Preparation and study of magnetic properties of silico phosphate glass and glass-ceramics having iron and zinc oxide

The magnetic properties of 25SiO₂–50CaO–15P₂O₅–(10−x)Fe₂O₃−xZnO (where x=0, 2, 5 mol%) glass and glass-ceramics have been studied. These glasses are prepared by melt quench technique and heat treated at 800 °C for 6 h. Electron Spectroscopy for Chemical Analysis (ESCA) revealed that the fraction of non-bridging oxygen decreases with the increase in zinc oxide content. Evolution of crystalline phases in glass-ceramics has been studied by X-ray diffraction (XRD). The microstructure as seen by scanning electron microscopy (SEM) exhibits formation of nanosize particles. Effect of controlled heat treatment on magnetic properties was studied by means of a Superconducting Quantum Interference Device (SQUID) magnetometer. Mössbauer spectroscopy at room temperature was also carried out to determine the state of iron ions in glasses and glass-ceramics. Isomer shift values of the glasses suggest that Fe³⁺ and Fe²⁺ are in tetrahedral coordination. The analysis of the glass without ZnO shows about 58 wt% of total iron ions is in the Fe³⁺ state. The samples on heat treatment show improved magnetic properties due to the formation of magnetic nanoparticles. Magnetic studies revealed the relaxation of magnetic particles and the increase in saturation magnetization with addition of 2 mol% ZnO. Increase in ZnO content results in decrease in the strength of dipolar interactions.     

Magnetic properties of the ferrimagnetic glass-ceramics for hyperthermia

Magnetic materials play a key-role in magnetic induction hyperthermia for the treatment of cancer. In this paper, we analyse the magnetic properties of ferrimagnetic glass-ceramics with the composition in the system SiO₂–Na₂O–CaO–P₂O₅–FeO–Fe₂O₃, as a function of the melting temperature. These materials were obtained by melting of commercial reagents in the temperature range of 1400–1550 °C. Room-temperature magnetic measurements were performed by means of a vibrating sample magnetometer at room temperature. The power loss was determined from calorimetric measurements, using a magnetic induction furnace. The highest power loss (61 W/g) has been obtained for samples melted at 1500 °C. The heat generation of the ferrimagnetic glass-ceramics prepared by two different synthesis methods (traditional melting and coprecipitation-derived) will be compared. These materials are expected to be useful in the localised treatment of cancer.     

Study of heating effect and acoustic properties of dextran stabilized magnetic fluid

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).     

The magnetic properties of a finite superlattice with two disordered interfaces

Within the framework of the effective field theory, based on a probability distribution technique, we examine the critical and compensation behaviors of a ferrimagnetic alternating superlattice on a simple cubic structure. The superlattice consists of k unit cells each of which consists of L layers of spin-1/2 A atoms, L layers of spin-1 B atoms and a disordered interface with two layers in between that is characterized by a random arrangement of A and B atoms A_pB_1−pA_1−pB_p with a negative coupling A − B. Considering a finite and infinite superlattices, the effect of the thickness of the film and the surface exchange coupling on the magnetic properties are studied. The obtained results show a number of characteristic phenomena.     

Nanoparticle with a ferrimagnetic interlayer coupling in the presence of single-ion anisotropis

The magnetic properties of a nanoparticle described by the transverse Ising model with single-ion anisotropis, which consists of a concentric spin-3/2 core and a hexagonal ring spin-5/2 shell coupled with a ferrimamagnetic interlayer coupling, are studied by the effective-field theory with self-spin correlations. Particular emphasis is given to the effects of the both the transverse field and the single-ion anisotropis on the longitudinal and transverse magnetizations, phase diagrams of the nanoparticle. We have found that, for appropriate values of the system parameters, one or two compensation points may be obtained in the present systems.     

Magnetic properties of a mixed spin-1 and spin-2 Heisenberg ferrimagnetic system: Green’s function study

The magnetic behaviors of a mixed spin-1 and spin-2 Heisenberg ferrimagnetic system on a square lattice are studied by using the double-time temperature-dependent Green’s function technique. In order to decouple the higher order Green’s functions, Anderson and Callen’s decoupling and random phase approximations have been used. The system is described in the presence of an external magnetic field. We illustrate the influences of the nearest- and next-nearest-neighbor interactions and the single-ion anisotropies with an external magnetic field on compensation and critical temperatures. We found that the system that includes only the nearest-neighbor interaction and the single-ion anisotropies does not have a compensation temperature. When the next-nearest-neighbor interactions exceed a certain minimum value, a compensation temperature begins to appear. For some negative values of single-ion anisotropies, there exist first-order phase transitions. The system has first-order phase transition properties when it is under the influence of an external magnetic field.     

