Effect of Zn substitution on the AC induction heating properties of ZnxMn1-xFe2O4 (x = 0.1–0.9) nanoparticles prepared using microwave assisted synthesis

Zn_xMn_1-xFe₂O₄ (x = 0.1–0.9) magnetic nanoparticles (MNPs) were prepared using a microwave-assisted coprecipitation method, and the effect of Zn substitution on the AC induction heating properties of the MNPs was investigated. With increasing Zn substitution, owing to the lower solubility product of Zn²⁺ ions, the formation of new nuclei was preferred over grain growth, which reduced the average crystallite size. The saturation magnetization initially increased with Zn substitution, attained the maximum value at x = 0.5, and decreased beyond that due to Yafet-Kittel type triangular spin ordering. The prepared MNPs exhibited superparamagnetic behaviour at ～ 300 K. AC induction heating studies of the MNPs indicated a specific absorption rate of ～ 130 ± 4 W/g_Fe at x = 0.1. The AC induction heating efficiency did not exhibit any non-monotonic variation at x = 0.5, and progressively decreased with increasing Zn concentration. This was attributed to the reduction in the MNP size and anisotropy energy density at higher Zn concentration that caused the relaxation dynamics to be Nèel dominated with lower effective relaxation time. AC induction heating studies on the agar-immobilized samples confirmed the Brownian relaxation mediated magneto-thermal energy conversion at lower Zn concentration. The obtained results demonstrated that saturation magnetization alone does not influence the AC induction heating efficiency and relaxation dynamics play a significant role.     

Synthesis and magneto-structural properties of chitosan coated ultrafine cobalt ferrite nanoparticles for magnetic fluid hyperthermia in viscous medium

AC induction heating mediated magnetic fluid hyperthermia of superparamagnetic nanoparticles (MNPs) is being widely explored for localized thermo-therapy of tumours. One of the primary hindrances for rapid adaptation of this technique is the loss of heating efficiency when the MNPs are placed within the viscous tissue medium, which necessitates undesired increase in MNP concentrations or exposure time during practical applications. With an objective to mitigate this, here we report the viscosity independent magnetic hyperthermia properties of biocompatible ultrafine (average size ～ 2.5 nm) chitosan-coated superparamagnetic CoFe₂O₄ MNPs synthesized using a low-cost co-precipitation technique. The presence of the chitosan coating is confirmed from Fourier transform infrared and X-ray photoelectron spectroscopy. The superparamagnetic nature of the synthesized MNPs at 300 K is confirmed from Mössbauer spectroscopy, isothermal and temperature dependent magnetization studies. Experimental findings indicate a higher field-induced heating efficiency for the chitosan-coated MNPs due to superior colloidal stability. The ultrafine size, combined with higher anisotropy energy density, results in viscosity independent Nèel relaxation-dominated magneto-thermal energy conversion for the CoFe₂O₄ MNPs. Experimental results reveal negligible loss of heating efficiency due to partial abrogation of Brownian relaxation when the chitosan-coated MNPs are immobilized in a tissue-equivalent agar medium, which is beneficial for practical applications. The heating efficiency of ～72.1 ± 2.8 W/g_Fe (at 33.1 kA/m and 126 kHz), obtained in the present study for the chitosan-coated MNPs, is higher than the previously documented values for ultrafine CoFe₂O₄ MNPs, which is useful for reducing the exposure time during practical applications. Further, the chitosan coating rendered the ultrafine CoFe₂O₄ MNPs bio-compatible against L929 cell line. The satisfactory magnetic fluid hyperthermia efficiency, negligible room temperature coercivity, retention of the field-induced heating efficiency in tissue-equivalent agar medium due to Nèel-dominated relaxation dynamics and superior biocompatibility, make the chitosan-coated ultrafine CoFe₂O₄ MNPs an attractive candidate for practical MFH applications.     

