Ferrimagnetic Nanoparticles Research Articles

Magnetic anisotropy and core-shell structure origin of the biogenic ferrihydrite nanoparticles

Ferrihydrite is a low-crystalline nanoscale matter. The uncompensated magnetic moment of the ferrihydrite caused by the antiferromagnetic ordering of the magnetic moments of iron atoms and leads to the magnetic properties very similar to those of ferro- and ferrimagnetic nanoparticles. In this study, we investigated the biogenic ferrihydrite nanoparticles with the narrow size distribution and an average diameter of ≈2 nm obtained by the bacteria life cycle. The features caused by the surface effects and the inhomogeneous structure of ferrihydrite have been examined in the temperature range of 4–300 K using Mössbauer spectroscopy and magnetometry. Based on the Mössbauer data, we identified the superparamagnetic blocking temperature at the temperature of 30 K for the largest ferryhidrite particles. We established that the exceptional magnetic anisotropy of ferrihydrite (KV=1.2⋅105 erg/cm3 and KS=0.1 erg/cm2) is reached because of the highly developed ferrihydrite nanoparticles’ surface. According to the Mössbauer data, we propose a core-shell structural model of the biogenic ferrihydrite particles. We found that the size of the dense core depends on the particle size. The well-crystallized core is formed only for nanoparticles larger than ≈2 nm, whereas smaller particles consist entirely of a matter with a lower density of iron atoms.

Bad neighbour, good neighbour: how magnetic dipole interactions between soft and hard ferrimagnetic nanoparticles affect macroscopic magnetic properties in ferrofluids.

Fluids responding to magnetic fields (ferrofluids) offer a scene with no equivalent in nature to explore long-range magnetic dipole interactions. Here, we studied the very original class of binary ferrofluids, embedding soft and hard ferrimagnetic nanoparticles. We used a combination of X-ray magnetic spectroscopy measurements supported by multi-scale experimental techniques and Monte-Carlo simulations to unveil the origin of the emergent macroscopic magnetic properties of the binary mixture. We found that the association of soft and hard magnetic nanoparticles in the fluid has a considerable influence on their inherent magnetic properties. While the ferrofluid remains in a single phase, magnetic interactions at the nanoscale between both types of particles induce a modification of their respective coercive fields. By connecting the microscopic properties of binary ferrofluids containing small particles, our findings lay the groundwork for the manipulation of magnetic interactions between particles at the nanometer scale in magnetic liquids.

Evidence of the Superparamagnetic State in the Zero-Field Microwave Susceptibility Spectra of Ferrimagnetic Nanoparticles

We investigated the static and dynamic magnetic properties of Zn0.4Fe2.6O4 nanoparticles synthesized by thermal decomposition. Two ranges of diameter were used: small particles (diameter about 6.2 nm) and larger ones (diameter about 22.4 nm). The nanoparticle microstructure was characterized by transmission electron microscopy. The temperature dependence of the zero-field dynamic permeability for both nanoparticle sizes was studied, revealing a superparamagnetic state for the small ones. Effects of the nanoparticle size on the dynamic permeability were analyzied, and linked to the superparamagnetic state. A dynamic susceptibility model was found to reproduce the experimental behavior as well as its temperature dependence.

Synthesis and study of γ-Fe2O3 and CoFe2O4 based ferrofluids by means of spectroscopic Mueller matrix ellipsometry

Ferrofluids are colloidal suspensions generally composed of ferromagnetic or ferrimagnetic nanoparticles (NPs). In the present study, the authors have focused on the ellipsometric characterization of two types of ferrofluids: one constituting maghemite (γ-Fe2O3) NPs and the other cobalt ferrite (CoFe2O4) NPs. The optical properties of the NPs are extracted from the ellipsometric spectra by using the Maxwell–Garnett effective medium approximations. As expected, Mueller matrix measurements reveal that the ferrofluid becomes anisotropic under the influence of a magnetic field. The authors correlate this anisotropy to the preferential orientation of NPs along the magnetic field.

