Superparamagnetic-like Behavior Research Articles

Spectroscopic analysis of nanosized Zn(Ag, Ni)O systems and observation of superparamagnetism at low temperature.

To understand the impact of binary doping in ZnO, nanosized Zn(Ag, Ni)O systems were synthesized by the sol-gel method. The amount of Ag was fixed at 2 at%, and that of Ni was varied from 1 to 15 at%. Ni incorporation equal to or beyond 3 at% gave rise to the development of the NiO phase. The presence of Ag and Ni did not have much influence on the lattice constants of ZnO. However, a larger addition of Ni impacted the unit cell of NiO, as indicated by the reduction of the lattice constant of NiO. The increase in NiO and Ag contents in ZnO reduced the second and third harmonic intensities under non-linear investigations. X-ray photoelectron spectroscopy analysis indicated that initial Ni addition varied randomly along with Ag, and it stabilized itself at higher concentration. Field emission scanning electron microscopy revealed that interlinked particles and chains with tamarind shapes were formed, closely matching the rod-like structures under high resolution. Ag and Ni addition altered the structures slightly and randomly till 5 at% Ni; thereafter they deviated from the particle shape to flat disc-shapes. Interestingly, the magnetic response of the sample was determined by the NiO phase, and the effect of Ni and Ag substitution in the ZnO host matrix was almost irrelevant at low temperatures toward magnetic contribution. Weak ferromagnetism at low temperatures (≤50 K) with superparamagnetic-like behavior (cusp in ZFC magnetization) was observed in all the samples. This could be attributed to the finite nano-size effect and uncompensated spins at the surface of the particle.

Effect of Ca2+ doping and annealing temperature on the structure, morphology and magnetic behavior of CaxCo1-xFe2O4/SiO2 nanocomposites

Co-doped ferrites are promising functional materials for many practical applications and their physical properties can be tailored by changing their composition. This study assesses the structure, morphology and magnetic properties of CaxCo1-xFe2O4/SiO2 (x = 0.0–0.5) nanocomposites (NCs) obtained by sol–gel method and annealed at different temperatures (400, 800 and 1200 °C). The effect of Ca2+ doping on the properties of nano-structured Ca-Co ferrite embedded in the SiO2 matrix was investigated by thermogravimetry and differential thermal analysis, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy, Brunauer-Emmett-Teller surface area, inductively coupled plasma optical emission spectrometry, atomic force microscopy (AFM) and magnetic measurements. The thermal analysis showed the formation of metal succinates up to 200 °C and of ferrite above 280 °C. The presence of poorly crystalline ferrite accompanied by silicates at low annealing temperatures and of highly crystalline ferrite accompanied by SiO2 and Ca silicates at high annealing temperatures was identified by XRD. The increased Ca2+ doping led to a decrease in the structural parameters estimated by XRD and the surface area. The AFM images revealed that the NCs have a crystalline core covered by a layer of amorphous SiO2. The hysteresis loop shape indicated the superparamagnetic-like and ferromagnetic behavior of the obtained NCs. The magnetic properties improved with the increase in annealing temperature and depended on the particle size and dopant content. The NCs with low Ca2+ content annealed at 800 °C still show appreciable hysteresis, but doping with high Ca2+ contents drastically affects the magnetic properties.

Influence of Ni2+ substitution by Co2+ on the morphology and magnetic properties of single domain CoαNi0.9-αZn0.1Fe2O4 nanoparticles