Heat diffusion characteristics of magnetite nanoparticles dispersed hydro-gel in alternating magnetic field

Heat diffusion characteristics of a spherical heat source dispersing magnetite nanoparticles (MNPs) in hydro-gel were investigated numerically and experimentally to evaluate the conditions required for magnetic fluid hyperthermia (MFH). Numerical estimation assumed one-dimensional spherical model and constant heat evolution. Experimental observation was carried out by exposing the magnetite-dispersed hydro-gel in an AC magnetic field with strength and frequency of 3.2 kA/m and 600 kHz, respectively. The temperature distribution observed along the radial axis of the spherical heat source agreed well with the theoretical estimation quantitatively and qualitatively. However, the minor difference existed between the theory and experiment was due to the variation in experimentally determined and actual particle size distributions. Thus, we could conclude that the proposed algorithm could be extended to be used in the estimation of the temperature distribution in intravital conditions with blood flow, metabolism etc., to arrive at biologically significant conclusions helpful for MFH cancer treatment.     

Effect of poly (ethylene glycol) coating on the magnetic and thermal properties of biocompatible magnetic liquids

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.     

The analytical treatment of magnetic properties of three-layer ferrimagnetic superlattice

The Hamiltonian of the magnetic superlattice with three-layer unit cell was treated within the Boson formalism. The Boson Green’s functions (BGFs) were derived and it was shown that the system for BGFs splits into two sets which lead to the energies with opposite signs, although the energies of elementary excitations are strictly only the positive ones. However, when corresponding energies are used, the correlation functions calculated from both sets are the same. All the physically relevant quantities: total energy of the system, ground state energy, layer magnetization and zero-point (quantum) fluctuations are derived analytically by using both sets, showing that they lead to the same expressions. The Hamiltonian was also diagonalized by the so-called “u-v” transformation of the operators. It is shown that in spite of formal independence of the approaches, there exists a close relationship between BGF and “u-v” transformations.     

Structural analysis, magnetic and electrical properties of samarium substituted lithium-nickel mixed ferrites

A series of Sm-doped Li-Ni ferrites with formula of (Li_0.5Fe_0.5)_0.4Ni_0.6Sm_yFe_2−yO₄, where 0.0≤y≤0.1 were prepared by double sintering ceramic technique. The structure was characterized by X-ray diffraction, which has confirmed the formation of single-phase spinel structure. The samarium concentration dependence of lattice parameters obeys Vegard's law. The octahedral site radii increased with Sm content while the tetrahedral site radii decreased. Deviation from the ideal crystal structure (Δ) is found to decrease with Sm substitution, and the hopping length on the octahedral site is found to increase with Sm content. Hall measurement confirmed p-type conductivity behavior for Sm-doped ferrite and the main charge transport mechanism is hopping of halls between Ni²⁺ and Ni³⁺. Sintering at 1300 °C resulted in low resistivity ferrite, which was found to increase with Sm content. Resistivity is governed by both charge carrier mobility and carrier concentration. It decreases with frequency, and this behavior with frequency is discussed according to Koop's theorem. The dielectric constant is found to decrease more rapidly at low frequencies than at higher frequencies while the dielectric constant increases with Sm content. The decrease in ε″ with frequency agrees with Deby's type relaxation process. Maximum in ε″ is observed when the hopping frequency is equal to the external electric field frequency. The variation in tan δ with frequency shows a similar nature to that of ε″ with frequency. The magnetization under applied magnetic field for the samples exhibits a clear hysteretic behavior. The scanning electron microscope (SEM) studies showed that the domain walls may tend to be trapped (pinned) by non-magnetic inclusions, precipitates and voids. The saturation magnetization (M_S) increases with the sintering temperature, while the coercivity (H_Ci) is found to decrease.     