Preparation,physicochemical characterization,and AC induction heating properties of colloidal aggregates of ferrimagnetic cobalt ferrite nanoparticles coated with a bio-compatible polymer

AC induction heating properties of colloidal nano-aggregates of ferrimagnetic cobalt ferrite magnetic nanoparticles (MNPs) are reported in this study. Bio-compatible chitosan polymer-coated CoFe₂O₄ MNPs are synthesized using a co-precipitation method. Powder X-ray diffraction indicates the formation of mixed spinel structures for the uncoated (CP) and chitosan-coated (CP–CHN) MNPs, which is also supported by the cation distributions obtained from the Mössbauer spectra. The presence of chitosan coating on the surface of the CP-CHN MNPs is confirmed using X-ray photoelectron and Fourier transform infrared spectroscopy studies. Transmission electron microscopy shows primary particle sizes of ∼13 nm, which is larger than the superparamagnetic size limit of the CoFe₂O₄ MNPs. Hence, the CP and CP-CHN MNPs exhibit ferrimagnetic behaviour at room temperature with estimated saturation magnetization values of ∼77.4 emu/g and ∼74.4 emu/g, respectively. The average hydrodynamic diameter is found to be ∼90 ± 8 nm for an aqueous dispersion of the CP-CHN MNPs, which indicate the formation of colloidal nano-aggregates due to the ferrimagnetic interaction of the primary MNPs. The CP-CHN sample exhibits a significantly high AC induction heating efficiency of ∼267.2 ± 4.0 W/g_Fe, where the higher heating efficiency is attributed to the combination of hysteresis and relaxation-mediated magneto-thermal energy conversion, as confirmed using Stoner-Wohlfarth model-based dynamic hysteresis loop calculations. Further, the heating efficiency decreases with increasing sample concentration due to an increase in dipolar interaction, which is confirmed using semi-empirical calculations, where a lowering of the initial susceptibility is observed at higher concentrations. The higher AC induction heating efficiency, coupled with the demonstrated significant bio-compatibility during in vitro cytotoxicity studies, make the cobalt ferrite nano-aggregates potential candidates for magnetic hyperthermia.     

Preparation of Y3Fe5O12 Microsphere Using Bead‐Milled Nanosize Powder for Embolization Therapy Application

Y₃Fe₅O₁₂ microspheres having a 20–32 μm diameter range were prepared by a spray dryer using a bead‐milled nanosize powder. The high heat generation ability in an AC magnetic field was obtained by the bead milling of a commercial powder. The yield of the 20–32 μm microspheres was 13.5% after sifting using 20 and 32 μm sieves. The heat generation ability of the microsphere sample was almost the same as that for the bead‐milled powder because the temperature enhancement mechanism was the Néel relaxation of the superparamagnetic material. Furthermore, the heat generation ability of the Y₃Fe₅O₁₂ microsphere was improved by calcination at low temperature. The heat ability increased as a function proportional to the square of the increasing magnetic field for the noncalcined sample and the samples calcined at 600°C. For the samples calcined at 650°C or higher, the heat generation ability increased as a function proportional to the cube of the increasing magnetic field because of the particle growth to form single‐domain ferrimagnetic particles. The sample calcined at 650°C showed the maximum heat generation ability(W/g) of 2.4·f·H³, where f and H are the frequency (kHz) and magnetic field (kA/m), respectively.     

Single-phase and binary phase nanogranular ferrites for magnetic hyperthermia application

The study demonstrates the performance of heating efficiency in single-phase and binary phase spinel ferrite nanosystems. Ferrimagnetic cobalt ferrite (CoFe₂O₄) (CFO) and superparamagnetic copper ferrite/copper oxide (CuFe₂O₄/CuO) (CuF) nanosystems of different particle sizes were synthesized through a microwave-assisted coprecipitation method. The heating behavior was observed in range of both field amplitudes (8-24 kA/m at 516 kHz) and frequencies (325-973 kHz at 12 kA/m). The heating efficiency was analyzed and compared by means of particle size, magnetization, effective anisotropy constant, and Néel relaxation mechanism. Indeed, the heating rate was maximized in larger ferrite particles with low effective anisotropy constant. Moreover, though the magnetization and effective anisotropy constant of single-phase CoFe₂O₄ nanoparticles were higher, the binary phase CuFe₂O₄/CuO nanosystems of similar crystallite size (28 nm) exhibited superior heating efficiency (4.21°C/s). For a field amplitude and frequency of 24 kA/m and 516 kHz, the heating rate of CuF and CFO ferrites with different crystallite sizes decreased in the order of 4.21 > 2.14 > 0.58 > 0.52°C/s for 29 nm > 25 nm > 12 nm > 15 nm, respectively. The results emphasize that binary phase ferrite nanoparticles are better thermoseeds than the single-phase ferrites for the magnetic hyperthermia application.     