This study presents the effect of Ni2+ substitution by Co2+ on the structure, morphology and magnetic properties of CoαNi0.9-αZn0.1Fe2O4 nanoparticles calcined at different temperatures. Fourier-transform infrared spectroscopy revealed the presence of Fe-O, Co-O, Zn-O and Ni-O bonds in samples calcined at 200 °C, while the presence of the characteristic bonds of the SiO2 confirmed the embedding of CoαNi0.9-αZn0.1Fe2O4 at all calcination temperatures. Single phase poorly crystalline ferrite for samples calcined at 400 °C and ferrite accompanied by traces of Fe2SiO4 and SiO2 for samples calcined at high temperatures (800 and 1200 °C) were identified. The dependence of X-ray diffraction parameters on the Co2+ content of nanoparticles was also investigated. The increase in Co2+ content and calcination temperature led to crystallite growth from 4 to 43 nm, while the porosity decreased with the increase in Co2+ content and calcination temperature. The magnetic properties of the rectangular shape nanoparticles evolved proportionally with the particle size. The magnetization, coercivity and magnetocrystalline anisotropy increased with the increase in Co2+ content and calcination temperature. The shape of hysteresis loops indicated a superparamagnetic-like behavior of the nanoparticles calcined at 400 °C and a ferrimagnetic-like behavior at higher calcination temperatures (800 and 1200 °C). These features make the obtained nanoparticles attractive candidates for various technical applications.

Superparamagnetic-like Micrometric Single Crystalline Magnetite for Biomedical Application Synthesis and Characterization

Single-crystalline magnetite (Fe3O4) particles having a size beyond the nanometric range (1 µm to 50 µm) and showing high (close to the bulk value) saturation-specific magnetization (σs = 92 emu/g), were obtained by the hydrothermal decomposition of the Fe-EDTA complex. The very low values of the magnetic remanence (σr = 0.82 emu/g) and coercitivity (μoHc = 1.53 mT) observed at room temperature (RT) suggest a superparamagnetic-like behavior, which is quite remarkable for such micrometric magnetite particles. As confirmed by vibrating sample magnetometer (VSM)-based measurements, minor changes in their magnetic properties occur between RT and 5K. Scanning electron microscopy (SEM) has revealed a morphology consisting of a combination of non-porous octahedral- and dodecahedral-shaped particles, energy dispersive X-ray analysis (EDX) has indicated high elemental (Fe and O) purity, whereas X-ray diffraction (XRD) has confirmed a single crystal structure. The nitrogen adsorbtion–desorption isotherm and pore size distribution are presented for the magnetite sample. Thermomagnetic records under zero field-cooled (ZFC) and field-cooled (FC) conditions have revealed a thermal hysteresis of the Verwey transition.The Verwey point (TV) at which the major step of the phase transformation takes place is located around 132 K for heating and around 122 K for cooling. These microcrystals do not remain agglomerated when the polarizing field is removed, an essential requirement in biomedical applications is met.

High efficiency of magnetite nanoparticles for the arsenic removal from an aqueous solution and natural water taken from Tambo River in Peru.

Water is an essential compound on earth and necessary for life. The presence of highly toxic contaminants such as arsenic and others, in many cases, represents one of the biggest problems facing the earth´s population. Treatment of contaminated water with magnetite (Fe3O4) nanoparticles (NPs) can play a crucial role in arsenic removal. In this report, we demonstrate arsenic removal from an aqueous solution and natural water taken from the Peruvian river (Tambo River in Arequipa, Peru) using magnetite NPs synthesized by the coprecipitation method. XRD data analysis of Fe3O4 NPs revealed the formation of the cubic-spinel phase of magnetite with an average crystallite size of ~ 13nm, which is found in good agreement with the physical size assessed from TEM image analysis. Magnetic results evidence that our NPs show a superparamagnetic-like behavior with a thermal relaxation of magnetic moments mediated by strong particle-particle interactions. FTIR absorption band shows the interactions between arsenate anions and Fe-O and Fe-OH groups through a complex mechanism. The experimental results showed that arsenic adsorption is fast during the first 10min; while the equilibrium is reached within 60min, providing an arsenic removal efficiency of ~ 97%. Adsorption kinetics is well modeled using the pseudo-second-order kinetic equation, suggesting that the adsorption process is related to the chemisorption model. According to Langmuir's model, the maximum arsenic adsorption capacity of 81.04mg·g- 1 at pH = 2.5 was estimated, which describes the adsorption process as being monolayer, However, our results suggest that multilayer adsorption can be produced after monolayer saturation in agreement with the Freundlich model. This finding was corroborated by the Sips model, which showed a good correlation to the experimental data. Tests using natural water taken from Tambo River indicate a significant reduction of arsenic concentration from 356µg L- 1 to 7.38µg L- 1, the latter is below the limit imposed by World Health Organization (10µg L- 1), suggesting that magnetite NPs show great potential for the arsenic removal.