Large enhancement of domain wall-induced anomalous magnetoresistance in ferrimagnetic Tb/Co wires: The effect of injecting spin Hall current

We demonstrated domain wall (DW)-induced anomalous magnetoresistance (MR) generated in asymmetric and symmetric ferrimagnetic Tb/Co multilayered, and Tb–Co alloyed wires. The extraordinary Hall effect (EHE)-induced circulating currents in the vicinity of DWs between longitudinal voltage probes are assigned to the anomalous MR. A large anomalous MR ~1.5% was obtained in the asymmetric Tb/Co multilayered wire. The large MR can be attributed to an addition of spin Hall current with a long coherence length from an adjacent Pt layer. These results open new possibilities for the use of ferrimagnetic multilayered wires beyond multi-function devices.     

Synthesis of manganese oxide nanocrystal by ultrasonic bath: effect of external magnetic field

A novel technique was used for the synthesis of manganese oxide nanocrystal by applying an external magnetic field (EMF) on the precursor solution before sonication with ultrasonic bath. The results were compared in the presence and absence of EMF. Manganese acetate solution as precursor was circulated by a pump at constant speed (7 rpm, equal to flow rate of 51.5 mL/min) in an EMF with intensity of 0.38 T in two exposure times (t_MF, 2 h and 24 h). Then, the magnetized solution was irradiated indirectly by ultrasonic bath in basic and neutral media. One experiment was designed for the effect of oxygen atmosphere in the case of magnetic treated solution in neutral medium. The as prepared samples were characterized with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (HRTEM, TEM), energy-dispersive spectrum (EDS), and superconducting quantum interference device (SQUID) analysis. In neutral medium, the sonication of magnetized solution (t_MF, 24 h) led mainly to a mixture of Mn₃O₄ (hausmannite) and γ-MnOOH (manganite) and sonication of unmagnetized solution led to a pure Mn₃O₄. In point of particle size, the larger and smaller size of nanoparticles was obtained with and without magnetic treatment, respectively. In addition, the EMF was retarded the nucleation process, accelerated the growth of the crystal, and increased the amount of rod-like structure especially in oxygen atmosphere. In basic medium, a difference was observed on the composition of the products between magnetic treated and untreated solution. For these samples, the magnetic measurements as a function of temperature were exhibited a reduction in ferrimagnetic temperature to T_c = 39 K, and 40 K with and without magnetic treatment, respectively. The ferrimagnetic temperature was reported for the bulk at T_c = 43 K. A superparamagnetic behavior was observed at room temperature without any saturation magnetization and hysteresis in the measured field strength. The effect of EMF on the sample prepared in the basic medium was negligible but, in the case of neutral medium, the EMF affected the slope of the magnetization curves. The magnetization at room temperature was higher for the samples obtained in neutral medium without magnetic treatment. In addition, a horizontal shift loop was observed in neutral medium at low temperature.     

Magnetic properties and heating effect in bacterial magnetic nanoparticles

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.     

Large specific absorption rates in the magnetic hyperthermia properties of metallic iron nanocubes

We report on the magnetic hyperthermia properties of chemically synthesized ferromagnetic 11 and 16 nm Fe(0) nanoparticles of cubic shape displaying the saturation magnetization of bulk iron. The specific absorption rate measured on 16 nm nanocubes is 1690±160 W/g at 300 kHz and 66 mT. This corresponds to specific losses-per-cycle of 5.6 mJ/g, largely exceeding the ones reported in other systems. A way to quantify the degree of optimization of any system with respect to hyperthermia applications is proposed. Applied here, this method shows that our nanoparticles are not fully optimized, probably due to the strong influence of magnetic interactions on their magnetic response. Once protected from oxidation and further optimized, such nano-objects could constitute efficient magnetic cores for biomedical applications requiring very large heating power.     

Effect of the number of iron oxide nanoparticle layers on the magnetic properties of nanocomposite LbL assemblies

Aqueous colloidal suspension of iron oxide nanoparticles has been synthesized. Z-potential of iron oxide nanoparticles stabilized by citric acid was −35±3 mV. Iron oxide nanoparticles have been characterized by the light scattering method and transmission electron microscopy. The polyelectrolyte/iron oxide nanoparticle thin films with different numbers of iron oxide nanoparticle layers have been prepared on the surface of silicon substrates via the layer-by-layer assembly technique. The physical properties and chemical composition of nanocomposite thin films have been studied by atomic force microscopy, magnetic force microscopy, magnetization measurements, Raman spectroscopy. Using the analysis of experimental data it was established, that the magnetic properties of nanocomposite films depended on the number of iron oxide nanoparticle layers, the size of iron oxide nanoparticle aggregates, the distance between aggregates, and the chemical composition of iron oxide nanoparticles embedded into the nanocomposite films. The magnetic permeability of nanocomposite coatings has been calculated. The magnetic permeability values depend on the number of iron oxide nanoparticle layers in nanocomposite film.     