Magnetic behaviors of spinel ferrite nanoparticles: a Monte Carlo simulation

Iron oxide nanoparticles with different phases (α-Fe2O3, γ-Fe2O3 and Fe3O4) are classified as the substantial transition metal oxides taking advantage of technological importance. The results of a Monte Carlo study of magnetic ordering in selectively spinel nanoparticles are discussed. The classical spin model with the Heisenberg-type interactions was used with superexchange interaction term. Different types of selective structures were studied in the framework of crystalline spinel structures with perfect or disordered surface and dilution of octahedral sublattice. The results are compared for various degrees of magnetic competition between first neighbor’s interactions in inverse or mixed spinel nanoparticles. The results permit us to explain the variation in saturation magnetization and give a better insight into the complex interplay between cationic distribution and magnetic disorder in ferrimagnetic nanoparticles.

Shape Effect in Magnetohydrodynamic Free Convection Flow of Sodium Alginate-Ferrimagnetic Nanofluid

This article presents the generalization of the unsteady MHD free convection flow of non-Newtonian sodium alginate-ferrimagnetic nanofluid in two infinite vertical parallel plates. The different shape (blade, brick, cylinder, and platelet) ferrimagnetic nanoparticles are dissolved in the non-Newtonian sodium alginate (SA) as base fluid to form non-Newtonian nanofluids. The Jeffrey fluid model together with energy equation is considered to demonstrate the flow. The Atangana–Baleanu fractional operator is utilized for the generalization of mathematical model. The Laplace transform technique and Zakian's numerical algorithm are used to developed general solutions with a fractional order for the proposed model. The obtained results are computed numerically and presented graphically to understand the physics of pertinent flow parameters. It is noticed that the velocity and temperature profiles are significantly increased with the increasing values of the fractional parameter due to the variation in thermal and momentum boundary layers. In the case of the effect of different shapes of nanoparticles, density is a dominant factor as compared to thermal conductivity, which significantly affects the flow of non-Newtonian nanofluid.

Structural and Magnetic Properties of Six-Line Ferrihydrite Nanoparticles

Magnetic properties of antiferromagnetic nanoparticles are not as straight forward as for ferromagnetic and ferrimagnetic nanoparticles. We analyzed the data of antiferromagnetic six-line ferrihydrite nanoparticles by considering distribution in particle magnetic moment. The fit of magnetization data, using non-linear least square fit procedure, considering Langevin function with and without distribution in particle magnetic moment, is presented. Magnetization of the system is measured as function of temperature and applied magnetic field.

Facile synthesis of magnetic nanoparticles optimized towards high heating rates upon magnetic induction

Abstract Inductively heatable magnetic particles are powerful additives towards smart processes, such as bonding and debonding on demand or self-healing. For the best efficiency, particles are needed which possess the highest possible heating rates/specific absorption rate when being exposed to a magnetic induction field. Herein, a cheap, simple and upscalable precipitation-oxidation assisted aging synthesis route for magnetic nanoparticles is optimized towards yielding a product with high heating rates. In-depth synthesis parameter studies were carried out to understand how the nanoparticle structure can be influenced in a way to yield the best heating rates. This included variation of the precursors chemistries, precipitant concentration, the oxidation and aging conditions as well as the co-doping of the particles with Zn and Co. A correlation between magnetic hysteresis, measured via vibrating sample magnetometry and specific absorption rate of the samples was established and it was demonstrated how crucial it is to select the right range of external magnetic fields in hysteresis measurements in order to achieve reliable and predictable correlations with the specific absorption power and heating rates, respectively. Via the established understanding and the systematic variation, it was ultimately possible to develop a synthesis procedure, yielding ferrimagnetic iron oxide nanoparticles that come with specific absorption rates of up to 1474 W·g−1 (at a magnetic field of 430 Oe at 1013 kHz).

Ectosymbiotic bacteria at the origin of magnetoreception in a marine protist.

