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This article presents a new method of excitation for a fast-changing rotating magnetic field (RMF) of higher frequencies (HF) causing the hyperthermic effect in magnetic fluids. The method proposed here uses a magnetic field exciter (inductor) consisting of a ferrite magnetic circuit and a system of coils connected in a two-phase arrangement. The proposed system is powered by two higher-frequency rectangular signals, with a 90-degree phase shift between each other, through HF transformers with ferrite cores. This paper presents the outcomes of the operation of RMFs in the frequency range of 38 kHz to 190 kHz, with a value of amplitude of magnetic field intensity H equal to 20 kA/m and increasing temperature, in a sample of APG513 magnetic liquid. The obtained results show that, in the range of the magnetic field intensities of moderate values, at a constant frequency f, the values of the time derivative of temperature are proportional to the square of the magnetic field intensity dT/dt~H2. Moreover, the values of the temperature rate, which are measured with the constant value of the magnetic field intensity, are proportional to the square of the frequency dT/dt~f2. At higher amplitudes of the RMF, the relationship dT/dt~H2 is no longer fulfilled, and an inflexion point of this function appears. In the case of the highest values of the achieved intensity amplitudes (H = 20 kA/m), the parameter of the Langevin function achieves a value equal to ξ = 6.

The article describes the necessary conditions for the phenomenon of thermal energy release in a magnetic fluid placed in a high-frequency rotating magnetic field. The minimum amplitude of the magnetic field was calculated and the thermal power released (by the rotating spherical nanoparticles in the viscous medium) was estimated. The estimations were based on the assumption that the magnetic relaxation times (τN and τB) and the magnetic field rotation period (τrot) meet the condition: τN>>τrot>>τB. The principle of operation and construction of the device generating a high-frequency rotating magnetic field is described. Preliminary experimental studies were carried out using a magnetic fluid with magnetite nanoparticles that indicated magnetic relaxation as the cause of the released heat. The value of the absorption rate in the experiment and its dependence on the strength of the magnetic field were determined.

The article describes the effect of magnetic hyperthermia under the influence of an oscillating magnetic field acting on the colloidosomal iron oxide nanoparticle clusters with dimensions of ≅ 100 nm containing magnetite nanoparticles ≅ 11.8 nm. The experiment was carried out at the magnetic field frequency f = 355 kHz at various amplitude values up to H = 20 kA·m−1. The nature of the heating curves shows that the main mechanism of heating is the effect of magnetic relaxation. The general construction of apparatus generating an oscillating magnetic field is described. The specific loss power (SLP) value was determined in the experiment.

The article presents the results of research on the effect of magnetic hyperthermia performed on agar gel samples containing magnetite nanoparticles coated with dextran polymers for different molar weight M (150 kDa, 70 kDa, and 40 kDa). Regardless of the difference in molar dextran weights, these samples differed in a mass concentration of nanoparticles in the ferrogel C0 (1.602 mg/cm3, 2.506 mg/cm3, 3.311 mg/cm3, and 4.218 mg/cm3). In the case of the highest magnetic field value H (20 kA·m−1), the specific loss power SPL reaches 70 W·g−1 for nanoparticles with 150 kDa dextran at a concentration of nanoparticles C0 = 1.602 mg/cm3. An oscillating magnetic field with an amplitude up to 20 kA·m−1 and a frequency of 357 kHz was used in the study.

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 physical principles of magnetic hyperthermia are based on the heat generation of magnetic nanoparticles under the influence of applied magnetic fields of different configurations. The choice of a suitable methodology for generating a magnetic field can significantly affect the resulting thermal effect and thus the efficiency itself. The technical details of the apparatus generating a rotating magnetic field and a comparison of the efficiency when the alternating magnetic field is applied are analyzed. While the mechanism of the temperature rise is the same, as shown by the fitting of the dT/dt curves, the intrinsic loss power differs significantly. It was found that the rotating magnetic field produces a thermal effect that is more than twice that of the alternating magnetic field under similar experimental conditions.

Structure characterization of the initial magnetosome chain solution (IM) and mechanically treated magnetosome solution (SM) was conducted by dynamic light scattering (DLS), small-angle neutron (SANS) and X-ray (SAXS) scattering. Experimental scattering curves of magnetosome IM and SM samples indicate the presence of polydisperse particles in the investigated solutions. Predominant amount of non-magnetic components (most probably lipids) was found from SANS contrast variation experiment. The values of forward scattering intensities confirm the differences in average sizes of samples prepared by various methods. The effect of sonication and filtering on size distribution and polydispersity was also confirmed by evaluating of hydrodynamic size distribution. This fact causes that SM sample magnetically behaves in a different manner showing that energy losses and specific absorption rate are noticeable reduced, and that indicates variation in the relaxation process and heat distribution.

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.

