Superparamagnetic-like Behavior Research Articles

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.

Influence of polyelectrolyte chains on surface charge and magnetization of iron oxide nanostructures

The layer-by-layer (LbL) technique was employed to encapsulate maghemite (γ-Fe2O3) nanoparticles with natural and synthetic polyelectrolytes, with a view to producing magnetic nanoplatforms as a tool to improve remotely assisted delivery/release of hydrophobic drugs and to address their low cargo capacity. Magnetic nanoparticles (MNPs) were synthesized by coprecipitation and functionalized with the layer-by-layer (LbL) assembly of polyelectrolyte multilayers. Simultaneous conductimetric and potentiometric titrations were utilized in order to find the optimal pH for the deposition of four intercalated layers of polystyrene sulfonate (PSS)/polyallylamine hydrochloride (PAH) or sodium carboxymethylcellulose (CMC)/chitosan (CHI) polyelectrolytes. XRD, TEM, DLS, TGA and FTIR techniques were utilized to access structural, morphological and surface properties. Charge reversals after each deposition confirmed a stable LbL assembly adsorbed on a multiparticulate nucleus (∼64 nm) of 8.8 nm-sized MNPs. Polymer layers of increasing thickness ranging from 4 to 15 nm (PSS/PAH) and from 21 to 48 nm (CMC/CHI) were estimated as MNPs were successively coated with polyelectrolytes. All the systems exhibited superparamagnetic-like behavior. Surprisingly, a stronger reduction was observed in the saturation magnetization of MNPs coated with synthetic polyelectrolytes (thinner shells) than in the system layered with natural polymers (thicker shells). Magnetization results suggest that synthetic polyelectrolytes adsorbed on the nanoparticle surface appear to have a stronger cooperativity than that of biopolymers, which could differently affect the interaction of spins located in the magnetically disordered regions in the nanoparticle surface.

Dynamic behavior of magnetic hybrid films of polyvinyl butyral/iron oxide nanoparticles (PVB/Fe2O3) for their control as microactuators

Polymeric magnetic hybrid materials (PMHM) are a motivating research topic for microactuator technologies, as flexible magnetic devices or contactless manipulation, useful for many applications. However, the control of these microactuators remains a challenge due to the severe performances required and the nonlinear dynamics that typify them. This study performs an exhaustive experimental characterization of the nonlinear dynamics of a PMHM-film as a cantilever actuator. The PMHM-film consists of polyvinyl butyral (PVB) with iron oxide (Fe2O3) nanoparticles synthesized in-situ, at two different nominal concentrations of FeCl2·4H2O. This work presents the synthesis of the PMHM-films (PVB/Fe2O3), their magnetic and morphological characterization, and the dynamic characterization at constant and sine magnetic fields. Magnetic characterization showed a superparamagnetic-like behavior of the material at room temperature, in accordance with previous works. A damped-like behavior is exposed with a maximum displacement of 0.99 mm when a constant magnetic field of 0.96 kOe is applied. In the sine magnetic field test, a nonlinear response and rate-dependent behavior when the frequency is increased were observed. Future work will consider the physical model of the dynamic behavior of the (PVB/Fe2O3) films and a control system to reduce the hysteresis nonlinearities.

Magnetic characteristics of M2FeV3O11 (M = Mg, Zn, Pb, Co, Ni) compounds

The unusual physical characteristics of the multicomponent oxide systems renewed the interest as the potential cathode materials in high-energy cells. Since the earlier magnetic characteristics were not entirely conclusive, we report the results of dc magnetic measurements including higher harmonics of ac magnetic susceptibility of the M2FeV3O11 (M=Mg, Zn, Pb, Co, Ni) compounds. Ferrimagnetic long-range and antiferromagnetic short-range interactions for all compounds under study at low temperatures as well as superparamagnetic-like behavior with the blocking temperature of 29K and the freezing parameter of 0.013 were observed. These effects are discussed within the framework of superexchange and double exchange magnetic interactions as well as the mixed valence band of iron ions.

