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The rotation of circular and annular pyrolytic graphite (PG) disks levitating above circular magnet arrays can be used for a novel method of magnetic manipulation, whereas the condition of stable levitation has not been figured out yet. In this article, a method to analyze the diamagnetic forces sustained by levitated PG is proposed to investigate the mechanism of stable levitation. When using this method, the whole PG disk is divided into multiple regions according to the distribution of magnetic field in order to determine the resultant diamagnetic force. With the help of the method, the exclusive levitation height of PG disk was determined, and the relationship between the relative size of circular and annular disks to magnet and its ability of stable levitation was clarified. The proposed method is the first one able to investigate the position stability of levitated PG and provides insights into local forces without heavy workload of finete element method (FEM) calculation. The analysis results are verified by the simulation of distribution of potential energy and can be a new way of magnetic manipulation. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles (MNPs) prepared as stable colloidal suspensions dispersed in water have attracted special interest for biological applications. MNPs of iron oxide synthesized by a laser target evaporation (LTE) technique are excellent candidates for biomedical purposes. Magnetic fluid flowing through the blood vessel creates magnetic fields which can be detected by magnetic field sensor. In this work, the finite element method modeling (FEM) was used for calculation of the flow of ferrofluid containing magnetic iron oxide MNPs through a real coronary artery reconstructed from the routine angiography examination of a patient. The main objective of the study is to validate the possibility of the application of magnetic field sensor for the blood vessel geometry evaluation. The contribution of the magnetic susceptibility of MNPs, blood vessel diameter, and particular geometry as well as the orientation of the magnetic field sensor working on the principle of giant magnetoimpedance (GMI) were comparatively analyzed. [ABSTRACT FROM AUTHOR]

We have designed, developed, and evaluated an innovative portable magneto-optical detector (MOD) in which a light beam with variable polarization passes through a fluid sample immersed in a variable magnetic field. The light intensity is measured downstream along the forward scattering direction. The field is turned on and off through the in-and-out motion of nearby permanent magnets. As a result, for sufficiently, magnetically, and optically anisotropic samples, the optical absorption is sensitive to changes in the light polarization. Both detection and characterization applications are, therefore, available. For instance, both the degree of malaria infection and hemozoin crystalline properties can be measured and studied, respectively. We present experimental results for synthetic hemozoin and describe them in terms of the basic physics and chemistry underlying the correlations of the directions of the external magnetic field and the light beam polarization. We connect this work to a commercialized product for malaria detection and compare it with other magneto-optical instruments and methods. We conduct tests of absorption parameters and the electric polarizability tensor, and we discuss the connection to magnetic and electric dipole moments. [ABSTRACT FROM AUTHOR]

This article is devoted to the experimental investigation of the occurrence of the so-called “low-temperature Belov point” $T_{B}$ predicted previously for the mixed rare earth-yttrium iron garnet compounds RE $_{x}Y_{\mathrm {3 - {}}x}$ Fe5O12 possessing or not a magnetic compensation point $T_{\mathrm {comp}}$. Isothermal magnetizations $M_{T}(H)$ of two single crystals of Tb $_{x}Y_{3-x}$ Fe5O12 with rare-earth (RE) = Tb, and $x = 1.98$ , 0.37, were measured in the 4.2–300 K range, using dc magnetic field $H$ up to 100 kOe applied in one or more of the three main crystallographic directions. Anomalies are observed in the region of $T_{B}^{\mathrm {TbIG}} \approx 58$ K, the previous estimated value for TbIG ($x = 3$), in the temperature dependences of the paraprocess susceptibility $\chi _{p}$ , the parameter $\vert b\vert $ of the bH2 term of the quadratic expansion of $M_{T}(H)$ curves, and other pertinent magnetic characteristics. For $x = 1.98$ with $T_{\mathrm {comp}} = 137$ K and when $H$ is applied along $\langle 110\rangle $ , the $\chi _{p}$ - and $\vert b\vert $ -maxima take place close to $T_{B}^{\mathrm {TbIG}}$. The anisotropy of the $\chi _{p}$ -data gives evidence for a spontaneous noncollinear structure around the easy axis of magnetization $\langle 111\rangle $ at 4.2 K. For $x = 0.37$ which has no $T_{\mathrm {comp}}$ point and when $H$ is applied along $\langle 100\rangle $ , the $\chi _{p}$ - and $\vert b\vert $ -maxima are clearly disturbed by the sign anomalies caused by the noncollinear structure instability mechanism due to the crossing of the Tb3+ levels at the critical point $T^{\ast } = 16$ K and by the lower continuous change from the easy axis <100> to a low-symmetry angular phase $\langle $ uuw $\rangle $ due to the first spontaneous spin reorientation phase transition at $T_{\mathrm {SR1}} = 40$ K. When $x$ decreases from 3 to 0.37, it is found that despite different anisotropy effects of the Tb3+ ion, its magnetic moment $m_{\mathrm {Tb}}$ close to $T_{B}^{\mathrm {TbIG}}$ is practically constant (~4.99 in $\mu _{B}$ per Tb3+ ion). [ABSTRACT FROM AUTHOR]

