Superconducting Quantum Interference Device Magnetometry Research Articles

Toxicity and magnetometry evaluation of the uptake of core-shell maghemite-silica nanoparticles by neuroblastoma cells.

Nanoparticle uptake by cells is a key parameter in their performance in biomedical applications. However, the use of quantitative, non-destructive techniques to obtain the amount of nanoparticles internalized by cells is still uncommon. We have studied the cellular uptake and the toxicity of core-shell maghemite-silica magnetic nanoparticles (MNPs), with a core diameter of 9 nm and a shell thickness of 3 nm. The internalization of the nanoparticles by mouse neuroblastoma 2a cells was evaluated by sensitive and non-destructive Superconducting Quantum Interference Device (SQUID) magnetometry and corroborated by graphite furnace atomic absorption spectroscopy. We were thus able to study the toxicity of the nanoparticles for well-quantified MNP uptake in terms of nanoparticle density within the cell. No significant variation in cell viability or growth rate was detected for any tested exposure. Yet, an increase in both the amount of mitochondrial superoxide and in the lysosomal activity was detected for the highest concentration (100 μg ml-1) and incubation time (24 h), suggesting the onset of a disruption in ROS homeostasis, which may lead to an impairment in antioxidant responses. Our results validate SQUID magnetometry as a sensitive technique to quantify MNP uptake and demonstrate the non-toxic nature of these core-shell MNPs under our culture conditions.

Removal of methyl orange textile dye using magnetic chitosan microspheres adsorbent

Abstract Industrial textile wastewater contains high levels of dyes, which are potentially harmful to aquatic ecosystems by inhibiting sunlight penetration for photosynthesis activities. Adsorption is a simple method for pollutant removal for water treatment. Magnetic Chitosan Microspheres (MCM) has been developed as a natural adsorbent for dye removal. This study aimed to compare the properties of the raw adsorbent and after adsorption by FT-IR, BET, DLS, and SQUID Magnetometry. The adsorption behaviours were investigated by the influence of pH, contact time, and initial concentration on Methyl Orange removal. The result was MCM could eliminate MO until 93.60% at pH 7 with C0 100 mg L−1 in 5 min with an adsorption capacity of 187.21 mg g−1. Adsorption processes were also studied through the isotherm and kinetic. The isotherm showed a closer fit to the Langmuir model than the Freundlich model. The kinetic result showed the PSO model was more suitable than PFO. The research data using MCM for adsorption demonstrated excellent adsorption capability in terms of dye removal percentage and high adsorption capacity. Therefore, this material could be an effective adsorbent for the treatment of dye-containing wastewater.

Trans Ligand Determines the Stability of Paramagnetic Manganese(II) Hydrides of the Type trans-[MnH(L)(dmpe)2]+ Where L is PMe3, C2H4, or CO.

Paramagnetic metal hydride (PMH) complexes play important roles in catalytic applications and bioinorganic chemistry. 3d PMH chemistry has largely focused on Ti, Mn, Fe, and Co. Various MnII PMHs have been proposed as intermediates in catalysis, but isolated MnII PMHs are limited to dimeric high-spin MnII structures with bridging hydrides. In this paper, a series of the first low-spin monomeric MnII PMH complexes are generated by chemical oxidation of their MnI analogues. This series is of the type trans-[MnH(L)(dmpe)2]+/0 where the trans ligand L is PMe3, C2H4, or CO [dmpe is 1,2-bis(dimethylphosphino)ethane], and the thermal stability of the MnII hydride complexes was found to be strongly dependent on the identity of the trans ligand. When L is PMe3, the complex is the first example of an isolated monomeric MnII hydride complex. In contrast, when L is C2H4 or CO, the complexes are only stable at low temperatures; upon warming to room temperature, the former decomposed to afford [Mn(dmpe)3]+, accompanied by ethane and ethylene, whereas the latter eliminated H2, generating [Mn(MeCN)(CO)(dmpe)2]+ or a mixture of products including [Mn(κ1-PF6)(CO)(dmpe)2], depending on the reaction conditions. All PMHs were characterized by low-temperature electron paramagnetic resonance (EPR) spectroscopy, and stable [MnH(PMe3)(dmpe)2]+ was further characterized by UV-vis and IR spectroscopy, Superconducting Quantum Interference Device magnetometry, and single-crystal X-ray diffraction. Noteworthy spectral properties are the significant EPR superhyperfine coupling to the hydride (∼85 MHz) and an increase (+33 cm-1) in the Mn-H IR stretch upon oxidation. Density functional theory calculations were also employed to gain insights into the acidity and bond strengths of the complexes. MnII-H bond dissociation free energies are estimated to decrease in the series of complexes from 60 (L = PMe3) to 47 kcal/mol (L = CO).