Laser irradiation of iron, cobalt, and nickel targets in liquid nitrogen: A facile approach for nitride nanoparticle fabrication of ferromagnetic transition metals

Nitride nanoparticles of ferromagnetic metal elements were produced by laser irradiation from metallic targets immersed in liquid nitrogen using Nd:YAG lasers with wavelengths of 532 and 1024 nm. Transmission electron microscopy analyses of the precipitated nanoparticles from the suspensions on microscopy grids reveal agglomerates consisting of polydisperse particles with sizes in the tens of nanometers range. Some particles with size of several hundreds of nanometers indicate that laser irradiation promotes cryoablation together with plasma erosion of the targets. Selected area electron diffraction analyses corroborated by Raman measurements indicate the formation of crystalline metal nitrides with spheroidal and acicular morphologies. Regardless of the laser radiation wavelength, nanoparticles with similar nitride phases are found: Fe4N and Fe16N2 for Fe target, Co2N and Co3N for Co target, Ni4N with Ni8N for Ni target. All nanoparticles show superparamagnetic-like behavior with a blocking temperature varying significantly with the nanoparticle size. Such single-step method is a promising green route for nanoparticle production of these metal nitrides, which are commonly obtained using more complex and multi-step processes.

Superparamagnetic iron oxide nanodiscs for hyperthermia therapy: Does size matter?

For the final realization of magnetic nanoparticles (MNPs) mediated hyperthermia as a viable clinical therapy for cancer treatment, it is necessary to devise novel approaches in order to improve the heating efficiency or Specific Loss Parameter (SLP) of these MNPs. Recently, it has been shown that magnetic nanodiscs with enhanced shape anisotropy, diameters around 200 nm (25 nm thick), and vortex magnetic domain structure exhibit very high SLP values. Despite their high heating efficiency, biomedical applications of these nanodiscs could not be hassle-free due to their relatively big size. Therefore, in this work, we have studied how the heating efficiency of the nanodiscs changes upon size reduction (∼12 nm diameter and ∼3 nm thickness). In addition, we have compared these results with those obtained for more typically studied spherical nanoparticles of similar volume. Transmission Electron microscopy, Atomic Force Microscopy and X-ray Diffraction confirm the disc shape of our MNPs and that they are mostly composed of iron oxide (Fe3O4 or γ-Fe2O3) phase. Magnetometry indicates that the nanodiscs do not exhibit a vortex magnetic domain structure, but still present a superparamagnetic-like behavior, with zero magnetization in the absence of field at room temperature (ideal for biomedical applications) and enhanced effective anisotropy as compared to the spherical nanoparticles. Finally, calorimetric methods based magnetic hyperthermia experiments indicate that the SLP values for these small nanodiscs are much lower than those reported for the bigger disc-shaped nanoparticles, but these superparamagnetic nanodiscs act as better heating mediators than the spherical nanoparticles of similar volume.

Elaboration and Magnetic Properties of Cobalt-Palladium Magnetic Nanowires Encapsulated in Carbon Nanotubes

Bimetallic one-dimensional (1-D) cobalt-palladium magnetic nanowires encapsuled by carbon nanotubes were synthesized on silicon substrate using plasma enhanced chemical vapor deposition technique. After the deposition of the catalyst, the growth of nanotubes takes place in two stages. The first is a thermal pretreatment to transform continuous nanometer bimetallic thick film into isolated and uniformly distributed nanoparticles over the entire surface of the substrate. The second step results in the growth of nanotubes perpendicular to the substrate by the addition of carbon atoms on the insulated metal nanoparticles. While growing the nanotubes at given thermochemical conditions, a Co-Pd eutectic is thought to diffuse inside the cavity of the nanotube along a length of few hundreds of nanometers as determined by high resolution, spatially resolved Electron Energy Loss Spectroscopy (EELS), and energy filtered elemental mapping. The magnetic anisotropy along the nanotube directions is observed. Ferromagnetic or superparamagnetic-like behavior of the filled nanotubes was measured through local magneto-optical Kerr effect or global superconducting quantum interference device measurements, respectively. Information on the magnetism of filled nanotubes at different scales is pointed out and discussed.

The impact of the chemical synthesis on the magnetic properties of intermetallic PdFe nanoparticles

Palladium-rich Iron nanoparticles in the 4–8 nm range have been produced by a combination of two methods: the thermal decomposition of organometallic precursors and the reduction of metallic salts by a polyol. Herein, it is shown how the details of the synthesis have a striking impact on the magnetic and morphological properties of the final products. In the synthesis of these bimetallic nanoparticles, the use of high reaction temperatures plays an essential role in attaining good chemical homogeneity, which has proved to have a key influence on the magnetic properties. Magnetic characterization has been performed by electron magnetic resonance and magnetization measurements, which have confirmed the superparamagnetic-like behavior at room temperature. No clear traces of magnetic polarization in palladium atoms have been detected. The combination of long-term stability and homogeneous chemical and magnetic properties makes these particles very suitable for a wide range of applications in nanotechnology.