Field Dependence of the Spin Relaxation Within a Film of Iron Oxide Nanocrystals Formed via Electrophoretic Deposition

The thermal relaxation of macrospins in a strongly interacting thin film of spinel-phase iron oxide nanocrystals (NCs) is probed by vibrating sample magnetometry (VSM). Thin films are fabricated by depositing FeO/Fe₃O₄ core–shell NCs by electrophoretic deposition (EPD), followed by sintering at 400°C. Sintering transforms the core–shell structure to a uniform spinel phase, which effectively increases the magnetic moment per NC. Atomic force microscopy (AFM) confirms a large packing density and a reduced inter-particle separation in comparison with colloidal assemblies. At an applied field of 25 Oe, the superparamagnetic blocking temperature is T _B^SP ≈ 348 K, which is much larger than the Néel-Brown approximation of T _B^SP ≈ 210 K. The enhanced value of T _B^SP is attributed to strong dipole–dipole interactions and local exchange coupling between NCs. The field dependence of the blocking temperature, T _B^SP(H), is characterized by a monotonically decreasing function, which is in agreement with recent theoretical models of interacting macrospins.     

Thermal Expansion of Alkaline‐Doped Lanthanum Ferrite Near the Néel Temperature

The thermal expansion and magnetic behaviors of divalent, alkaline‐doped lanthanum ferrites (La_0.9M_0.1FeO₃, M=Ca, Sr, Ba) were assessed using a combination of dilatometry, magnetometry, time‐of‐flight neutron diffraction, and high‐temperature X‐ray diffraction. Néel temperatures were determined through vibrating sample magnetometry and correlated well with changes in thermal expansion behavior observed during both dilatometry and X‐ray diffraction. The Néel temperatures observed for pure, Ca‐doped, Sr‐doped, and Ba‐doped lanthanum ferrites were 471°C, 351°C, 465°C, and 466°C, respectively. The effect of divalent substitutions on the magnetic behavior are attributed to charge compensation mechanisms and structural changes in the material.     

Dielectric and Magnetic Properties of Sr(Fe1/2Ta1/2)O3 Complex Perovskite Ceramics

The dielectric and magnetic properties of Sr(Fe_1/2Ta_1/2)O₃ complex perovskite ceramics were systematically investigated together with the structure. The X‐ray powder diffraction analysis confirmed a B‐site disordered orthorhombic structure in space group Pbnm. Only one broadened dielectric peak with strong frequency dispersion was observed in the present ceramics, which was significantly different from that for the analogue Ba(Fe_1/2Nb_1/2)O₃ and Ba(Fe_1/2Ta_1/2)O₃. The strong dependence of sample thickness and electrode material indicated that the dielectric relaxation behavior at lower frequency was due to the interface effects. The present ceramics were spin glass state with slight ferromagnetic behavior below the Néel temperature (20 K). The co‐presence of Fe³⁺ and Fe²⁺ was confirmed by the μ_eff value.     

Tuning specific loss power of CoFe2O4 nanoparticles by changing surfactant concentration in a combined co-precipitation and thermal decomposition method

New synthetic approaches of nanoparticles (NPs) can be used for magnetic hyperthermia, destroying malignant cells without damaging healthy tissues. Here, a combination of co-precipitation and thermal decomposition techniques was employed to synthesize monodisperse CoFe₂O₄ NPs. A mixture of oleylamine and oleic acid with different concentrations was utilized as a surfactant, significantly changing magnetic, morphological and structural properties of the NPs. Increasing the surfactant concentration from 1 to 7.5 mmol resulted in maximum and minimum coercivity and saturation magnetization of 420.0 Oe 73.6 emu/g, and 67.2 Oe and 48.3 emu/g, respectively, arising from the prevention of agglomeration and reduction in crystallite size. The first-order reversal curve analysis was employed to clarify the role of the surfactant in magnetic distributions and detailed characteristics. The specific loss power of the NPs was found to be tuned for the different surfactant concentrations, achieving a maximum of 268.5 W/g at 7.5 mmol for CoFe₂O₄ NPs with enhanced superparamagnetic contribution in Néel and Brownian mechanisms. MTT assay of the NPs was also carried out, indicating their low cytotoxicity.     

