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The article describes a new method of generating a rotating magnetic field of high frequency. This new measuring system is built of a magnetic circuit consisting of a ferrite torus, inside of which there are three LP windings wound on ferrite cores connected in parallel with CP capacitors. Between the three rectangular voltage signals shifted by 120 angular degrees and the LPCP circuits, three serial LSCS circuits that constitute the band-pass filter circuit are connected. In this way, the system can be powered by both sinusoidal and square signals. This significantly reduces the cost of the entire device. The necessary conditions for thermal energy release in a magnetic fluid placed in a high-frequency rotating magnetic field are given. The author presents the preliminary results of the calorimetric effect in a magnetic fluid caused by a rotating (RMF) and alternating (AMF) magnetic field. The same sample of the magnetic fluid with magnetite nanoparticles dispersed in the oil (as a carrier liquid) was studied by both methods. The heating rate temperature (dT/dt)t=0 and its dependence on the intensity and the frequency of the magnetic field was determined. Taking into account the fact that both experiments were carried out under slightly different conditions, the intrinsic loss power (ILP) was calculated in order to compare the results. They indicate that the thermal effect in RMF is more than two times greater than in AMF. This allows a significant reduction in the mass of the magnetic material needed to produce a similar thermal effect in medical applications.

The magnetic nanoparticle hyperthermia experiments require a precise system of magnetic field generation. In this article we present the design of three circuits that can generate an alternating magnetic field (the double-layer solenoid, Helmholtz coils, the inductor with C-shaped ferromagnetic core) and one system of rotating magnetic field. The theoretical calculations have been made to compare the magnetic field intensity distribution along the axis of the coils. Also the inhomogeneity of the magnetic field was determined. Similar calculations have been made for ferromagnetic core inductor. It was also shown the relationship between the intensity of magnetic field and the air gap width of ferrite core. Moreover, it was made a proposal of rotating magnetic field generator consisting of three pairs of phase-tuned inductors. In the experimental section we presented the results of calorimetric measurements performed on water dispersion of SPIONs.

Egg-shaped nanoparticles with a core–shell morphology were synthesized by thermal decomposition of an iron oleate complex. XRD and M(T) magnetic measurements confirmed the presence of FeO (wustite) and Fe3O4 (magnetite) phases in the nanoparticles. Oxidation of FeO to Fe3O4 was found to be the mechanism for the shell formation. As-made nanoparticles exhibited high values of exchange bias at 2 K. Oxidation led to decrease of exchange field from 2880 Oe (in as-made sample) to 330 Oe (in oxidized sample). At temperatures higher than the Neel temperature of FeO (200 K) there was no exchange bias. An interesting observation was made showing the exchange field to be higher than the coercive field at temperatures close to magnetite's Verwey transition.

Magnetic nanoparticles show unique properties and find many applications because of the possibility to control their properties using magnetic field. Magnetic nanoparticles are usually synthesized chemically and modification of the particle surface is necessary. Another source of magnetic nanoparticles are various magnetotactic bacteria. These biogenic nanoparticles (magnetosomes) represent an attractive alternative to chemically synthesized iron oxide particles because of their unique characteristics and a high potential for biotechnological and biomedical applications. This work presents a comparison between acoustic properties of biogenic and abiotic magnetite nanoparticle suspensions. Experimental studies have shown the influence of a biological membrane on the ultrasound properties of magnetosomes suspension. Finally the heat effect in synthetic and biogenic magnetite nanoparticles is also discussed. The experimental study shows that magnetosomes present good heating efficiency.

Water suspension of nanoparticles was studied by ultrasound spectroscopy. Nanoparticles have a core–shell structure with magnetic core Fe 3 O 4 and surfactant shells. The surface of magnetic particles was coated with oleate sodium as the primary layer and polyethylene glycol as the secondary layer. The acoustic properties of suspensions, such as velocity and attenuation of ultrasonic waves, have been measured. From experimental data mechanical properties have been determined. Adiabatic compressibility of nanoparticles suspension decreased with increase of temperature. The changes of ultrasonic wave attenuation under the influence of the external magnetic field, show that magnetic liquids with high concentration of magnetic material (despite two surfactant shells) show tendency to aggregate.