Magnetic properties of the mononuclear iron (III) complexes with biphenyl‐disubstituted Schiff base ligand: EPR and SQUID study

The magnetic features of the mononuclear iron (III) complexes [Fe(L)2]+X−with tridentate Schiff base ligands [where L is 4‐(4‐diphenylcarboxy)‐2′‐oxysalicylidene‐N′‐ethylene‐N‐ethylene‐2′‐amine‐(carboxy‐4‐diphenyl) and X− = Cl−(1), PF6−(2) and NO3−(3) counter‐ions] have been studied by electron paramagnetic resonance (EPR) spectroscopy, SQUID (superconducting quantum interference device) magnetometry (solid), and Evans1H nuclear magnetic resonance method (solution). EPR established that compounds (1) and (2) consist of two types high‐spin (HS, S = 5/2) centers with weak distorted and strong low‐symmetry octahedral crystal fields. The signals from low‐spin centers (LS, S = 1/2) of Fe (III) are observed in the spectra of compounds2and3. SQUID revealed permanent HS behavior in (1) and mixed LS + HS in (2), (3) in wide temperature range, while solution method—only HS. Magnetic measurements allowed to estimate part of HS and LS fractions and detected antiferromagnetic exchange interactions between the neighboring Fe (III) ions in complexes.“

Relationship between the Formation of Magnetic Clusters and Hexagonal Phase of Gold Matrix in AuxFe1-x Nanophase Thin Films.

AuxFe1−x nanophase thin films of different compositions and thicknesses were prepared by co-deposition magnetron sputtering. Complex morpho-structural and magnetic investigations of the films were performed by X-ray Diffraction, cross-section Transmission Electron Microscopy, Selected Area Electron Diffraction, Magneto Optical Kerr Effect, Superconducting Quantum Interference Device magnetometry and Conversion Electron Mössbauer Spectroscopy. It was proven that depending on the preparation conditions, different configurations of defect α-Fe magnetic clusters, i.e., randomly distributed or auto-assembled in lamellar or filiform configurations, can be formed in the Au matrix. A close relationship between the Fe clustering process and the type of the crystalline structure of the Au matrix was underlined, with the stabilization of a hexagonal phase at a composition close to 70 at. % of Au and at optimal thickness. Due to different types of inter-cluster magnetic interactions and spin anisotropies, different types of magnetic order from 2D Ising type to 3D Heisenberg type, as well as superparamagnetic behavior of non-interacting Fe clusters of similar average size, were evidenced.

Uranium(III)–Phosphorus(III) Synergistic Activation of White Phosphorus and Arsenic

Uranium(III)–Phosphorus(III) Synergistic Activation of White Phosphorus and Arsenic

Magneto-optical properties of borophosphate glasses co-doped with [formula omitted] and [formula omitted]ions

Glasses from lithium-aluminum-zinc-boron-phosphorous oxide system co-doped with terbium (Tb3+) and dysprosium (Dy3+) oxides were studied for magneto-optical applications in lasers. The Fourier Transform Infrared and Raman Spectroscopy complementary analysis suggested the depolymerization of the boro-phosphate glass network by adding and increasing the rare-earth (RE) oxide content. Main UV–vis absorption maxima of Tb and Dy ions were identified at 348 and 1266 nm. Spectroscopic ellipsometry indicated a maximum refractive index of 1.56, at 400 nm, for the highest RE content. The Verdet constant amplified by increasing the RE content, reaching for the 9 mol% RE co-doped sample a value of -0.075 min/Oe/cm at 630 nm. The Faraday rotation angle was additionally confirmed by using a Faraday Cell Device, being also related to the specific paramagnetic behavior evidenced by Superconducting Quantum Interference Device magnetometry. The magneto-optical properties recommend such vitreous co-doped materials for magneto-optical devices.