This paper presents the results of the heating of magnetic fluid (MF) containing magnetite nanoparticles. Volume concentration of magnetite nanoparticles ( ϕ V = 2.76%) was determined from magnetic experiments. Mean diameter 〈 d 〉 = 12.7 nm and its standard deviation s = 5.0 nm of the core of magnetic particles were obtained using TEM technique. Magnetic fluid heating experiments were carried out at a frequency of 440 kHz for magnetic field strength up to 3 kA⋅m −1 using lab-made experimental set-up. For temperature measurements, various kinds of devices were used: pyrometer, thermocouple thermometer, optical fiber temperature sensor and thermometer with ultrasonic sensor. Specific absorption rate (SAR) and temperature measurement error were calculated and discussed for all the thermometers used. The influence of eddy currents induced in a thermocouple on the determination of temperature of MF was described. The usefulness of different types of temperature measuring devices and their accuracy in determining the heating rate and the SAR coefficient of the magnetic fluid were analyzed and discussed.

Properties of Magnetosome Suspension under the In uence of Magnetic Field A. Jozefczak, M. Mol£an, Z. Rozynek, T. Hornowski, A. Skumiel, M. Timko, J. Tothova, P. Kop£anský and B. Leszczy«ski Institute of Acoustics, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Pozna«, Poland Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01 Ko2ice, Slovakia Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland Department of Physics, NTNU, Hogskoleringen 5, NO-7491 Trondheim, Norway Department of Physics, Technical University of Ko2ice, Park Komenskeho 2, 042 00 Ko2ice, Slovakia NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614 Pozna«, Poland

Ultrasonic emulsifying processes of immiscible liquids can be used to obtain stable emulsions. The authors used an ultrasonic sandwich head with an energy concentrator to obtain a suitable value of the energy density necessary for the emerge of ultrasonic cavitation. Two piezoelectric ring (Dext = 50 mm) transducers of Pz-26 type produced by FERROPERM were used to design the ultrasonic sandwich head. The frequency of the ultrasonic wave was 18.4 kHz and the excitation time of the ultrasonic transducer exiting 5 minutes. Visible bubbles during the generation of ultrasonic waves appeared in the mixture after exceeding the cavitation threshold. The authors determined also the cavitation threshold by measuring the electrical voltage conducted to the transducers. To receive long-lasting emulsion, the electrical voltage attained 300 Vpeak. The dispersion dependence on the emulsifying time was determined. The emulsion of linseed oil and water was stable through some months without surfactants.

The temperature dependence of the particle size distribution (PSD) of the magnetic fluid with an additional biocompatible dextran layer was studied using a ultrasonic method. The measurements of the ultrasound velocity and attenuation were carried out as a function of the volume concentration of magnetite particles at temperatures ranging from 15°C to 40°C. In order to extract the PSD from ultrasonic measurements, the theoretical model of Vinogradov-Isakovich was used. The extraction of PSD from the ultrasonic data requires also the measurements the density and viscosity of the ferrofluid samples. The calculated PSD of the magnetic fluid with an additional biocompatible layer shows a greater thermal stability than that of a magnetic fluid with a single surfactant layer.

The magnetic properties and hyperthermia effect were studied in a magnetorheological fluid (MRF) containing iron particles of $$1 \upmu \mathrm{m}\, \text{ to}\, 5 \,\upmu \mathrm{m}$$ in diameter. The measurements showed that the magnetization in the saturation state reaches a value of 171 $$\text{ A}\cdot \text{ m}^{2}\cdot \mathrm{kg}^{-1}$$ with very small values of coercivity and remanence. They also showed the ferromagnetic behavior in the system together with a value of the magnetic susceptibility of 1.7. Theoretical and experimental results of the calorimetric effect investigation under a changeable magnetic field of high frequency ( $$f = 504$$ kHz) in an MRF will be presented in the article. The sample was subjected to an alternating magnetic field of different strengths ( $$H = 0$$ to 4 $$\text{ kA}\cdot \text{ m}^{-1})$$ . It results from a theoretical analysis that the heat power density (released in the MRF sample) referenced to the eddy current is proportional to the square of frequency, the magnetic field amplitude, and the iron grain diameter. Experimental results indicate that there are some reasons for the released heat energy such as: energy losses from magnetic hysteresis and eddy currents induced in the iron grains. If the magnetic field intensity amplitude grows, the participation of losses connected with magnetic hysteresis is increased. From the calorimetric measurements, the conclusion is as follows: for a magnetic field $$H

The magnetic properties and hyperthermia effect were studied in solution of magnetosomes obtained by changing conditions during biomineralization of magnetotactic bacteria Magnetospirillum sp.AMB-1. It was shown that adding a higher amount of Wolfe's vitamin solution (WVS) or ferric quinate (FQ) cause increase of the mean diameter from 47 nm (normal condition) up to 52 nm and 58 nm respectively. As a consequence of this change the preparation conditions coercivity and Specific Absorption Rate (SAR) increased up to 20 Oe and 949 W/gFe for sample FQ, respectively. On the other hand the process of cultivation at the changed conditions markedly reduced the cultivation time. Also the isolated chains of magnetosome were shorter containing less amount of magnetosomes too.

