged by adsorbed or chemisorbed ions and the other phase consists of the carrier liquid. Using the Sillars theory for heterogeneous dielectrics, in the biphasic approximation, we have determined the dielectric permittivity, electric conductivity and shape factor of the colloidal magnetite particles within the investigated magnetic fluid, in the microwave range. The values obtained for the colloidal magnetite particles are the shape factor n = 2.27, the real part of the dielectric permittivity e1' = 36.8, and the effective conductivity σ1 eff = 1.5 Ω−1 m−1. The differences between the experimental results and the values of conductivity and permittivity of bulk magnetite are explained in terms of the proposed biphasic model.

http://iopscience.iop.org/article/10.1088/0953-8984/19/3/036104/pdf

Microwave dielectric properties of magnetite colloidal particles in magnetic fluids

Starting from the Landau–Lifshitz equation, with resonant frequency f0 = ω0/2π ,i t is dem onstrated that, in the case of a magnetic fluid, the measured resonant frequency, fres is always different from f0 ,e xcept for the case of pure resonance (i.e. zero damping paramete ro f Landau–Lifshitz equation) where fres = f0 .I t is also s hown that fres and the corresponding maximum absorption frequency, fmax ,a re different, thus supporting the deductions of Scaife, who arrived at this conclusion using an alternative theoretical approach. Furthermore, based on complex magnetic susceptibility measurements, over the frequency range 100 MHz–6 GHz, the dependence of the ratio fmax/fres on an external polarizing magnetic field, Hpol, over the approximate range 0 and 1.3 kOe and on particle concentration has been examined for different magnetic fluid samples. It is demonstrated how the ratio fmax/fres tends to unity both by (i) increasing the polarizing field and (ii) decreasing the particle concentration of the samples.

/pdf/the-influence-of-particle-concentration-and-polarizing-field-4gjucjmo5c.pdf

Catalin Nicolae Marin

Papers

Microwave absorbent properties of nanosized cobalt ferrite powders prepared by coprecipitation and subjected to different thermal treatments

The electrical properties of manganese ferrite powders prepared by two different methods

Microwave dielectric properties of magnetite colloidal particles in magnetic fluids

The influence of particle concentration and polarizing field on the resonant behaviour of magnetic fluids

Dielectric Behavior of Some Ferrofluids in Low-Frequency Fields