Core Size and Interface Impact on the Exchange Bias of Cobalt/Cobalt Oxide Nanostructures

Two series of Co/Co-oxide nanostructures have been synthesized by the co-precipitation method followed by different reduction and oxidation processes in an attempt to optimize their exchange bias (EB) properties. The samples are characterized by X-ray diffraction, scanning and transmission electron microscopy, and SQUID (superconducting quantum interference device) magnetometry. The two series differ with respect to their average Co core grain sizes: in one (the l-series), the size is ≈100 nm, and in the other (the s-series, obtained using lower synthesis temperatures than the l-series), it is ≈10 nm. In the l-series, progressive oxidation yields an increase in the EB field together with a reduction in Co core size. In contrast, progressive oxidation in the s-series results in growth of the Co-oxide fraction at the expense of the Co core upon oxidation, which is accompanied by a decrease in the EB effect that is attributed to an ordering of the ferromagnetic–antiferromagnetic interface and therefore a reduction of uncompensated spins density. These results illustrate how the interface details become relevant only for small enough ferromagnetic cores.

Magnetic Phase Coexistence and Hard-Soft Exchange Coupling in FePt Nanocomposite Magnets.

With the aim of demonstrating phase coexistence of two magnetic phases in an intermediate annealing regime and obtaining highly coercive FePt nanocomposite magnets, two alloys of slightly off-equiatomic composition of a binary Fe-Pt system were prepared by dynamic rotation switching and ball milling. The alloys, with a composition Fe53Pt47 and Fe55Pt45, were subsequently annealed at 400 °C and 550 °C and structurally and magnetically characterized by means of X-ray diffraction, 57Fe Mössbauer spectrometry and Superconducting Quantum Interference Device (SQUID) magnetometry measurements. Gradual disorder–order phase transformation and temperature-dependent evolution of the phase structure were monitored using X-ray diffraction of synchrotron radiation. It was shown that for annealing temperatures as low as 400 °C, a predominant, highly ordered L10 phase is formed in both alloys, coexisting with a cubic L12 soft magnetic FePt phase. The coexistence of the two phases is evidenced through all the investigating techniques that we employed. SQUID magnetometry hysteresis loops of samples annealed at 400 °C exhibit inflection points that witness the coexistence of the soft and hard magnetic phases and high values of coercivity and remanence are obtained. For the samples annealed at 500 °C, the hysteresis loops are continuous, without inflection points, witnessing complete exchange coupling of the hard and soft magnetic phases and further enhancement of the coercive field. Maximum energy products comparable with values of current permanent magnets are found for both samples for annealing temperatures as low as 500 °C. These findings demonstrate an interesting method to obtain rare earth-free permanent nanocomposite magnets with hard–soft exchange-coupled magnetic phases.

Origin of the magnetic properties of Fe-implanted 4H-SiC semiconductor

p-doped 4H-SiC substrates were implanted with 57Fe ions at energies ranging from 30 to 160 keV and subjected to a rapid thermal annealing in order to produce a homogeneous Fe concentration inside a 100 nm-thick region in the semiconducting SiC material. Using 57Fe Conversion Electron Mössbauer Spectrometry and Superconducting Quantum Interference Device magnetometry, we give evidence that the ferromagnetism obtained in SiC implanted with a 57Fe atoms concentration close to 2% is not only due to the formation of some Fe–Si magnetic nanoparticles but also originates from magnetic Fe atoms diluted in the matrix of the semiconductor. So, values of Fe atoms magnetizations contained in nanoparticles and Fe atoms diluted in the matrix and the Curie temperatures associated with the nanoparticles and to the matrix have been determined.

Nanowire crystals of tantalum nitride grown in ammonium halide fluxes at high pressures

Nanowire crystals of a tantalum nitride phase have been grown from epsilon-tantalum nitride and ammonium halide precursors at high pressures exceeding several gigapascals. Synchrotron x-ray diffraction and Transmission Electron Microscopy (TEM) observations revealed that they had crystallized in an unreported hexagonal structure with lattice parameters of a = 3.050(1) Å and c = 2.909(2) Å. The one-dimensional growth orientation was along the crystallographic [001] direction. Scanning TEM–EDX elemental analyses showed that the nanowire crystals were composed of tantalum and nitrogen with small amounts of oxygen. The presence of the melted ammonium halides combined with supercritical ammonia acting as a reactive flux at high pressure and temperature played a significant role in the nanowire crystal growth. Raman spectroscopy performed on several single crystal nanowires pointed toward metallic properties, and the temperature dependence of the magnetization measured by Superconducting Quantum Interference Device magnetometry suggested a superconducting transition about 6.2 K. The analysis of the compression behavior revealed an incompressible nature, and the bulk modulus was determined to be 363(6) GPa.