Transmittance Measurements in Non-alternating Magnetic Field as Reliable Method for Determining of Heating Properties of Phosphate and Phosphonate Coated Fe3O4 Magnetic Nanoparticles

Different phosphates and phosphonates have shown excellent coating ability toward magnetic nanoparticles, improving their stability and biocompatibility which enables their biomedical application. The magnetic hyperthermia efficiency of phosphates (IDP and IHP) and phosphonates (MDP and HEDP) coated Fe₃O₄ magnetic nanoparticles (MNPs) were evaluated in an alternating magnetic field. For a deeper understanding of hyperthermia, the behavior of investigated MNPs in the non-alternating magnetic field was monitored by measuring the transparency of the sample. To investigate their theranostic potential coated Fe₃O₄-MNPs were radiolabeled with radionuclide ¹⁷⁷Lu. Phosphate coated MNPs were radiolabeled in high radiolabeling yield (>?99%) while phosphonate coated MNPs reached maximum radiolabeling yield of 78%. Regardless lower radiolabeling yield both radiolabeled phosphonate MNPs may be further purified reaching radiochemical purity of more than 95%. In vitro stabile radiolabeled nanoparticles in saline and HSA were obtained. The high heating ability of phosphates and phosphonates coated MNPs as sine qua non for efficient in vivo hyperthermia treatment and satisfactory radiolabeling yield justifies their further research in order to develop new theranostic agents.

     

Solution combustion synthesis of new metal borophosphates (Fe1-xCrx)2B(PO4)3: Structural,thermal, surface,and magnetic properties

The new borophosphates were successfully synthesized by solution combustion synthesis assisted with glycine. The obtained materials were systematically characterized by Fourier-transform infrared spectroscopy, X-ray powder diffraction, UV–visible spectroscopy, thermogravimetric analysis, scanning electron microscopy, Brauner-Emmett-Teller surface area, and magnetometry. The Rietveld refinements indicated that Fe₂B(PO₄)₃ is a hexagonal, space group P63/m with a = b = 8.029 and c = 7.408. As Cr substitutes the Fe atoms, there is a significant decrease in the lattice parameters. When all Fe atoms are replaced by Cr, Cr₂B(PO₄)₃ is formed and the structure turns out to be a trigonal, space group P3 with a = b = 7.950 and c = 7.360. The materials are thermally stable and demonstrate paramagnetic behavior at room temperature. The magnetization increases as the iron content increases because of the high magnetic moment of the iron ion. Temperature-dependent magnetic measurements reveal that Fe₂B(PO₄)₃ has a Néel transition at 30 K and the Néel temperature decreases with Cr substitution.     

Preparation,Dielectric, and Magnetic Characteristics of LuFe2O4 Ceramics

Preparation of LuFe₂O₄ ceramics under vacuum environment was investigated together with the structural, dielectric, and magnetic characterization. Single‐phase LuFe₂O₄ could be obtained by the present process and the crystal structure was identified to be rhombohedral in space group . An obvious dielectric relaxation with activation energy of 0.29 eV was observed between 175 and 275 K. The Néel temperature of the present ceramics was ~250 K, and a reentrant spin glass transition was indicated at ~216 K. Two anomalies were observed in the DSC curve, which were relative with the ferrimagnetic transition and 2D–3D charge ordering transition of LuFe₂O₄. Meanwhile, a remarkable decrease appeared in the dielectric constant of the as‐magnetized LuFe₂O₄ sample, implying the magnetodielectric effect in the present ceramics.     

Magnetic properties of Co3O4 polycrystal powder

The results of investigations of magnetic properties of Co₃O₄ polycrystals in powder morphology with average crystallite size of 10 µm are presented. The temperature dependence of the magnetic susceptibility, measured in a wide temperature interval (1.5≤T≤400 K) using SQUID magnetometer, as well as electron spin resonance (ESR) spectra measured at X-band and Q-band frequency ranges have been studied. Antiferromagnetism with a Néel temperature T_N at about 39 K was observed from the analysis of evolution of molar magnetic susceptibility and ESR intensity as a function of temperature. ESR parameters namely g-factor, intensity (I_ESR), g-value, and linewidth ΔH for powder Co₃O₄ have been obtained. Some deviations from the expected values of some magnetic properties were determined and discussed.     

