Significant Magnetic Responses Research Articles

Direct continuous synthesis of macroRAFT-grafted Fe3O4 nanoclusters for the preparation of magnetic nanocomposites

A new method for synthesizing magnetic nanocomposite latex particles with a significant magnetic response and high coating rate is reported herein. Based on a micro-flow platform, Fe3O4 nanoclusters grafted with macroRAFT agents were continuously synthesized within 90 s. The obtained clusters present high mono-dispersity, narrow size distribution, and excellent saturation magnetization. Moreover, the macroRAFT polymer chains grafted on the surface of the nanoclusters can be reactivated for polymerizing hydrophobic monomers without using any surfactant, to achieve the coating of magnetic particles. The resulting polymer shell can protect the magnetic core and maintain a substantial magnetic response. Furthermore, by optimising the reaction conditions, the encapsulation efficiency can be significantly improved for the efficient preparation of magnetic nanocomposites.

Novel Ferritic Stainless Steel with Advanced Mechanical Properties and Significant Magnetic Responses Processed by Selective Laser Melting

Novel Ferritic Stainless Steel with Advanced Mechanical Properties and Significant Magnetic Responses Processed by Selective Laser Melting

Magnetic Characterization of Selective Laser-Melted Saf 2507 Duplex Stainless Steel

Selective laser melting (SLM) is disruptive in terms of the sensitive balance between constituent phases of the biphasic duplex stainless steel material options. While adversely affecting the mechanical and corrosion properties, the predominantly ferritic structures resulting from the high thermal gradients were also noted to impart significant magnetic responses. Scientific attention is essential for ascertaining the material-process-magnetic response relationships to establish the underlying principles and critical responses. This is attempted here through magnetic characterization based on results from saturation hysteresis loops and evaluation of austenite–ferrite ratios allowing for identification of the structure–magnetic property relationships. Overall, the experimental results indicated strong process–property relationships, whereas the magnetic saturation levels of SLM samples are much higher compared with the wrought counterparts.

Combinatorial Fe–Co thin film magnetic structures obtained by thermionic vacuum arc method

Magnetoresistive Fe–Co based thin film structures were produced using thermionic vacuum arc method. The purpose of this work was to obtain significant magnetic response on different granular combinatorial structures. The Giant Magnetoresistive (GMR) and combination between GMR and Tunneling Magnetoresistive (TMR) properties of the thin film structures were the aim of the work. The proposed method in order to obtain the desired granular structures is based on electron beam emitted by an externally heated cathode, accelerated by a high anodic potential.The work consisted in preparing two sets of samples, first being a combination between Fe–Co as magnetic materials embedded in a Cu matrix, with a total thickness of 200nm. The second structure was a combination between Fe–Co (50%–50%) alloy, embedded in a matrix of Cu combined with MgO with a thickness of 200nm. Both sets of samples were obtained by three simultaneous types of discharges. Because of the substrate positioning in respect with the three anode–cathode systems, different material concentrations were obtained, confirmed by Energy Dispersive Spectroscopy (EDS) measurement results. Structural and morphological properties were investigated using Scanning Electron Microscopy; Atomic Force Microscopy and EDS. Electrical properties of the obtained samples were studied using the 4 point measurement method. The magnetic properties were first studied using a non-destructive optical method called MOKE (Magneto-Optical Kerr Effect). Electrical resistance behavior of the granular type structures was studied for different values of the magnetic field, up to 0.3T, at different values of the sample temperature. The magnetoresistive effect obtained for the two sets of samples varied from 1.5% to 81% in respect with the substrate positioning and sample temperature for a constant magnetic field.

Broadband spectroscopy of the electromagnetic properties of aqueous ferrofluids for biomedical applications

This paper presents the results of a broadband spectroscopy study, over the frequency range 1 MHz–2 GHz, of the electromagnetic properties of a ferrofluid consisting of magnetite nanoparticles, with a mean magnetic size of 10 nm, dispersed in water. An innovative measurement approach and apparatus, allowing an accurate determination of the permeability, even in presence of a large permittivity, have been developed to characterize the suspension. The results obtained show a significant magnetic response over the whole analyzed frequency range, with a good agreement with the theoretical models describing the magnetization dynamics of these systems. Moreover, a strong dielectric response has been detected, which is in satisfactory agreement with the models developed to describe the dielectric behavior of charged nanoparticles suspended in aqueous solution. This result implies that measurement techniques able to determine both the permittivity and permeability become mandatory for a reliable determination of the magnetic properties of aqueous ferrofluids. The accuracy of the determined permeability spectrum is estimated to be of the order of few percent, so these results provide a reliable experimental basis to estimate how fruitful the use of magnetic nanoparticles can be in relevant biomedical applications.

Modeling nonlinear effects in 2D optical metamagnetics

We use a previously developed approach to study stationary TM-type waves propagating in two-dimensional nonlinear optical metamagnetics, pertinent to a separate class of metamaterials with a significant magnetic response at optical frequencies. Since an implicit equation for the nonlinear dielectric functions should be resolved, the TM-type waves within the standard E-field formulations of nonlinear optics cannot be treated using a purely scalar H-field context. We use the optically controlled isotropic Kerr-type nonlinearity to illustrate the proposed approach, while analyzing the performance of an optically tunable metamagnetic. The simulation results prove the expected tuning of the magnetic resonance within a 100-nm band around the center wavelength of 1.55 μm.

Temporal structure of the apparent motion perception: a magnetoencephalographic study

Humans perceive motion when numerous small dots pattern is followed by one of the same pattern but with all the dots shifted a little in one direction. When the amount of shift exceeds a level humans no more perceive motion even though physical visual information does not change. Using this stimulus, we addressed to elucidate the temporal structure of the neural activity related to this apparent motion perception. The magnetic responses to the random-dot patterns with various amounts of shift were measured while the subjects were performing a direction discrimination task. A significant magnetic response amplitude change occurred with three distinct peaks when the response inducing apparent motion was compared with those inducing no motion without change in the response latencies. The major difference occurred at about 110, 140, 210 ms after the stimulus onset. The response origin was always within the occipitotemporal area. The results indicate that the neural activity for the perception of apparent motion can be measured by MEG that occur at least 110 ms after the stimulus onset possibly in the human MT+. Three distinct peaks in the response difference may represent the sequential multiple neural process proposed theoretically though further study is necessary to prove.