Superparamagnetic properties of carbon nanotubes filled with NiFe2O4 nanoparticles

Multi walled carbon nanotubes (MWCNTs) were successfully synthesized using custom-made 80 nm pore-size alumina templates, and were uniformly filled with nickel ferrite (NFO) nanoparticles of 7.4 ± 1.7 nm diameter using a novel magnetically assisted capillary action method. X-ray diffraction confirmed the inverse spinel phase for the synthesized NFO. Transmission electron microscopy confirms spherical NFO nanoparticles with an average diameter of 7.4 nm inside MWCNTs. Magnetometry indicates that both NFO and NFO-filled MWCNTs present a blocking temperature around 52 K, with similar superparamagnetic-like behavior, and weak dipolar interactions, giving rise to a super-spin-glass-like behavior at low temperatures. These properties along with the uniformity of sub-100 nm structures and the possibility of tunable magnetic response in variable diameter carbon nanotubes make them ideal for advanced biomedical and microwave applications.

Modulation of Magnetic Heating via Dipolar Magnetic Interactions in Monodisperse and Crystalline Iron Oxide Nanoparticles

In the pursuit of controlling the heat exposure mediated by magnetic nanoparticles, we provide new guidelines for tailoring magnetic relaxation processes via dipolar interactions. For this purpose, highly crystalline and monodisperse magnetic iron oxide nanocrystals whose sizes range from 7 to 22 nm were synthesized by thermal decomposition of iron organic precursors in 1-octadecene. The as-synthesized nanoparticles are soft nanomagnets, showing superparamagnetic-like behavior and SAR values which progressively increase with particle size, field frequency, and amplitude up to 3.6 kW/gFe. Our data show the influence of media viscosity, particle size, and concentration on dipolar interactions and consequently on the magnetic relaxation processes related to the heat release. Understanding the role of dipolar interactions is of great importance toward the use of iron oxide nanoparticles as efficient hyperthermia mediators.

Effect of sintering pressure on structure and magnetic properties of Zn0.99Ni0.01O bulk samples synthesized under different pressures

A series of Zn0.99Ni0.01O bulk samples were prepared by a coprecipitation method, and then sintered at 600°C under various pressures from normal pressure(NP) to 3GPa. The effects of sintering pressure (PS) on the structure, morphology and magnetic properties of the doping samples were investigated in detail. The XRD and HRTEM results reveal that all samples are of single-phase hexagonal structure. Compared with the sample sintered at normal pressure, the lattice parameters a and c of the samples sintered at high pressures (HP) show a sharply decrease. With the increase of sintering pressure, the particle size gradually increases as well as the particles get closer to each other. At 300K, the sample sintered at normal pressure shows a superparamagnetic-like behavior, while the samples sintered at high pressures display typical ferromagnetic behaviors. The saturation magnetization of the samples sintered at high pressures is three orders of magnitude larger than that of the one sintered at normal pressure. Our results reveal that an appropriate sintering pressure can tune the magnetic properties of Ni-doped ZnO system by changing the lattice parameters, particle size and inter-particle spacing, which may be helpful to the practical applications.

Large-Scale Synthesis of Colloidal Fe3O4 Nanoparticles Exhibiting High Heating Efficiency in Magnetic Hyperthermia