Mutualistic symbioses are often a source of evolutionary innovation and drivers of biological diversification1. Widely distributed in the microbial world, particularly in anoxic settings2,3, they often rely on metabolic exchanges and syntrophy2,4. Here, we report a mutualistic symbiosis observed in marine anoxic sediments between excavate protists (Symbiontida, Euglenozoa)5 and ectosymbiotic Deltaproteobacteria biomineralizing ferrimagnetic nanoparticles. Light and electron microscopy observations as well as genomic data support a multi-layered mutualism based on collective magnetotactic motility with division of labour and interspecies hydrogen-transfer-based syntrophy6. The guided motility of the consortia along the geomagnetic field is allowed by the magnetic moment of the non-motile ectosymbiotic bacteria combined with the protist motor activity, which is a unique example of eukaryotic magnetoreception7 acquired by symbiosis. The nearly complete deltaproteobacterial genome assembled from a single consortium contains a full magnetosome gene set8, but shows signs of reduction, with the probable loss of flagellar genes. Based on the metabolic gene content, the ectosymbiotic bacteria are anaerobic sulfate-reducing chemolithoautotrophs that likely reduce sulfate with hydrogen produced by hydrogenosome-like organelles6 underlying the plasma membrane of the protist. In addition to being necessary hydrogen sinks, ectosymbionts may provide organics to the protist by diffusion and predation, as shown by magnetosome-containing digestive vacuoles. Phylogenetic analyses of 16S and 18S ribosomal RNA genes from magnetotactic consortia in marine sediments across the Northern and Southern hemispheres indicate a host-ectosymbiont specificity and co-evolution. This suggests a historical acquisition of magnetoreception by a euglenozoan ancestor from Deltaproteobacteria followed by subsequent diversification. It also supports the cosmopolitan nature of this type of symbiosis in marine anoxic sediments.

Smart elastomeric hydrogel of polyacrylamide containing nanosized barium ferrite and graphene oxide

Smart elastomeric hydrogels based on polyacrylamide containing ferrimagnetic nanoparticles of BaFe12O19 alone or a combination of BaFe12O19 and graphene oxide were synthesized. An improvised sample preparation technique was evolved to design actuators, where the hydrogel samples in rolls form were inserted into cut pieces of hard plastic sleeve in order to fabricate a lab-level actuator. The magneto-responsive actuation behaviour was measured by applying an external magnetic field with the help of a hand-held square type of NdFeB magnet. While the sample containing only 20 wt% BaFe12O19 exhibited only 15 mm deflection at threshold magnetic field of 28 mT, the deflection was significantly enhanced up to 23 mm for the sample containing 1 wt% GO and 20 wt% BaFe12O19 at a threshold magnetic field of 36.7 mT. Up to 20 wt% BaFe12O19, the hydrogels showed a heterogeneous dispersion of large-sized BaFe12O19 clusters and addition of a small percentage, e.g. 1% of GO resulted in significant improvement in the homogeneity of dispersion as well as reduction of the scale of the BaFe12O19 clusters. The saturation magnetization value of the hydrogels was also improved by 50–75% due to the addition of 1 wt% GO with 20 wt% BaFe12O19.

Morphological and magnetic response of copper-substituted nickel ferrite nanoparticles

ABSTRACTFerrite nanoparticles are interesting materials owing to their unique physical and chemical properties. The metal-doped ferrites have well-defined structures and magnetic response, such as high permeability for a specific frequency range. In this study, copper-substituted nickel ferrite (Ni1−xCuxFe2O4) nanoparticles with a compositional range of 0 ≤ x ≤ 0.3 were synthesised through a co-precipitation technique. Metal chlorides were used as precursors and NaOH as a precipitating agent for the growth of ferrite nanoparticles. To minimise the internal stresses and maximise the magnetic response, ferrite nanoparticles were annealed in a furnace at 700°C for 6 h. The structural and magnetic response of Ni1−xCuxFe2O4 ferrite with different values of x were investigated using Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectroscopy (FT-IR), Vibrating Sample Magnetometer (VSM) and X-ray Diffraction (XRD) techniques. XRD analysis confirmed the formation of cubic spinel structure of single phase for all the compositions. The lattice constant decreased with increase in the value of x. FT-IR study showed two main metal oxygen bonds in the range 500–700 cm−1 confirming the formation of a single-phase cubic inverse structure of Cu-substituted Ni ferrite. VSM results revealed the formation of ferrimagnetic nanoparticles. The optical and magnetic response of the ferrite nanoparticles changed with Cu content.

Liquid crystalline poly(propylene imine) dendrimer-based iron oxide nanoparticles.

Poly(propylene imine) dendromesogens (generations from 1 to 4) have been utilized for the synthesis and stabilization of ferrimagnetic Fe2O3 nanoparticles. Reduction of Fe(iii) with further oxidation of Fe(ii) results in the formation of highly soluble nanocomposites of iron oxides in a dendrimer, which are stable under a wide range of temperatures. The magnetic iron oxide nanoparticles were investigated by MALDI-ToF MS spectrometry and elemental analysis. To establish the type of mesophase, X-ray measurements were performed at different temperatures. The calculations of X-ray results demonstrate a hexagonal columnar packing of the molecules in the mesophase. Observation of the samples by TEM gives information about the size of the compounds as well as direct evidence of the implementation of Fe2O3 nanoparticles into dendrimers. Physical parameters of the magnetic nanoparticles (magnetic moment, effective magnetic anisotropy) have been determined from analyses of the EPR data.