Dependence of Structural, Morphological and Magnetic Properties of Manganese Ferrite on Ni-Mn Substitution.

This paper presents the influence of Mn2+ substitution by Ni2+ on the structural, morphological and magnetic properties of Mn1−xNixFe2O4@SiO2 (x = 0, 0.25, 0.50, 0.75, 1.00) nanocomposites (NCs) obtained by a modified sol-gel method. The Fourier transform infrared spectra confirm the formation of a SiO2 matrix and ferrite, while the X-ray diffraction patterns show the presence of poorly crystalline ferrite at low annealing temperatures and highly crystalline mixed cubic spinel ferrite accompanied by secondary phases at high annealing temperatures. The lattice parameters gradually decrease, while the crystallite size, volume, and X-ray density of Mn1−xNixFe2O4@SiO2 NCs increase with increasing Ni content and follow Vegard’s law. The saturation magnetization, remanent magnetization, squareness, magnetic moment per formula unit, and anisotropy constant increase, while the coercivity decreases with increasing Ni content. These parameters are larger for the samples with the same chemical formula, annealed at higher temperatures. The NCs with high Ni content show superparamagnetic-like behavior, while the NCs with high Mn content display paramagnetic behavior.

Assessment of magnetic properties and structural evolution of nanostructured (Fe30Cu70)96B4 alloys

(Fe30Cu70)96B4 (FCB) alloys were produced in an induction furnace and then reduced in size by mechanical milling in stainless steel vials in an Ar atmosphere. Structural, morphological, and magnetic characterization techniques were used to investigate the evolution of powder alloys as a function of their milling time (0, 12, 24, 36, 48, and 60 h). Structural analysis by X-ray diffraction confirmed that all samples exhibit a crystalline fcc structure and space group Fm-3 m. As the milling time increases, the induced stress increments, leading to changes in the lattice parameter value and atomic volume. Thus, lattice parameter values are approximately in the range a = 0. 3614–0.3626 nm. TEM analysis confirmed that after 12 h of milling, the FCB system was made up of nanoparticles with diameters between 6 and 8.2 nm. ZFC-FC measurements revealed that the samples are ferromagnetic at room temperature. Nevertheless, due to the particle's nanometric size, a superparamagnetic-like behavior was evidenced with a blocking temperature (TB) below 60 K. M(H) loops were fitted using a distribution of Langevin functions, obtaining a maximum saturation magnetization Ms ~ 25 emu/g after 24 h of milling. Likewise, the FCB system is magnetically soft a room temperature with coercive field values below (132 Oe). Finally, Mössbauer spectroscopy showed that the superparamagnetic-like behavior could be associated with the Cu matrix's nanoparticle size and Fe atom behavior.

Effect of Silica Embedding on the Structure, Morphology and Magnetic Behavior of (Zn0.6Mn0.4Fe2O4)δ/(SiO2)(100-δ) Nanoparticles.