Exceptional magnetic properties of magnetite, Fe3O4, nanoparticles make them one of the most intensively studied inorganic nanomaterials for biomedical applications. We report successful gram-scale syntheses, via hydrothermal route or controlled coprecipitation in an automated reactor, of colloidal Fe3O4 nanoparticles with sizes of 12.9 ± 5.9, 17.9 ± 4.4, and 19.8 ± 3.2 nm. To investigate structure–property relationships as a function of the synthetic procedure, we used multiple techniques to characterize the structure, phase composition, and magnetic behavior of these nanoparticles. For the iron oxide cores of these nanoparticles, powder X-ray diffraction and electron microscopy both confirm single-phase Fe3O4 composition. In addition to the core composition, the magnetic performance of nanoparticles in the 13–20 nm size range can be strongly influenced by the surface properties, which we analyzed by three complementary techniques. Raman scattering and X-ray photoelectron spectroscopy (XPS) measurements indicate overoxidation of nanoparticle surfaces, while transmission electron microscopy (TEM) shows no distinct core–shell structure. Considered together, Raman, XPS, and TEM observations suggest that our nanoparticles have a gradually varying nonstoichiometric Fe3O4+δ composition, which could be attributed to the formation of Fe3O4–γ-Fe2O3 solid solutions at their outermost surface. Detailed analyses by TEM reveal that the hydrothermally produced samples include single-domain nanocrystals coexisting with defective twinned and dimer nanoparticles, which form as a result of oriented-attachment crystal growth. All our nanoparticles exhibit superparamagnetic-like behavior with a characteristic blocking temperature above room temperature. We attribute the estimated saturation magnetization values up to 84.01 ± 0.25 emu/g at 300 K to the relatively large size of the nanoparticles (13–20 nm) coupled with the syntheses under elevated temperature; alternative explanations, such as surface-mediated effects, are not supported by our spectroscopy or microscopy measurements. For these colloids, the heating efficiency in magnetic hyperthermia correlates with their saturation magnetization, making them appealing for therapeutic and other biomedical applications that rely on high-performance nanoparticle-mediated hyperthermia.

Characterization of partially inverse spinel ZnFe2O4 with high saturation magnetization synthesized via soft mechanochemically assisted route

ZnFe2O4 was prepared by a soft mechanochemical route from two starting combinations of powders: (1) Zn(OH)2/α-Fe2O3 and (2) Zn(OH)2/Fe(OH)3 mixed in a planetary ball mill. The mechanochemical treatment provoked reaction leading to the formation of the ZnFe2O4 spinel phase that was monitored by XRD, TEM, IR and Raman spectroscopy. The spinel phase was first observed after 4h of milling and its formation was completed after 18h in both the cases of starting precursors. The synthesized ZnFe2O4 has a nanocrystalline structure with a crystallite size of about 20.3 and 17.6nm, for the cases (1) and (2), respectively. In the far-infrared reflectivity spectra are seen four active modes. Raman spectra suggest an existence of mixed spinel structure in the obtained nanosamples. In order to confirm phase formation and cation arrangement, Mössbauer measurements were done. Estimated degree of inversion is about 0.58 for both starting mixtures. The magnetic properties of the prepared ZnFe2O4 powders were also studied. The results show that the samples have a typical superparamagnetic-like behavior at room temperature. Higher values of magnetization in the case of samples obtained with starting mixture (2) suggest somewhat higher degree of cation inversion.

Dielectric and magnetic properties of CdMoO4:Gd3+ single crystal

Broadband dielectric spectroscopy and magnetic measurements provide experimental evidence that the CdMoO4:Gd3+ single crystal is the paramagnet with low relative dielectric permittivity (εr∼8), which slightly depends on the temperature and frequencies. Magnetization with zero coercivity and remanence is almost a universal function of μ0H/T, characterizing superparamagnetic-like behavior. These results are being considered in a framework of the random distribution of the Ga3+ ions in the tetragonal structure.

A Study of the Origin of Weak Ferromagnetism in Zn1−x Co x O

To study the origin of ferromagnetism in Zn1−xCoxO thin films, its thermal diffusivity, in addition to its magnetization measurements, were analyzed. Thin films of Zn1−xCoxO (x = 0.03) were deposited on Si (100) substrates through ultrasonic spray pyrolysis. Magnetization M(B) measurements at low temperature showed a hysteresis loop that indicated the existence of ferromagnetic ordering in Zn0.97Co0.03O. However, the magnetic moment per Co ion was much lower than expected. A comparison of M(T) measured at zero-field-cooled and field-cooled conditions showed a superparamagnetic-like behavior, with a blocking temperature of about 130 K. Temperature dependence on the thermal diffusivity of Zn0.97Co0.03O showed a pronounced lambda-shaped minimum at 130 K, which indicated the existence of a second-order phase transition at this temperature. The weak ferromagnetism in the Zn0.97Co0.03O with the Curie temperature of 130 K was ascribed to the uncompensated magnetic moment at the surface of CoO nanoclusters.