The aim of this study was to investigate the influence of poly(ethylene glycol) surface-active coating on the magnetic and thermal properties of biocompatible magnetic liquids. The data were analyzed using the high-temperature approximation model taking into account polydispersity of a system. Heating ability of the PEG-stabilized magnetic fluids was determined by the calorimetric measurement of specific absorption rate (SAR) at a frequency of 750 kHz and a magnetic field of 0–2 kA/m. MF-Oleate/PEG heating properties were found to be comparable to the ones of MF-Oleate. The PEG shell thus does not seem to effect the thermal characteristics and SAR values and might make the magnetic fluid useful for application in hyperthermia treatment.

A suspension of bacterial magnetosomes was investigated with respect to structural and magnetic properties and hyperthermic measurements. The mean particle diameter of about 35 nm was confirmed by transmission electron microscopy (TEM), X-ray and magnetic analysis. The X-ray powder diffraction peaks of magnetosomes fit very well with standard Fe3O4 reflections. The found value for specific absorption rate (SAR) of 171 W/g at 5 kA/m and 750 kHz means that magnetosomes may be considered as good materials for the biomedical applications in hyperthermia treatments. Moreover, they have biocompatible phospholipid membrane.

This paper presents acoustic properties of water-based biocompatible fluids in which magnetite particles (Fe3O4) were coated with two layers of surfactants: sodium oleate and dextran. The attenuation coefficient of ultrasonic wave measurements shows good structural stability of the fluid under the influence of a magnetic field. Hyperthermic tests proved that the magnetic fluid is suitable for therapeutic use as an agent which can release thermal energy (hyperthermia).

Magnetic susceptibility of the magnetic fluid with CoFe 2 O 4 particles was measured in the low-frequency range in order to determine mean values of the magnetic grain size and the saturation magnetisation. The volume concentration of the solid phase (CoFe 2 O 4 ) was also found. Results of the calorimetric measurements, in the range from 70 kHz to 1.7 MHz, confirmed the suitability of use of the medium studied in magnetic fluid hyperthermia, especially in the frequency region 600–800 kHz. The H 2 –law-type dependence of the specific absorption rate on the square amplitude of the magnetic field testified to the presence of superparamagnetic particles in the magnetic fluid. The minimum magnetic field intensity needed for successful hyperthermal treatment was experimentally determined.

Potential medical applications of ferromagnetic fluids whose nanoparticles are coated with biological substances, has stimulated the search for magnetic fluids of new properties. In this study the effects of double biocompatible coating of ferromagnetic nanoparticles on the properties of the ferrofluid subjected to an external magnetic field have been studied by the ultrasound method. The ultrasound wave absorption coefficient values measured have proved a good structural stability of dextran and polyethylene glycol magnetic fluids with its particles covered with two surfactant layers.

The magnetic fluids change their structure under the influence of an external magnetic field and do not return to the initial state after the magnetic field removal. It is supposed that the cluster formed in the fluid subjected to a magnetic field remains after the field has been removed. The resulting dependence of the ferrofluid properties on its magnetic history has been studied by the analysis of changes in the ultrasonic wave absorption coefficient.

An external magnetic field applied to a homogeneous magnetic fluid induces a change in its structure manifested as the appearance of chains of magnetic particles arranged along the direction of the field. This change implies changes in the acoustic and magnetic properties of the magnetic fluid such as the acoustic wave propagation velocity and coefficient of ultrasonic wave absorption, and in magnetisation. The paper reports results of a study on the influence of the magnetic field sweep rate and the magnetic fluid temperature on the value of ultrasonic wave velocity, proving that the degree of the aggregation of the magnetic particles (chain formation process) depends on the above-mentioned parameters.