The effect of SiO2 embedding on the obtaining of single-phase ferrites, as well as on the structure, morphology and magnetic properties of (Zn0.6Mn0.4Fe2O4)δ(SiO2)100−δ (δ = 0–100%) nanoparticles (NPs) synthesized by sol-gel method was assessed. The phase composition and crystallite size were investigated by X-ray diffraction (XRD), the chemical transformations were monitored by Fourier transform infrared (FT-IR) spectroscopy, while the morphology of the NPs by transmission electron microscopy (TEM). The average crystallite size was 5.3–27.0 nm at 400 °C, 13.7–31.1 nm at 700 °C and 33.4–49.1 nm at 1100 °C. The evolution of the saturation magnetization, coercivity and magnetic anisotropy as a function of the crystallite sizes were studied by vibrating sample magnetometry (VSM) technique. As expected, the SiO2 matrix shows diamagnetic behavior accompanied by the accidentally contribution of a small percent of ferromagnetic impurities. The Zn0.6Mn0.4Fe2O4 embedded in SiO2 exhibits superparamagnetic-like behavior, whereas the unembedded Zn0.6Mn0.4Fe2O4 behaves like a high-quality ferrimagnet. The preparation route has a significant effect on the particle sizes, which strongly influences the magnetic behavior of the NPs.

Superparamagnetic Fe/Au Nanoparticles and Their Feasibility for Magnetic Hyperthermia

Today, magnetic hyperthermia constitutes a complementary way to cancer treatment. This article reports a promising aspect of magnetic hyperthermia addressing superparamagnetic and highly Fe/Au core-shell nanoparticles. Those nanoparticles were prepared using a wet chemical approach at room temperature. We found that the as-synthesized core shells assembled with spherical morphology, including face-centered-cubic Fe cores coated and Au shells. The high-resolution transmission microscope images (HRTEM) revealed the formation of Fe/Au core/shell nanoparticles. The magnetic properties of the samples showed hysteresis loops with coercivity (HC) close to zero, revealing superparamagnetic-like behavior at room temperature. The saturation magnetization (MS) has the value of 165 emu/g for the as-synthesized sample with a Fe:Au ratio of 2:1. We also studied the feasibility of those core-shell particles for magnetic hyperthermia using different frequencies and different applied alternating magnetic fields. The Fe/Au core-shell nanoparticles achieved a specific absorption rate of 50 W/g under applied alternating magnetic field with amplitude 400 Oe and 304 kHz frequency. Based on our findings, the samples can be used as a promising candidate for magnetic hyperthermia for cancer therapy.

Nickel ferrite ceramics: combustion synthesis, sintering, characterization, and magnetic and electrical properties

ABSTRACT Nickel ferrite powders were prepared by combustion synthesis of Fe, Fe2O3 and NiO using NaClO4 as fuel. Nickel ferrite ceramics were fabricated by single-step and two-step sintering under various conditions. The effects of each sintering process on the densification, microstructure and properties of the ceramics were investigated. X-ray diffraction analysis of as-prepared powders and as-fabricated ceramics confirmed a single-phase NiFe2O4 with a cubic spinel crystal structure. Single-step sintering produced ceramics with a wider density range (3.63–3.97 g/cm3) than two-step sintering (3.74–3.84 g/cm3) and a wider grain size range (1.10–2.31 µm compared to 1.30–1.37 µm). Two-step sintering produced ceramics with greater microhardness (135.00-172.60 HV) than single-step sintering (65.33-153.00 HV). In both methods, higher sintering temperatures produced ceramics with greater saturation magnetization (Ms). The highest Ms values were 62.84 emu/g from single-step sintering at 1200°C and 70.00 emu/g from two-step sintering at T2 = 1150°C: Hc was, respectively, 31.18 and 22.00 Oe. The ceramic sintered by the two-step method at T2 of 1150°C presented superparamagnetic-like behavior of multi-domain magnetic materials, with high µi and very low Hc. The higher electrical resistivity (R), dielectric constant (εr) and quality factor of this ceramic support high-frequency data storage applications.

Magnetic τ-MnAlC thin film fabrication by high-vacuum thermal evaporation

Polycrystalline τ-MnAlC thin films were produced by thermal evaporation technique in one-step deposition and using as target materials a homogeneous τ-MnAlC(100%) and a heterogeneous ε-MnAlC(73.9%)/τ-MnAlC(22.0%)/Al6Mn(4.1%) alloy, both keeping the same atomic percent for each constituent element. X-ray diffraction patterns evidence all films present a high concentration of the desired τ-phase. A microscopy analysis shows the thermal evaporation induces an island-type deposition of nanocrystalline grains with an average size of 9 nm. A hysteresis loop shows the highest concentration τ-MnAlC film exhibits a superparamagnetic-like behavior, an extremely important nanomagnetic state for the development of actuators and magnetic field sensor.