Ferromagnetic and superparamagnetic nickel nanocrystallites, stabilized in a carbon matrix, were prepared by a three-step procedure including formation of a Ni acrylamide complex, followed by frontal polymerization and pyrolysis of the polymer at various temperatures. It was found that the procedure applied enables fab- rication of magnetic beads containing metallic nanocrystallites embedded in a carbon matrix. The size of the crystallites, their morphology, volume fraction, and magnetic properties can be tailored by the pyrolysis temperature. The size of the crystallites affects their behavior in an external magnetic field, i.e., a heating process is the most effective for a sample pyrolyzed at 873 K. The revealed H n -type dependence of the temperature increase rate, (dT /dt)t=0, on the amplitude of the magnetic field indicates the presence of both superparamagnetic and ferromagnetic particles in all the samples studied since n > 2. For the superparamagnetic particles, the heating mechanism is associated with Neel relaxation. For the lower values of the magnetic field amplitude, H H0 ,t he magnetic hysteresis is the main source of thermal energy losses. The composites con- taining magnetic Ni nanocrystallites entrapped in a carbon matrix can be potentially applied for hyperthermia treatment.

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.

A polymer ferromagnetic gel is an assembly of ferromagnetic nanoparticles embedded in a gel. The finely distributed magnetic particles of iron oxide (Fe3O4) were suspended, due to adhesive forces, in the flexible matrix (poly(dimethyl siloxane) PDMS). The mean diameter of the suspended nanoparticles, equal to 8.9 nm, was determined by means of a vibrating sample magnetometer. The dispersion of the electric permittivity, studied in the frequency range of 400 Hz–5 MHz, revealed the maxima at approximately 92 kHz and 2.5 MHz. The application of the homogenous magnetic field, ranging from 0 mT to 500 mT induced the anisotropy of the electric permittivity for the mutual parallel orientation of the magnetic field, electric field and the axis of the sample. For the magnetic induction B = 500 mT the highest decrease in the electric permittivity and the shift of the maximum from 2.5 toward 2.9 MHz were found.

The temperature dependence of the particle size distribution (PSD) of a transformer oil-based ferrofluid was studied using an ultrasound method. The measurements of the ultrasound velocity and attenuation were carried out in the absence of an external magnetic field as a function of the volume concentration of magnetite particles at temperatures ranging from 10 °C to 80 °C. The experimental results of ultrasound measurements were analyzed within the framework of the Vinogradov–Isakovich theory which takes into account contributions to acoustical parameters due to friction and heat exchange between magnetic particles and the surrounding carrier liquid. From the best fit of the experimental results and theoretical predictions, the parameters characterizing the PSD at different temperatures were determined. In order to analyze ultrasonic data, the density and viscosity of ferrofluid samples and the transformer oil were also measured.

This article describes the magnetic and hyperthermic investigation of a concentrated magnetic fluid on the basis of a transformer mineral oil with magnetite particles. The structure of a ferrofluid and general magnetic parameters of a medium were determined from vibrating sample magnetometer measurements. The hyperthermic experiments were carried out at a frequency f = 1500 kHz for various magnetic field amplitudes. The analysis of calorimetric results allowed an estimate of the contribution of relaxational and hysteresis loss mechanisms in total energy losses in the hyperthermic effect under the influence of an alternating magnetic field. Additional calorimetric measurements were also performed (at H C = 1500 A · m−1) versus frequency in the range from 50 kHz to 2 MHz which indicated that for f o = 653 kHz the heating process is the most effective.

The aim of this study was to investigate the influence of a poly(ethylene glycol) surface-active coating on the mechanical properties of biocompatible magnetic fluids. The coating of long-chain polymer molecules on ferrite particles serves as a protective layer that prevents agglomeration of the particles and minimizes the direct exposure of the ferrite surface to the biological environment. A useful method of studying mechanical properties of magnetic fluids is based on using ultrasound.

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).

This work is devoted to the study of heating of a biocompatible magnetic fluid due to time-varying magnetic induction. The adsorption of dextran on magnetite particles was confirmed by IR spectroscopy. A considerable thickness of the surfactant layer (oleate sodium + dextran) of about 4.3 nm prevents the formation of clusters made of nanomagnetic particles as evidenced by the fact that no maxima of the ultrasound wave absorption coefficient corresponding to cluster formation have been detected. The results show that the observed heating effect may be applied in hyperthermia treatments especially in the preferable region of 500 – 800 kHz. An “H 2– law” observed for the dependence of the SAR on the square of the amplitude of the magnetic field demonstrates the presence of superparamagnetic particles in the ferrofluid.