Cooperative Organization in Iron Oxide Multi-Core Nanoparticles Potentiates Their Efficiency as Heating Mediators and MRI Contrast Agents

In the pursuit of optimized magnetic nanostructures for diagnostic and therapeutic applications, the role of nanoparticle architecture has been poorly investigated. In this study, we demonstrate that the internal collective organization of multi-core iron oxide nanoparticles can modulate their magnetic properties in such a way as to critically enhance their hyperthermic efficiency and their MRI T(1) and T(2) contrast effect. Multi-core nanoparticles composed of maghemite cores were synthesized through a polyol approach, and subsequent electrostatic colloidal sorting was used to fractionate the suspensions by size and hence magnetic properties. We obtained stable suspensions of citrate-stabilized nanostructures ranging from single-core 10 nm nanoparticles to multi-core magnetically cooperative 30 nm nanoparticles. Three-dimensional oriented attachment of primary cores results in enhanced magnetic susceptibility and decreased surface disorder compared to individual cores, while preserving a superparamagnetic-like behavior of the multi-core structures and potentiating thermal losses. Exchange coupling in the multi-core nanoparticles modifies the dynamics of the magnetic moment in such a way that both the longitudinal and transverse NMR relaxivities are also enhanced. Long-term MRI detection of tumor cells and their efficient destruction by magnetic hyperthermia can be achieved thanks to a facile and nontoxic cell uptake of these iron oxide nanostructures. This study proves for the first time that cooperative magnetic behavior within highly crystalline iron oxide superparamagnetic multi-core nanoparticles can improve simultaneously therapeutic and diagnosis effectiveness over existing nanostructures, while preserving biocompatibility.

Synthesis, structural and electrical properties of triethylene glycol (TREG) stabilized Mn0.2Co0.8Fe2O4 NPs

Triethylene glycol (TREG) stabilized Mn0.2Co0.8Fe2O4 NPs was synthesized by a glycothermal reaction. XRD analysis identified the product as Mn0.2Co0.8Fe2O4 with a high phase purity. Nano-sized particles with an average size of about 6–8nm were obtained with nearly single crystalline nature with TEM analysis. Superparamagnetic-like behavior of TREG stabilized Mn0.2Co0.8Fe2O4 NPs was observed by VSM. The binding between TREG and Mn0.2Co0.8Fe2O4 NPs was investigated with FT-IR and found to be via O on the TREG and NP surface. TG analysis indicated that the Mn0.2Co0.8Fe2O4 NP content was about 40%, with a TREG-shell content to be around 60%. Overall conductivity of the nanocomposite is in the range of 10−10 to 10−7Scm−1 with a strong dependence on temperature and frequency, indicating ionic conductivity. The nanocomposite exhibited lower ɛ’ and ɛ″ compared to TREG stabilized Mn0.2Co0.8Fe2O4 NPs due to the doping of co-doping of manganese and cobalt.

Poly(ethylene glycol)-Coated Fe3 O4 Nanoparticles by UV-Thiol-Ene Addition of PEG Dithiol on Vinyl-Functionalized Magnetite Surface

Magnetite nanoparticles are synthesized and functionalized with vinyl groups (by silanization reaction with VTMS) and further coated with poly(ethylene glycol) dithiol under UV activation via thiol-ene addition. TEM analysis is in a good agreement with DLS analyses and shows that by vinyl functionalization and following PEG coating it was possible to achieve nanometer-sized particles with an average size of about 20–50 nm, well distributed and not-aggregated. Superparamagnetic-like behavior of coated Fe3O4 nanoparticles, which is typically looked for in biomedical applications, is ensured by the Brownian motion of the magnetic NPs in the ferrofluid. The polymeric coating does not modify the magnetic response of the magnetite nanoparticles.

Thermal Diffusivity Study of Weak Ferromagnetism in Zn1?xCoxO

Thermal diffusivity measurements have been conducted in order to study the origin of ferromagnetism in Zn1−xCoxO. Thin films of Zn1−xCoxO (x = 0.03) were deposited on Si (100) substrates by using ultrasonic spray pyrolysis. Magnetization M(H) measurements at low temperaturs show a hysteresis loop, which indicates the existence of ferromagnetic ordering in Zn0.97Co0.03O. However, the magnetic moment per Co ion is much lower than expected. A comparison of M(T) measured at zero-field-cooled (ZFC) and at field-cooled (FC) conditions shows a superparamagnetic-like behavior, and the blocking temperature is about 130 K. The temperature dependence of the thermal diffusivity of Zn0.97Co0.03O shows a pronounced lambda-shaped minimum at 130 K, which indicates the existence of a second-order phase transition at that temperature. The weak ferromagnetism in Zn0.97Co0.03O with a Curie temperature of 130 K is ascribed to an uncompensated magnetic moment at the surface of CoO nanoclusters with radii of about 1 nm.