To the Intrinsic Magnetism of the Bi108Sn0.02Sb0.9Te2S Topological Insulator

Using Electron Spin Resonance spectroscopy together with the Superconducting Quantum Interference Device magnetometry, we found that the intrinsic magnetic moments, originating from the nonmagnetic structural defects of Bi1.08Sn0.02Sb0.9Te2S topological insulator form the superparamagnetic state. It represents an array of nanoscale single domain ferromagnets randomly distributed in the nonmagnetic media. Their net magnetic polarization in the absence of external magnetic field is completely averaged out. Single domain ferromagnetic particles at elevated temperatures behave magnetically in a manner analogous to the Langevin paramagnetism of moment bearing atoms. The main distinction is that the moment of the particle may be 102—103 times the atomic moment.

Development of Ferrite-Based Temperature Sensors for Magnetic Resonance Imaging: A Study of Cu1−xZnxFe2O4

We investigate the use of Cu1-x Zn x Fe2O4 ferrites (0.60 < x < 0.76) as potential sensors for magnetic- resonance-imaging thermometry. Samples are prepared by a standard ceramic technique. Their structural and magnetic properties are determined using x-ray diffraction, scanning electron microscopy, super-conducting quantum-interference device magnetometry, and Mossbauer and 3-T nuclear-magnetic-resonance spectroscopies. We use the mass magnetization of powdered ferrites and transverse relaxivity r*2 of water protons in Ringer's-solution-based agar gels with embedded micron-sized particles to determine the best composition for magnetic-resonance-imaging (MRI) temperature sensors in the (280-323)-K range. A preclinical 3-T MRI scanner is employed to acquire T*2 weighted temperature-dependent images. The brightness of the MRI images is cross-correlated with the temperature of the phantoms, which allows for a temperature determination with approximately 1°C accuracy. We determine that the composition of 0.65 < x < 0.70 is the most suitable for MRI thermometry near human body temperature.

Calibration standard of body tissue with magnetic nanocomposites for MRI and X-ray imaging

We present a first study of a long-term phantom for Magnetic Resonance Imaging (MRI) and X-ray imaging of biological tissues with magnetic nanocomposites (MNC) suitable for 3-dimensional and quantitative imaging of tissues after, e.g. magnetically assisted cancer treatments.We performed a cross-calibration of X-ray microcomputed tomography (XµCT) and MRI with a joint calibration standard for both imaging techniques. For this, we have designed a phantom for MRI and X-ray computed tomography which represents biological tissue enriched with MNC.The developed phantoms consist of an elastomer with different concentrations of multi-core MNC. The matrix material is a synthetic thermoplastic gel, PermaGel (PG).The developed phantoms have been analyzed with Nuclear Magnetic Resonance (NMR) Relaxometry (Bruker minispec mq 60) at 1.4T to obtain R2 transverse relaxation rates, with SQUID (Superconducting QUantum Interference Device) magnetometry and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to verify the magnetite concentration, and with XµCT and 9.4T MRI to visualize the phantoms 3-dimensionally and also to obtain T2 relaxation times. A specification of a sensitivity range is determined for standard imaging techniques X-ray computed tomography (XCT) and MRI as well as with NMR.These novel phantoms show a long-term stability over several months up to years. It was possible to suspend a particular MNC within the PG reaching a concentration range from 0mg/ml to 6.914mg/ml.The R2 relaxation rates from 1.4T NMR-relaxometry show a clear connection (R2=0.994) with MNC concentrations between 0mg/ml and 4.5mg/ml. The MRI experiments have shown a linear correlation of R2 relaxation and MNC concentrations as well but in a range between MNC concentrations of 0mg/ml and 1.435mg/ml.It could be shown that XµCT displays best moderate and high MNC concentrations. The sensitivity range for this particular XµCT apparatus yields from 0.569mg/ml to 6.914mg/ml.The cross-calibration has defined a shared sensitivity range of XµCT, 1.4T NMR relaxometer minispec, and 9.4T MRI. The shared sensitivity range for the measuring method (NMR relaxometry) and the imaging modalities (XµCT and MRI) is from 0.569mg/ml, limited by XµCT, and 1.435mg/ml, limited by MRI.The presented phantoms have been found to be suitable to act as a body tissue substitute for XCT imaging as well as an acceptable T2 phantom of biological tissue enriched with magnetic nanoparticles for MRI.