Impact of annealing temperature and ferrite content embedded in SiO2 matrix on the structure, morphology and magnetic characteristics of (Co0.4Mn0.6Fe2O4)δ (SiO2)100-δ nanocomposites

In this work, the (Co0.4Mn0.6Fe2O4)δ (SiO2)100-δ (δ = 0–100%) nanocomposites were synthesized via a modified sol-gel method followed by annealing at 200, 400, 700 and 1100 °C. The main purpose of this paper is to find a relationship between the nanoparticle structure and morphology and the magnetic parameters at different annealing temperatures and different ferrite contents embedded in the SiO2 matrix. The powder X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy were used to investigate the structural properties, such as crystalline phases, degree of crystallinity, crystallite size and the formation of chemical bonds, while transmission electron microscopy (TEM) was used to examine the morphological features of nanocomposites. The dependence of saturation and remanent magnetizations, coercivity and magnetic anisotropy on ferrite content embedded in SiO2 matrix were investigated by vibrating sample magnetometry (VSM). The XRD data showed that the crystallite size increase with increasing annealing temperature and amount of ferrite content embedded in the SiO2 matrix. The SiO2 matrix exhibits diamagnetic behavior with a small ferromagnetic fraction, Co0.4Mn0.6Fe2O4 embedded in SiO2 matrix presents superparamagnetic-like behavior, while unembedded Co0.4Mn0.6Fe2O4 a high-quality ferromagnetic type behavior.

Facile synthesis of superparamagnetic Fe3O4 nanoparticles at therapeutic temperature range for magnetic hyperthermia therapy

Superparamagnetic Fe3O4 nanoparticles have been synthesized using simple and ecofriendly hydrothermal method at supercritical conditions of ethanol. The morphology and crystal structure reveal cubic-like shape with an average size of 63 ± 30 nm and formation of FCC Fe3O4 phase structure. The magnetic properties exhibit superparamagnetic-like behavior at room temperature with saturation magnetization (Ms) of 108 emu/g and coercivity (HC) close to 0 Oe. The temperature dependence on magnetization measurements has confirmed the superparamagnetic behavior with blocking temperature TB of 320 K at the therapeutic temperature range of hyperthermia therapy at 42–47 °C. Feasibility for magnetic hyperthermia has been tested under applied AC magnetic field and frequency ranges from 100 to 500 Oe and 147 to 304 kHz, respectively. The findings confirm that Fe3O4 nanoparticles are feasible for magnetic hyperthermia treatment of cancer.

Controlled Synthesis and Characterization of Micrometric Single Crystalline Magnetite With Superparamagnetic Behavior and Cytocompatibility/Cytotoxicity Assessments

A new class of magnetite (Fe3O4) particles, coined as “Single Crystalline Micrometric Iron Oxide Particles” (SCMIOPs), were obtained by hydrothermal synthesis. Both the single Fe3O4 phase content and the particle sizes range, from 1 µm to 30 µm, can be controlled by synthesis. The notable finding states that these particles exhibit vanishing remanent magnetization (σr=0.28 emu/g) and coercive force (Hc=1.5 Oe), which indicate a superparamagnetic-like behavior (unexpected at micrometric particles size), and remarkably high saturation magnetization (σs=95.5 emu/g), what ensures strong magnetic response, and the lack of agglomeration after the magnetic field removal. These qualities make such particles candidates for biomedical applications, to be used instead of magnetic nanoparticles which inevitably involve some drawbacks like aglommeration and insufficient magnetic response. In this sense, cytocompatibility/cytotoxicity tests were performed on human cells, and the results have clearly indicated that SCMIOPs are cytocompatible for healthy cell lines HaCaT (human keratinocytes) and HEMa (primary epidermal melanocytes) and cytotoxic for neoplastic cell lines A375 (human melanoma) and B164A5 (murine melanoma) in a dose-dependent manner.