The kinetics of magnetization reversal in a rare-earth-free Mn–Al–C permanent magnet is reported. The $\text{L}1_{0}$ -phase material was prepared using a combination of the melt spinning and spark plasma sintering techniques and characterized with a vibrating sample magnetometer. Magnetic relaxation and susceptibility experiments were performed. Magnetic viscosity, fluctuation field, and activation volume were measured in a wide temperature range. These data were used to analyze the magnetization reversal and temperature dependence of the coercive field. The thermally activated mechanism of the reversed nucleus formation was confirmed for the intermediate temperatures. The role of wall thickness and crystallite size as additional characteristic lengths in magnetic-domain nucleation is discussed. [ABSTRACT FROM AUTHOR]

We examine the structural and magnetic properties of Mg shallow-doped LiMgxFe1−xPO4 (${x} =0.01$ , 0.05, and 0.1) samples synthesized by the conventional solid-state reaction route. Rietveld refinement of the X-ray diffraction patterns shows the crystal structure and bond lengths of LiO6 and Fe(Mg)O6. The Néel temperature (${T} _{\text {N}}$), spin reorientation temperature (${T} _{\text {S}}$), Curie–Weiss temperature, and effective moment decreased owing to the decrease in superexchange interactions with increasing Mg2+ ions. The Mössbauer spectra of samples below ${T} _{\text {N}}$ were fitted with asymmetrical eight absorption lines, whereas above ${T} _{\text {N}}$ were fitted with symmetrical doublet. The change in the value of electric quadrupole splitting and its slop of magnetic susceptibility at ${T} _{\text {S}}$ suggests that spin reorientation related to the orbital angular moment contributes to the magnetic properties by spin–orbit coupling. The value of isomer shift of samples at all temperatures was Fe2+ ion states and it decreased with increasing Mg2+ ion owing to decrease in charge density at the Fe nucleus due to the presence of Mg2+ ions on the FeO6 site. [ABSTRACT FROM AUTHOR]

This article presents a straightforward approach for determination of numerical values of nonlinear susceptibilities of soft magnetic ferrites. It is shown that numerical values of susceptibilities can be calculated from the measured amplitudes of harmonics in the output voltage of ferrite core transformer. For this purpose, useful expressions for the susceptibilities are derived and as example, numerical values of the largest nonlinear susceptibilities those of the third and fifth orders are calculated. Additionally, errors of the measured susceptibilities also are determined. Based on the expressions obtained, the analysis of phase shifts between components of flux density on different frequencies and the magnetic field strength also is performed. The comparison of the calculated and measured output voltage waveforms allows concluding that in the frequency range where losses are small and can be neglected, the susceptibility of the third order is negative but that of the fifth order is positive. [ABSTRACT FROM AUTHOR]