The local structure and ferromagnetism in Fe-implanted SrTiO3 single crystals

We report a connection between the local structure of low-level Fe impurities and vacancies as the cause of ferromagnetic behavior observed in strontium titanate single crystals (STO), which were implanted with Fe and Si ions at different doses then annealed in oxygen. The effects of Fe doping and post-implantation annealing of STO were studied by X-ray Absorption Near Edge Structure (XANES) spectroscopy and Superconducting Quantum Interference Device magnetometry. XANES spectra for Fe and Ti K- and L-edge reveal the changes in the local environment of Fe and Ti following the implantation and annealing steps. The annealing in oxygen atmosphere partially healed implantation damages and changed the oxidation state of the implanted iron from metallic Fe0 to Fe2+/Fe3+ oxide. The STO single crystals were weak ferromagnets prior to implantation. The maximum saturation moment was obtained after our highest implantation dose of 2 × 1016 Fe atom/cm2, which could be correlated with the metallic Fe0 phases in addition to the presence of O/Ti vacancies. After recrystallization annealing, the ferromagnetic response disappears. Iron oxide phases with Fe2+ and Fe3+ corresponding to this regime were identified and confirmed by calculations using Real Space Multiple Scattering program (FEFF9).

Characterization of Nickel Ions in Nickel‐Doped Yttria‐Stabilized Zirconia

The distribution of Ni2+ ions in NiO‐doped 10YSZ powder is examined with Superconducting Quantum Interference Device magnetometry, a technique that is able to distinguish between randomly distributed Ni2+ ions in solid solution and ordered Ni2+ ions within NiO with high precision. Very high purity powders containing 0.01, 0.1, 0.5, and 1.0 mol% NiO in 10YSZ (all levels below the solid solubility limit of NiO in 10YSZ) were made from acetate precursors and a modified EDTA (ethylenediaminetetraacetic acid)‐citrate synthesis method. The powders were calcined in air at either 873 or 1273 K. The 873 K calcination leads to single phase YSZ particles about 10 nm in diameter, and almost all of the NiO dopant exists in complete solid solution. The 1273 K calcination leads to a larger YSZ particle size (55–95 nm), and also to the formation and/or growth of NiO particles, the amount of which depends on the length of time of calcination. Upon sintering the powders in air (1773 K, 1 h), the NiO dissolves back into 10YSZ. The results demonstrate that particle growth during calcination leads to the exsolution of Ni2+ ions to form NiO. This has important implications for the synthesis of NiO‐doped 10YSZ from chemical precursors.

Nanoincorporation of iron oxides into carrageenan gels and magnetometric and morphological characterizations of the composite products