Influence of ferrite to silica ratio and thermal treatment on porosity, surface, microstructure and magnetic properties of Zn0.5Ni0.5Fe2O4/SiO2 nanocomposites

The evolution of structural and magnetic properties of Zn0.5Ni0.5Fe2O4/SiO2 nanocomposites with the ferrite content embedded in the SiO2 matrix and the annealing temperature was investigated. The results showed the increase of crystallite size (2.7–57.4 nm), saturation magnetization (0.36–82.4 emu/g), remanence magnetization (0.06–15.4 emu/g) and the decrease of specific pore volume (0.183–0.010 cm3/g) and specific surface area (≤0.5–247 m2/g) with the increase of Zn0.5Ni0.5Fe2O4 content embedded in the SiO2 matrix and the annealing temperature. The SiO2 matrix exhibits diamagnetic behavior with a small ferromagnetic fraction, Zn0.5Ni0.5Fe2O4 embedded in SiO2 matrix presents superparamagnetic-like behavior, while bulk Zn0.5Ni0.5Fe2O4 a high-quality ferromagnetic type behavior.

On the superparamagnetic behavior of BiFeO3-PbTiO3 nanoparticles

In this work, the nanostructuration effects on the physical properties of pure and La doped (0.6)BiFeO3-(0.4)PbTiO3 magnetoelectric nanoparticles were investigated. An exotic magnetic response, mimicking a superparamagneticlike behavior that raised the magnetization to levels never reported before for these materials, is clearly observed. Another important change associated with the nanostructuration is observed in the symmetry of the perovskite-structured materials, which changes from a tetragonal to a rhombohedral one. Transmission electron microscopic and X-ray diffraction results (investigated by the Debye-Scherrer method) revealed uniform nanoparticles of spherical shape, average particle sizes close to 5 nm and with a single structural domain (only one crystallite per particle). The pronounced increase (∼20 times) in the magnetization response of the nanoparticles, compared to microparticle ones, is observed in magnetization curves. A magnetic semiempirical phenomenological model, where noninteracting single-domain magnetic nanoparticles are considered, is used to fit the magnetization curves, revealing the almost absence of surface effects in a typical superparamagneticlike behavior. All these aspects pointing to a material with immense potential for practical applications in spintronics and magnetoelectronics.

Magnetic Graphene Oxide Nanocarrier for Targeted Delivery of Cisplatin: A Perspective for Glioblastoma Treatment.

Selective vectorization of Cisplatin (CisPt) to Glioblastoma U87 cells was exploited by the fabrication of a hybrid nanocarrier composed of magnetic γ-Fe2O3 nanoparticles and nanographene oxide (NGO). The magnetic component, obtained by annealing magnetite Fe3O4 and characterized by XRD measurements, was combined with NGO sheets prepared via a modified Hummer’s method. The morphological and thermogravimetric analysis proved the effective binding of γ-Fe2O3 nanoparticles onto NGO layers. The magnetization measured under magnetic fields up to 7 Tesla at room temperature revealed superparamagnetic-like behavior with a maximum value of MS = 15 emu/g and coercivity HC ≈ 0 Oe within experimental error. The nanohybrid was found to possess high affinity towards CisPt, and a rather slow fractional release profile of 80% after 250 h. Negligible toxicity was observed for empty nanoparticles, while the retainment of CisPt anticancer activity upon loading into the carrier was observed, together with the possibility to spatially control the drug delivery at a target site.

Unique Superparamagnetic-like Behavior Observed in Non-π-delocalized Nitroxide Diradical Compounds Showing Discotic Liquid Crystalline Phase.