The magnetic and optical properties of suspension of ferrofluid (FF)-based spherical Fe3O4 magnetic nanoparticles (MNPs) in E7 nematic liquid crystal (NLC) matrix have been investigated experimentally in an isotropic phase. The ferronematic liquid crystal (FNLC) mixture exhibits a uniform molecular interaction under an externally applied magnetic field as low as 2 kOe. While the pure NLC shows the expected positive birefringence behavior, the FNLC mixture shows an improvement in tunability with mainly a negative birefringence behavior. The magnetic measurements of samples, including the magnetization curve, hysteresis loop, and pertinent parameters, are carried out using a vibrating sample magnetometer (VSM). The optical properties of samples within the visible spectral range of 380–900 nm are investigated using spectroscopic ellipsometer (SE) device. The results and analysis of magnetic measurements using VSM device show initial magnetic susceptibility of $2.03\times 10^{-6}$ , $8.25\times 10^{-5}$ , $9.85\times 10^{-4}$ , and $3.38\times 10^{-2}$ for FLC0, FLC1, FLC2, and FLC3 samples, respectively. The analysis of SE data shows ordinary and extraordinary refractive indices $n_{\mathrm {o}}$ and $n_{\mathrm {e}}$ of FNLCs samples from 1.85 to 1.67 and from 1.73 to 1.40, respectively. [ABSTRACT FROM AUTHOR]

We investigate some critical phenomena of a Ising ferrimagnetic system on a square lattice with spins $Q=\pm 7/2, \pm 5/2, \pm 3/2$ , and ±1/2 in a $B$ sublattice and spins $S=\pm 5/2, \pm 3/2$ , and ±1/2 in a $A$ sublattice in presence of an $h'$ external magnetic field, such that $Q$ and $S$ are the nearest-neighbors ferrimagnetically coupled. Using Monte Carlo simulations, we calculate the finite-temperature phase diagrams of magnetization, specific heat, and magnetic susceptibility of the model. The system is defined by a Hamiltonian $(\mathcal {H})$ that contains ferromagnetic next-nearest-neighbors interactions between $S$ spins ($J'_{2}$), as well as external magnetic field and anisotropy interactions at each point of lattice. For a defined range of parameters in $\mathcal {H}$ , the system exhibits discontinuities in their physical variables and spin compensation behaviors. In the planes $J'_{2}-k_{\mathrm{ B}}T'$ and $h'-k_{\mathrm{ B}}T'$ , we analyze the relationship between the critical, compensation, and discontinuous phase transition temperatures with the external magnetic field and the next-nearest-neighbors interaction between $S$ spins. We found that the existence of discontinuous phase transition depends on the strengths of $h'$ and $J'_{2}$. [ABSTRACT FROM AUTHOR]

The minimum point determination method of the magnetic energy surface has been proposed on the basis of magnetic dipole theory in our study. This method can effectively explain the behaviors that the polydisperse magnetorheological fluids (MRFs) can form more complex chain-like structures and the magnetic energy of the particle system will decrease with the formation of the aggregations. The minimum points on the magnetic energy surface of two-particle and three-particle system are observed, and several kinds of stable microstructures are obtained by analyzing these points. Finally, both the stability and evolution mechanism of these microstructures have been explored based on the concept of the magnetic energy barrier. The results demonstrate that a minimum point on the magnetic energy surface of the particle system corresponds to a type of stable microstructure, and the migrations between the minimum points in the systematic magnetic energy phase space can be accounted for the mutual evolutions of these stable microstructures. The microstructural stability depends on the magnetic energy barrier height. For this reason, the microstructural evolution is more likely to appear when the barrier height is relatively low. In the case of sufficient perturbation, the particle system always evolves into the state with lower magnetic energy. [ABSTRACT FROM AUTHOR]

To develop gout diagnosis using magnetic fields and near-infrared light, the orientation behavior of monosodium urate crystals in a highly viscous suspension was characterized. The transmitted light intensity was used to monitor orientation time and behavior within an electromagnet. In glycerol with a viscosity of 1250 $\text {mPa}\cdot \text {s}$ , the crystals were oriented in 4500 s at 100 mT. This was shortened to 360 s when the magnetic field was 500 mT. Similar behavior was observed in a hyaluronic acid solution, which is one component of synovial fluid and which had a viscosity of $960~\text {mPa}\cdot \text {s}$. The crystal orientation times followed theoretical values when the viscosity was $10~\text {mPa}\cdot \text {s}$ or less but were shorter than expected at higher viscosities. In general, the viscosity decreases to about $300~\text {mPa}\cdot \text {s}$ when inflammation occurs in a joint. In this case, the orientation time is expected to be about 1 min. Device applications are possible given the orientation times. [ABSTRACT FROM AUTHOR]