Carrageenan-based magnetic composites were prepared via in situ synthesis of iron oxides in a gelatinous network of the polysaccharide. The repeatable synthesis process involved three steps: immersion into ferrous salt (FeCl2) solution, alkali treatment in sodium hydroxide solution and oxidation with hydrogen peroxide, successively performed with τ- or κ-carrageenan hydrogels as the starting material. Field emission scanning electron microscope observations, X-ray diffractometry and superconducting quantum interference device (SQUID) magnetometry were carried out for the freeze-dried composites. Feroxyhite and magnetite and/or maghemite particles were produced after one cycle and multicycles of the in situ process, respectively, with a size less than several tens of nanometers, and were distributed throughout the inside as well as on the surface of numerous fibrillar entities constituting the carrageenan matrix. Nearly all the composite products explored displayed a superparamagnetic (SPM) property at 298 K; the estimated saturation magnetization (Ms) increased with increasing concentrations of FeCl2 in the gel immersion step and with repetition of the standardized process of iron oxide synthesis. By repeating the synthesis cycle 3–4 times, a composite of practically high Ms reaching ∼25 emu (g sample)−1 was easily obtained without impairing the SPM character. Insight was provided into the evolution mechanism of the oxidation state and dimensional distribution of the cyclically loaded iron oxide nanoparticles through comparison with another composite series obtained by a co-precipitation method with a 1:2 mixture of ferrous/ferric salts. Carrageenan-based magnetic composites were prepared via in situ synthesis of iron oxides in a gelatinous network of the polysaccharide. Magnetic properties and morphology were characterized by SQUID magnetometry, X-ray diffractometry and electron miscroscopy. By operation of 3–4 cycles of the standard synthesis route, a carrageenan composite imparting a high value of saturation magnetization (∼25 emu (g sample)−1) was easily realized while the superparamagnetic property at room temperature was maintained. Insight was provided into the evolution mechanism in oxidation state and dimensional distribution of the cyclically loaded iron oxide nanoparticles.

An Endohedral Single-Molecule Magnet with Long Relaxation Times: DySc2N@C80

The magnetism of DySc(2)N@C(80) endofullerene was studied with X-ray magnetic circular dichroism (XMCD) and a magnetometer with a superconducting quantum interference device (SQUID) down to temperatures of 2 K and in fields up to 7 T. XMCD shows hysteresis of the 4f spin and orbital moment in Dy(III) ions. SQUID magnetometry indicates hysteresis below 6 K, while thermal and nonthermal relaxation is observed. Dilution of DySc(2)N@C(80) samples with C(60) increases the zero-field 4f electron relaxation time at 2 K to several hours.

Structural and magnetic characterization of superparamagnetic iron platinum nanoparticle contrast agents for magnetic resonance imaging.

The authors report the synthesis, from simple salts, and the physical characterization of superparamagnetic iron platinum nanoparticles (SIPPs) suitable for use as contrast agents in magnetic resonance imaging. The properties of these particles were determined by means of transmission electron microscopy (TEM), thermogravimetric analysis, inductively coupled plasma-optical emission spectroscopy (ICP-OES), superconducting quantum interference device (SQUID) magnetometry, and nuclear magnetic resonance relaxivity at 4.7 T. TEM showed that the diameters of the particles ranged from 9.3 to 10 nm, depending on the mole ratio of iron to platinum precursors, and on the concentration of octadecylamine (ODA) used in their preparation. The iron to platinum stoichiometry determined by ICP-OES varied from 1.4:1 to 3.7:1 and was similarly dependent on the initial mole ratios of iron and platinum salts, as well as on the concentration of ODA in the reaction. SQUID magnetometry showed that the SIPPs were superparamagnetic and had magnetic moments that increased with increasing iron content from 62 to 72 A·m2/kg Fe. The measured relaxivities of the SIPPs at 4.7 T were higher than commercially available superparamagnetic iron oxide nanoparticles, suggesting that these particles may be superior contrast agents in T2-weighted magnetic resonance imaging.

Influence of processing methodology on the structural and magnetic behavior of MgFe2O4 nanopowders

Three different wet chemistry routes namely reverse micelle, citrate gel and co-precipitation methods were used to synthesize magnesium ferrite nanopowders. The synthesized spinel was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman spectroscopy techniques, transmission electron microscopy (TEM) and Superconducting Quantum Interference Device magnetometry (SQUID). The gel combustion method yield comparatively pure crystalline phase of MgFe2O4 and relatively higher saturation magnetization of 22.7emu/g. The material synthesized using co-precipitation method yield other phases in addition to the targeted phase. The average diameter of nanoparticles obtained from reverse microemulsion route was about 19.6±2nm, and for those obtained from gel combustion and co-precipitation route are highly agglomerated. The reverse micelle process produces fine nanosized particles compared with other methods reported in the literature. Superconducting Quantum Interference Device (SQUID) magnetometer reveals that the ferrite nanopowders obtained from the reverse micelle, gel combustion and co-precipitation route exhibit superparamagnetism. The selection of MgFe2O4 synthesis method largely depends on the targeted applications and desired properties. The results reported in this study are useful for establishing a simple method for the preparation of MgFe2O4 nanopowders.