Investigations on structural and magnetic properties of cobalt ferrite/silica nanocomposites prepared by the coprecipitation method

Magnetic nanocomposites consisting of cobalt ferrite nanoparticles embedded in silica matrix were prepared by the coprecipitation method using metallic chlorides as precursors for ferrite. Subsequently composites were annealed at 100, 200 and 300 °C for 2 h. The samples were structurally characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The magnetic properties were measured in the temperature range of 10-300 K using vibrating sample magnetometer (VSM). The effects of thermal treatment on structural and magnetic properties of nanocomposites were investigated. When the samples were annealed, CoFe₂O₄ nanocrystallites were observed in the SiO₂ matrix, whose size increases with increase in annealing temperature. The coercivity and saturation magnetization of nanocomposite (annealed at 300 °C for 2 h) are much higher than that of bulk cobalt ferrite. The realization of adjustable particle sizes and controllable magnetic properties makes the applicability of the CoFe₂O₄ nanocomposite more versatile.     

Structural characterization and magnetic properties of superparamagnetic zinc ferrite nanoparticles synthesized by the coprecipitation method

Single phase zinc ferrite (ZnFe₂O₄) nanoparticles have been prepared by the coprecipitation method without any subsequent calcination. The effects of precipitation temperature in the range 20–80 °C on the structural and the magnetic properties of zinc ferrite nanoparticles were investigated. The crystallite size, microstructure and magnetic properties of the prepared nanoparticles were studied using X-ray diffraction (XRD), Fourier transmission infrared spectrum, transmission electron microscope (TEM), energy dispersive X-ray spectrometer and vibrating sample magnetometer. The XRD results showed that the coprecipitated nanoparticles were single phase zinc ferrite with mixture of normal and inverse spinel structures. Furthermore, ZnFe₂O₄ nanoparticles have the crystallite size in the range 5–10 nm, as confirmed by TEM. The magnetic measurements exhibited that the zinc ferrite nanoparticles synthesized at 40 °C were superparamagnetic with the maximum magnetization of 7.3 emu/g at 10 kOe.     

Pressure effect on the magnetic properties of CeSb

Changes in the magnetic field-temperature phase diagram of CeSb with pressure have been determined up to 6kbar by magnetization measurements on a single crystal. High magnetic fields up to 70 kOe have been applied along a four fold axis of the rock-salt type structure. The features of the phase diagram are not changed by pressure except for a shift towards high temperature. The saturated magnetic moment and the hysteresis of the transition fields are independent of pressure. Variation of exchange energy with volume is deduced from the experimental results. It is shown that the effect of pressure and the magnetic volume anomaly at 0 K are essentially due to the variation of the exchange energy in the ferromagnetic (001) planes.     

Tuning magnetic properties of magnetoelectric BiFeO3-NiFe2O4 nanostructures

Multifunctional thin film nanostructures containing soft magnetic materials such as nickel ferrite are interesting for potential applications in microwave signal processing because of the possibility to shrink the size of device architecture and limit device power consumption. An essential prerequisite to future applications of such a system is a firm understanding of its magnetic properties. We show that nanostructures composed of ferrimagnetic NiFe₂O₄ pillars in a multiferroic BiFeO₃ matrix can be tuned magnetically by altering the aspect ratio of the pillars by depositing films of varying thickness. Magnetic anisotropy is studied using ferromagnetic resonance, which shows that the uniaxial magnetic anisotropy in the growth direction changes sign upon increasing the film thickness. The magnitude of this anisotropy contribution can be explained via a combination of shape and magnetostatic effects, using the object-oriented micromagnetic framework (OOMMF). The key factors determining the magnetic properties of the films are shown to be the aspect ratio of individual pillars and magnetostatic interactions between neighboring pillars.