Nanomagnetic Particle-Based Information Processing

Understanding the physics of spintronic devices in the 3-nm size range can pave the way to next-generation energy-efficient information processing devices. To build a spin computer, a layer of 3-nm CoFe 2 O 4 nanoparticles was sandwiched as a central layer into the standard spin-transfer torque magnetic tunneling junction (STT-MTJ) stack. With further focused ion beam (FIB) trimming, a dual-layer junction consisting of one or more nanoparticles separating two CoFeB ferromagnetic layers was turned into a two-terminal spintronic device. The measured room-temperature electron transport through the device showed a staircase effect reminiscent of a single electron transport, which in addition depended on the relative orientations of the magnetic states of the ferromagnetic layers and the high-anisotropy ferrimagnetic nanoparticle. Besides having the staircase steps, the V-I curve indicated switching of the nanoparticles magnetization through the STT effect at currents of above 0.05 uA. The magnetoresistance (MR) curve of this device with the magnetic field applied perpendicular to the junction had an anomalous oscillatory field dependence in a relatively low field range of below 100 Oe.

Design strategies for shape-controlled magnetic iron oxide nanoparticles.

Ferrimagnetic iron oxide nanoparticles (magnetite or maghemite) have been the subject of an intense research, not only for fundamental research but also for their potentiality in a widespread number of practical applications. Most of these studies were focused on nanoparticles with spherical morphology but recently there is an emerging interest on anisometric nanoparticles. This review is focused on the synthesis routes for the production of uniform anisometric magnetite/maghemite nanoparticles with different morphologies like cubes, rods, disks, flowers and many others, such as hollow spheres, worms, stars or tetrapods. We critically analyzed those procedures, detected the key parameters governing the production of these nanoparticles with particular emphasis in the role of the ligands in the final nanoparticle morphology. The main structural and magnetic features as well as the nanotoxicity as a function of the nanoparticle morphology are also described. Finally, the impact of each morphology on the different biomedical applications (hyperthermia, magnetic resonance imaging and drug delivery) are analysed in detail. We would like to dedicate this work to Professor Carlos J. Serna, Instituto de Ciencia de Materiales de Madrid, ICMM/CSIC, for his outstanding contribution in the field of monodispersed colloids and iron oxide nanoparticles. We would like to express our gratitude for all these years of support and inspiration on the occasion of his retirement.

Magnetoelectric coupling in iron oxide nanoparticle—barium titanate composites

Ferrimagnetic iron oxide nanoparticle monolayers on top of ferroelectric BaTiO3 substrates were prepared and a magnetoelectric coupling effect was observed. We employed hereby a magnetoelectric AC susceptibility setup as modification of a commercial superconducting quantum interference device magnetometer. The magnetoelectric coefficient shows two jumps at the BaTiO3 phase transition temperatures. Moreover, the magnetic depth profile of the nanoparticle monolayer was probed by polarized neutron reflectivity. The data recorded at various electric field values show that the electric field is able to alter the magnetism of the nanoparticle monolayer by a strain mediated magnetoelectric coupling effect.

Fabrication of magneto-optical waveguides inside transparent silica xerogels containing ferrimagnetic Fe3O4 nanoparticles.

Magneto-optical waveguides with a refractive-index change were successfully fabricated inside silica xerogels containing ferrimagnetic Fe3O4 nanoparticles (NPs) using femtosecond laser processing. Aminopropyltriethoxysilane-derived xerogels were prepared via a sol-gel process with aqueous solutions of Fe3O4 NPs synthesized by coprecipitation. The mass/volume concentration of Fe3O4 NPs in the xerogels was determined by comparing the absorbance of the xerogel with that of an aqueous solution of Fe3O4 NPs. We evaluated Faraday rotation angles for light propagating through waveguide structures in xerogels containing Fe3O4 NPs at mass/volume concentrations of 0.087 and 0.148 mg/cm3 at a wavelength of 488 nm. Ferrimagnetic saturation of the Faraday rotation angle was observed, which is consistent with the magnetization curves measured at room temperature. Magneto-optical waveguides can potentially be used to produce micro-sized Faraday devices, such as optical isolators, high-density magnetic recording devices, and optical sensors, which can be integrated with optical and electronic hybrid circuits.