The magnetic susceptibility of pyrolytic graphite (PyG) is temperature dependent. Under an external magnetic field, a levitated PyG sample with a localized temperature change experiences unequal diamagnetic forces. In this paper, we present a study of the macroscale optomechanical displacement of a levitated PyG sample by using a laser source to locally increase the temperature. Dynamic finite-element method simulations show that a localized increase in the sample temperature, simulating a laser source, decreases the diamagnetic force in that local area, leading to the displacement of the PyG sample in the plane of the permanent magnet array. Experimental setups built using different laser sources and samples confirm the range of applicability of the actuation phenomenon to different conditions. An additional setup without moving parts reduced the likelihood by which airflow could have caused the displacement, as we suspect happened in the previous studies. [ABSTRACT FROM AUTHOR]

In this paper, a technique to convert a locally corrected Nyström discretization into a moment method discretization is detailed. The method is general and does not rely directly on any specific relationship between the basis functions used to compute the local corrections and the basis and test functions used in the moment method. The technique is applied to a quasi-magnetostatic volume integral equation for both interpolatory and algebraically constrained moment method bases. Numerical results for a variety of problems in terms of error convergence, system condition number, and degrees-of-freedom are provided. [ABSTRACT FROM AUTHOR]

This paper presents a parameter estimation method to determine the linear behavior of an object constructed of thin plates. Based on the magnetostatic field equations, an integral equation is derived that fully determines the induced magnetization, whenever the spatial magnetic susceptibility distribution is known. This forward problem is used as an underlying physical model for the parameter estimation method. Using near-field magnetic measurements around a thin plate, the parameter estimation yields a distribution of the magnetic susceptibility. Furthermore, a sensitivity analysis is performed to understand the behavior of this parameter estimation method. [ABSTRACT FROM AUTHOR]

Low-temperature magnetic properties were investigated on the gold nano particles (GNPs) with an average size of 11.5 nm, assembled with molecules of ruthenium complex (Ru0), and phenylboronic acid (B0) by the proton nuclear magnetic resonance (1H-NMR) and susceptibility measurements. The temperature dependence of the NMR shift and the uniform susceptibility was described as the sum of the Curie–Weiss term and a positive constant term. From the former, the average number of Ru0 on each GNP was estimated to be 118, which is 23% of the calculation. The finite positive constant term shows a clear contrast with the well-known fact that the bulk gold is diamagnetic. Finally, a disappearance of the motional narrowing effect in the proton NMR spectra below 60 K indicates that the wavering motion of Ru0 complexes on GNP at room temperature is frozen at low temperatures. [ABSTRACT FROM AUTHOR]

We demonstrated crystal structures, magnetic, and optical properties of the B-site substituted double-perovskite Ba2Pr(Bi1−xSbx)O6 (x=0, 0.1, 0.2, 0.25, 0.3, 0.4, 0.5, and 1.0). The single-phase polycrystalline samples with the light Sb substitution are formed in a monoclinic structure (C2}/m). The heavily Sb-substituted samples crystallize in the rhombohedral system accompanied by B-site disorder. Magnetization measurements show that the effective magnetic moments are located around 3.2 μB for the lightly Sb-substituted samples, indicating the valence mixing between Pr3+ and Pr4+. The magnetic moments with the heavy Sb substitution are close to the valence of Pr3+. The magnitudes of bandgap energy for the two end-member samples were estimated from the optical measurements to be Eg = 0.977 eV at x=0 and 2.395 eV at x=1.0. The effect of the bandgap opening due to Sb substitution is examined by using the density functional theory. The lightly and heavily Sb-doped compounds show typical absorption edges in indirect and direct semiconductors, respectively. These findings are qualitatively consistent with the calculated results. [ABSTRACT FROM AUTHOR]