“One‐pot” synthesis of well‐defined functional copolymer and its application as tumor‐targeting nanocarrier in drug delivery

A one‐pot synthesis is developed for PEG₆₀₀‐b‐poly(glycerol monoacrylate) (PEG₆₀₀‐b‐PGA), by which folate and superparamagnetic iron oxide nanoparticles (SPIONs) are assembled to form folic acid‐conjugated magnetic nanoparticles (FA‐MNPs) as a tumor targeting system. The synthesis consists of a “click” reaction and atom transfer radical polymerization (ATRP) to obtain the well‐defined furan‐protected maleimido‐terminated PEG₆₀₀‐b‐poly(solketal acrylate) (PEG₆₀₀‐b‐PSA) copolymer. After deprotection, the key copolymer N‐maleimido‐terminated PEG₆₀₀‐b‐PGA is successfully conjugated with thiol derivatives of folate and FITC, respectively. FA‐MNPs are developed by assembling of the resulting polymer FA‐PEG₆₀₀‐b‐PGA with SPIONs, and characterized for their size, surface charge, and superparamagnetic properties. To investigate the cellular uptake of the nanoparticles by Hela cells and φ2 cells using fluoresce technique, FA‐FITC‐MNPs are also obtained by assembling of FA‐PEG₆₀₀‐b‐PGA, FITC‐PEG₆₀₀‐b‐PGA with SPIONs. Qualitative and quantitative determinations of FA‐FITC‐MNPs show that the particles specifically internalized to Hela cells. No significant cytotoxicity is observed for these two kinds of cell lines. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40405.     

Structural and magnetic properties of LaCrO3 half-doped with Al

Structural and magnetic properties of LaCrO₃ half-doped with Al are reported in this work. Pure and half-doped samples were prepared by combustion synthesis using urea as fuel. The crystal structure was investigated by X-ray diffraction and Rietveld analysis. A structural phase transition caused by a decrease of the chemical pressure was observed. The scanning electron microscopy (SEM) images show the formation of porous samples with particles of irregular morphologies. A quantitative Energy-dispersive X-ray spectroscopy (EDS) analysis on the surface indicates the inclusion of the Al on the structure. However, a small deficiency of La and Al was observed. Magnetization measurements as a function of temperature reveal an antiferromagnetic order in both samples. A large decrease of T_N (Néel temperature) and a reduction of the frustration factor is observed in the sample doped with Al. The magnetic isothermal at 5 K shows a typical antiferromagnetic behavior with a slightly spin canting for the doped sample.     

Entrapment of enzyme-linked magnetic nanoparticles within poly(ethylene glycol) hydrogel microparticles prepared by photopatterning

In this study, hydrogel microparticles containing enzyme-linked magnetic nanoparticles (MNPs) were prepared. Peroxidase (POD), a model enzyme, was covalently immobilized on the surface of MNPs using 3-aminopropyltriethoxysilane (APTES), and the resultant POD-linked MNPs were entrapped within various shapes of hydrogel microparticles using photopatterning. Pre-immobilizing POD on the MNP surface made it possible to use hydrogels prepared from high molecular weight PEG without enzyme leaching, which enhanced the reaction rate of entrapped enzymes by reducing resistance to mass transport. Quantitative assays showed a linear correspondence between fluorescence intensity and H₂O₂ concentrations below 15 mM.     

Influence of iron oxide substitution on the magnetic interactions in sol–gel-derived 45S5 bioactive glass–ceramics

Magnetic interactions in sol–gel-derived bioactive magnetic glass–ceramics (MGCs) with compositions of (45 − x)SiO₂·24.5CaO·24.5Na₂O·6P₂O₅ xFe₂O₃ (2 ≤ x ≥ 15 wt.%) have been investigated using electron paramagnetic resonance (EPR), and temperature-dependent magnetic susceptibility and magnetization (M–T) techniques. EPR spectra of the MGC samples revealed strong composition dependence in the intensity and linewidth of resonance absorptions at g ≈ 2.0 and g ≈ 4.3. EPR linewidth analysis showed the dominance of dipole–dipole interaction in MGC samples with iron oxide content ≤4 wt.% and a crossover to super-exchange type interaction in samples with higher iron oxide content. Composition-dependent magnetic interaction in these MGC could be related to Fe²⁺ and Fe³⁺ ion concentrations using high-temperature magnetic susceptibility studies. Zero-field cooled and field cooled M–T curves indicate different magnetic behavior for MGC samples with x ≤ 6 and x ≥ 8 wt.% iron oxide. Although the former show weak magnetic behavior, the latter exhibit superparamagnetic behavior which could be correlated with the percentage of magnetic phases present in each sample. These studies reveal composition-dependent variation in dipolar and super-exchange type interaction in the samples which could help in assessing these MGC for biomedical applications.     