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.

This paper presents dynamic changes in ferrofluid properties during a magnetic field sweep. The study reported was performed on a ferrofluid with a double layer of surfactant used to prevent aggregation of particles. The ferrofluid parameters (the radius and volume of the cluster, the elastic force constant) were studied by the ultrasound wave absorption method as a function of the dynamically changing magnetic field. During the application of the magnetic field from 0 to 100 kA m(-1) the structure in the ferrofluid evolves and become anisotropic. The magnetic field was found to stimulate formation of micrometre clusters and exponential increase in the elastic force constant.

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.

In this paper acoustic and magnetic properties of water-based biocompatible fluid MF BSA (bovine serum albumin) are presented. The changes in the ultrasonic wave absorption coefficient show that MF had a good structural stability up to 100 kA/m. The measurements of magnetic susceptibility enabled to estimate the mean magnetic moment and mean size of magnetic particles. The obtained values are promising for future biomedical applications of such magnetic fluids.

An external constant magnetic field modifies the properties of magnetic fluids. This paper presents the results of an acoustic and magnetic study of a commercial ferrofluid APG 513A (FerroTec Corp.) which shows an increase in the fluid viscosity under the effect of external magnetic field. The experimental study of the effect of the viscosity induced by external magnetic field on the absorption of ultrasonic wave has been performed for a commercial ferrofluid APG 513A. The magnetic susceptibility has been also determined. The measurements enabled us to estimate the mean magnetic moment and mean size of magnetic particles.

Cobalt, iron, nickel and iron carbide nanocrystallites, stabilized within carbon beads, were prepared by the three-step procedure including formation of metal acrylamide complex, followed by frontal polymerization and pyrolysis of the polymer at various temperatures. The beads containing the nanocrystallites exhibit domination of the ferromagnetic ordering. The analysis of calorimetric results allowed estimation of the efficiency of the hyperthermal effect, under the influence of an alternating magnetic field. The XTT tests show that the extracts prepared on the basis of the Fe3C containing beads are nontoxic, whereas these made of the composites containing Co and Ni exhibit negligible cytotoxicity for the test article/vehicle ratios 6.25 and 3.125 mg/ml.

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.

Elastic constants measured by Brillouin light-scattering experiments were compared with results estimated from the pulse-echo-overlap method for the ultrasonic frequency to find dispersion in their values. In this way Brillouin hypersonic experiments complete the ultrasonic results. The present investigation includes a careful analysis of the accuracy of the results. The measured values of elastic constants suggest a weak dispersion in acoustic wave velocities. However, given the magnitude of the experimental errors, it is difficult to conclude about the dispersion.

Microscopic observations of magnetic hquids in DC magnetic field show that certain amount of colIoidal particles forms a~egates (clusters) connected into chain-like structure, (1). This internal microstructure enhances stifiess of the liquid, induces anisotropy of its mechanical properties and contributes to the dissipation of energy due to viscous and inertial interaction of clusters with surrounding liquid, A very useful md sensitive tool to study the properties of magnetic liquids and in particular the role of clusters in macroscopic behavior of liquids is the method using ultrasonic waves. However, most of the models of elastic waves in magnetic liquids do not give good agreement with basic experimental results concerning e.g. anisotropy of attenuation and phase velocity of the waves, and influence of temperature on wave parameters. The most promising description offering prediction of some of the characteristic features of wave attenuation is the model proposed by Taketomi, (2). The model takes into account, throughout semi-phenomenological considerations of energy dissipation due to clusteric motion, consequences of the microstructure of clusters for wave attenuation. Since the Taketomls model is limited to study clusteric motion at the level of balance of energy the model does not allow for easy evaluation of dispersion of waves caused by the tw~phase nature of the magnetic liquid, h the present paper a two-phase model of magnetic liquid based on a concept of superimposed continua is developed, (3). The phases are constituted by interacting clusters and surrounding liquid. The mutual interaction of clusters is represented through non-vanishing stress tensor for solid phase. The interaction of clusters with liquid expresses drug force between phases. The proposed model of ultrasonic waves is based on the two linearized balances of linear momentum for solid (s) and liquid (o phase

The influence of magnetic field on the acoustic and magnetic properties of magnetic liquids is discussed. By fitting the curve of Taketomi's theory to the experimental data of the anisotropy of ultrasonic attenuation, the values of quantities describing the structure of magnetic liquids have been determined. Moreover, the dependence of magnetic susceptibility on frequency has been measured. It shows that two processes of magnetization, based on the mechanisms proposed by Brown and Neel, contribute to the magnetization of the magnetic liquid.