A unique superparamagnetic-like behavior and a large "positive magneto-LC effect" were observed in the solid phases and the hexagonal columnar (Colh ) liquid crystalline (LC) phase, respectively, of novel achiral non-π-delocalized nitroxide diradical compounds (R,S)-1, which showed polymorphism in the solid phases (solids I and II). The SQUID magnetization measurement revealed that (1) (R,S)-1 containing a small amount of racemic diastereomers (R*,R*)-1 possessed an unusual and large temperature-independent magnetic susceptibility (χTIM >0) component in the original nanocrystalline solid I that was responsible for the observed superparamagnetic-like behavior under low magnetic fields and did not arise from the contamination by extrinsic magnetic metal or metal ion impurities, besides ordinary temperature-dependent paramagnetic susceptibility (χpara >0) and temperature-independent diamagnetic susceptibility (χdia <0) components, (2) a large increase in molar magnetic susceptibility (χM ) (positive magneto-LC effect) that occurred at the solid I-to-liquid crystal transition upon heating was preserved as an additional χTIM increase in the resulting polymorphic nanocrystalline solid II by cooling, and (3) such unique magnetic phenomena were induced by thermal processing for (R,S)-1 or by adding a small amount of (R*,R*)-1 to (R,S)-1 as the impurity.

Evidence of particle-particle interaction quenching in nanocomposite based on oleic acid-coated Fe3O4 nanoparticles after over-coating with essential oil extracted from Croton cajucara Benth

This study reports on the synthesis and characterization of oleic acid (OA)-coated Fe3O4 nanoparticles (Fe3O4@OA) and AO plus essential oil (EO)-coated Fe3O4 nanoparticles (Fe3O4@OA/EO). The EO was extracted from Croton cajucara Benth (CCB) leaves; a plant from the Brazilian Amazon region. Structural and morphological characterizations were carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM) images, respectively. Additionally, thermogravimetric analysis and magnetization measurements (hysteresis cycle, zero field-cooled-ZFC, field-cooled-FC, and AC susceptibility) were used to assess thermal and magnetic properties of the as-fabricated samples. Rietveld refinement of XRD pattern confirmed the formation of magnetite phase with no extra phases, whereas TEM images revealed spherically-shaped nanoparticles in the Fe3O4@OA and (Fe3O4@OA/EO) samples with a mean physical size of 8.5 nm and 10.1 nm, respectively. ZFC and FC curves revealed the occurrence of blocked/frozen state below the maximum peak (Tmax) at ∼81 K and ∼40 K for the Fe3O4@OA and (Fe3O4@OA/EO) samples, respectively. Moreover, low-temperature AC susceptibility vs. T curves recorded in the range of 0.2–1000 Hz showed that the OA coating of the Fe3O4 nanoparticles leads to a spin-glass-like behavior credited to the strong particle-particle interactions; meanwhile, the double layer (AO + EO) coating of the Fe3O4 nanoparticles remarkably quenches the particle-particle interaction leading to a superparamagnetic-like behavior.

Magnetite nanoparticles with controlled sizes via thermal degradation of optimized PVA/Fe(III) complexes

In this manuscript, magnetite nanoparticles have been synthesized via an optimized method that consists in the thermal degradation of a polymer-metal complex prepared from an appropriated mix of polyvinyl alcohol and iron nitrate. Negatively charged (Zeta potential) nanoparticles, with a cubic spinel structure (▪ space group) and a narrow size distribution (mean particle size close to 5 nm) were successfully processed. Magnetic characterizations reveal a single-domain superparamagnetic-like behavior with a decreased saturation magnetization (11 emu/g) due to surface effects. Nanoparticle dispersions were investigated by SAXS (hard spheres, Beaucage model) and the average gyration radius (2.1 nm) and Porod’s length (2.4 nm) are found to be close to the nanoparticle’s physical and magnetic sizes. The results revealed that this easy, reproducible and cheap method is suitable to synthesize high-quality single-domain magnetite nanoparticles that can be functionalized for future biological applications.