Crystal structure and multiferroic behavior of perovskite YFeO3

We present a study of multiferroic properties of YFeO₃ synthesized by means of high-energy ball milling assisted by annealing at low temperature. Fe₂O₃ and Y₂O₃ powders were mixed in a stoichiometric ratio, milled for 5?h, pressed and annealed at temperature from 773 to 1073?K. X-ray diffraction (XRD) analysis confirmed the formation of single-phase orthorhombic structure. Magnetic hysteresis loops, at room temperature, from vibrating sample magnetometry show the transition from ferromagnetic order to G-antiferromagnetic order, related to the transformation from amorphous to crystalline orthorhombic single phase. The value of Néel temperature of single phase YFeO₃ was obtained at 595?K, lower than previously reported. Dielectric behavior at room temperature of YFeO₃ single-phase sample shows a direct dependence with frequency of both dielectric constant and dielectric loss, in good agreement with Maxwell-Wagner effect. A fit made using Cole-Cole equation shows that the Low Temperature Dielectric Relaxation, LTDR, corresponds to a Debye-type relaxation. Finally, it was found that AC conductivity (σ_AC) increases linearly with frequency. All results show that YFeO₃ synthesized by high-energy ball milling assisted with annealing possess a multiferroic behavior.     

Superparamagnetic Hyperthermia Study with Cobalt Ferrite Nanoparticles Covered with γ-Cyclodextrins by Computer Simulation for Application in Alternative Cancer Therapy

In this paper, we present a study by computer simulation on superparamagnetic hyperthermia with CoFe₂O₄ ferrimagnetic nanoparticles coated with biocompatible gamma-cyclodextrins (γ-CDs) to be used in alternative cancer therapy with increased efficacy and non-toxicity. The specific loss power that leads to the heating of nanoparticles in superparamagnetic hyperthermia using CoFe₂O₄–γ-CDs was analyzed in detail depending on the size of the nanoparticles, the thickness of the γ-CDs layer on the nanoparticle surface, the amplitude and frequency of the alternating magnetic field, and the packing fraction of nanoparticles, in order to find the proper conditions in which the specific loss power is maximal. We found that the maximum specific loss power was determined by the Brown magnetic relaxation processes, and the maximum power obtained was significantly higher than that which would be obtained by the Néel relaxation processes under the same conditions. Moreover, increasing the amplitude of the magnetic field led to a significant decrease in the optimal diameter at which the maximum specific loss power is obtained (e.g., for 500 kHz frequency the optimal diameter decreased from 13.6 nm to 9.8 nm when the field increased from 10 kA/m to 50 kA/m), constituting a major advantage in magnetic hyperthermia for its optimization, in contrast to the known results in the absence of cyclodextrins from the surface of immobilized nanoparticles of CoFe₂O₄, where the optimal diameter remained practically unchanged at ~6.2 nm.     

The zero-field magnetic ground state of EuC6 investigated by muon spectroscopy

The magnetic ground state of EuC₆, a first-stage graphite intercalation compound, was investigated by means of zero-field muon spectroscopy. Below the Néel antiferromagnetic temperature (42 K), the highly damped oscillations in the muon asymmetry could be modelled with a Bessel line shape, indicative of an incommensurate magnetic order. The internal magnetic field, as probed by the implanted muons, lies in the plane of the europium ions, has an average intensity of 150(22) mT, and seems to arise from a strong contact hyperfine interaction. The latter partially cancels out the dipolar contribution to the local field, in turn due to the localized Eu spins arranged in an antiferromagnetic triangular lattice (frustrated spin lattice) with negligible inter-layer couplings.