The effect of rotating magnetic field on bioethanol production by yeast strain modified by ferrimagnetic nanoparticles

Abstract Bioethanol is a promising liquid biofuel, which can be produced from the wide range of biomass feedstock by the fermentation process with the Saccharomyces cerevisiae yeast. The application of the rotating magnetic field (RMF) is one of the possibilities to increase the efficiency of the process. Therefore, the magnetically-assisted bioreactor equipped with RMF generator was used to perform the ethanol fermentation process with the sugar-rich medium. Moreover, the yeast cells were modified by addition of Fe3O4 nanoparticles. The obtained data suggested that the stimulation of applied cells with RMF did increase the proliferation and the ethanol production process. Furthermore, the calculated maximum specific growth rate and the productivity coefficient showed RMF positive effect on this magnetically-assisted bioprocess. The stimulation was found as ruled by field frequency (connected with magnetic induction of RMF) and it was revealed that the process productivity was higher for experiments with modified cells and the growth rate was higher for the process without the addition of Fe3O4 nanoparticles.

Pulsed Field-Induced Magnetization Switching in Antiferromagnetic Ferrihydrite Nanoparticles

The dynamic magnetization switching of ferrihydrite nanoparticles has been investigated by a pulsed magnetometer technique in maximum fields Hmax of up to 130 kOe with pulse lengths of 4, 8, and 16 ms. Ferrihydrite exhibits antiferromagnetic ordering and defects cause the uncompensated magnetic moment in nanoparticles; therefore, the behavior typical of magnetic nanoparticles is observed. The dynamic hysteresis loops measured under the above-mentioned conditions show that the use of pulsed fields significantly broadens the temperature region of existence of the magnetic hysteresis and the coercivity can be governed by varying the maximum field and pulse length. This behavior is resulted from the relaxation effects typical of conventional ferro- and ferrimagnetic nanoparticles and the features typical of antiferromagnetic nanoparticles.

Giant Exchange‐Bias in Polyol‐Made CoFe2O4‐CoO Core–Shell Like Nanoparticles

AbstractCobalt ferrite ferrimagnetic nanoparticles (NPs) are prepared and used in this work as seeds to grow a thin antiferromagnetic poly‐ and nanocrystalline CoO shell. The major purpose is to study systematically the characteristics of the as‐produced powders, making emphasis on their internal crystallographic arrangement and their magnetic properties. 57Fe Mössbauer spectrometry evidences an evolution of the cation distribution among the spinel lattice in the cobalt ferrite core during the core–shell NPs processing. High‐resolution transmission electron microscopy shows a perfect epitaxy between the face‐centered cubic lattices of the spinel core and the rock‐salt shell. Finally, the measurements of 7T‐field‐cooled magnetic hysteresis loops at low temperature (5 K) of the composite particles exhibit a strong exchange bias coupling with an exchange field, µ0HE, of 365 mT and an enhanced coercive field, µ0HC, of 1395 mT. These values are very high compared to those of differently prepared CoO‐based oxide composite NPs and for which a giant exchange‐bias is reported. These features are attributed to the favorable material processing conditions offered by the polyol process in terms of crystalline quality, particularly at the interfaces, and for the pinning action exerted by the CoO phase on the magnetization of the CoFe2O4 phase.

Structural, magnetic, and electrical properties of sol–gel derived cobalt ferrite nanoparticles

This work reports the synthesis and studies of semi-soft ferrimagnetic CoFe2O4 nanoparticles using sol–gel method. The X-ray diffraction patterns confirm the formation of cubic spinel CoFe2O4 nanoparticles. The average crystallite size was found from XRD data is about 30 nm. The high resolution transmission electron microscopy analysis shows that nanoparticles are highly crystalline. The magnetic properties reveal that the particles are ferrimagnetically ordered soft magnetic materials with coercive field of 620 Oe and saturation magnetization Ms = 60 emug− 1. The higher value of saturation magnetization is due to the ordered single-domains magnetic nanoparticles and lower magnitude of coercivity is attributed to the decrease of interparticle interactions and magneto-elastic anisotropy. The value of remanence ratio R < 0.5 is responsible for magnetostatic interactions of the particles. The nanoparticles possess low values of dielectric constant which decreased with increasing frequency. The low dielectric constant makes the nanoparticles as a promising candidate for high frequency magnetic devices.