A method is proposed that can efficiently identify the material of a single-organic particle; the identification is realized by improving an apparatus formerly used to observe the field-induced translations of particles. Using this new setup, the material of an unidentified organic particle can be determined without consuming the sample. Specifically, the diamagnetic susceptibility χDIA of the particle was obtained from its translating velocity induced in a field-gradient produced by an Nd magnetic circuit, and its material was identified by comparing the experimental χDIA value with a list of published values. In principle, the proposed method of identification based on the χDIA value is effective even for micrometersized particles because the mass measurement of the sample is unnecessary. Hence, the method can be used to thoroughly extract and identify a rare material from a mixture of heterogeneous particles without consuming the sample, before performing a refined analysis. [ABSTRACT FROM AUTHOR]

The effect of varying the pH on the ac magnetic response of the synthesized iron-oxide nanoparticles (FeOx NPs) embedded in chitosan hydrogel (CH) is experimentally demonstrated. By utilizing the chemical sensitivity of CH in FeOx-CH, we study the effect of changing the rheological property of the CH on the magnetic properties of FeOx NPs. Here, the FeOx-CH is synthesized via in situ precipitation of FeOx during CH gel formation. The morphology of the FeOx-CH is characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The swelling ratio (SR) and the ac susceptibility (ACS) of the FeOx-CH are also investigated as a function of pH. The XRD and TEM results confirm that the synthesized FeOx has a spinel crystal structure with a particle size of 10–20 nm, whereas SEM shows that the hydrogel has a porous structure. The SR result shows that FeOx-CH swells when the pH decreases (acidic). The ACS result shows that the frequency at the peak of the ACS imaginary part (χ″ peak frequency) shifts to higher frequency upon the decrease of pH. From these results, it is inferred that the swelling enhances the Brownian relaxation as suggested by the strong correlation between the SR and χ″ peak frequency at different pH conditions. Analytical calculations are also presented to estimate the change in effective viscosity due to the pH change. [ABSTRACT FROM AUTHOR]

We demonstrated crystal structures, magnetic, and optical properties of the B-site substituted double-perovskite Ba2Pr(Bi1−xSbx)O6 (x=0, 0.1, 0.2, 0.25, 0.3, 0.4, 0.5, and 1.0). The single-phase polycrystalline samples with the light Sb substitution are formed in a monoclinic structure (C2}/m). The heavily Sb-substituted samples crystallize in the rhombohedral system accompanied by B-site disorder. Magnetization measurements show that the effective magnetic moments are located around 3.2 μB for the lightly Sb-substituted samples, indicating the valence mixing between Pr3+ and Pr4+. The magnetic moments with the heavy Sb substitution are close to the valence of Pr3+. The magnitudes of bandgap energy for the two end-member samples were estimated from the optical measurements to be Eg = 0.977 eV at x=0 and 2.395 eV at x=1.0. The effect of the bandgap opening due to Sb substitution is examined by using the density functional theory. The lightly and heavily Sb-doped compounds show typical absorption edges in indirect and direct semiconductors, respectively. These findings are qualitatively consistent with the calculated results. [ABSTRACT FROM AUTHOR]

Magnetic induction field (MIF) of the magnetite particles with five Johnson solid shapes was analyzed using the finite-element method. A new method is proposed to calculate the MIF of irregular magnetite particles by studying their magnetic flux density, and the results show that sphericity is a key factor affecting the MIF of a regular-shaped particle. Moreover, the calculation value of the MIF using particle volume radius ($r$) is more accurate with the higher sphericity. In addition, the relative position is another important factor affecting the accuracy of MIF calculation. The further the distance from the particle center, the more accurate is the MIF. More specifically, when the distance is $4r$ , the average value of the relative difference drops to less than 5.0% with the sphericity of 0.91, 0.92, and 0.93, respectively. Therefore, we suggest that it is feasible to use a sphere MIF instead of an irregular particle MIF to simulate the interaction and motion of massive magnetite particles. [ABSTRACT FROM AUTHOR]

To obtain an accurate hysteresis curve in large Nd–Fe–B sintered magnets at elevated temperatures, we compared the hysteresis curves obtained from the following methods: a superconducting magnet-based vibrating sample magnetometer (SCM-VSM) and the hysteresis graph (HG). Attention was paid to the values of $dJ/dH$ near $H_{\mathrm {cJ}}$ and $H_{k}/H_{\mathrm {cJ}}$ , where $J$ , $H$ , $H_{\mathrm {cJ}}$ , and $H_{k}$ are the magnetization, the magnetic field, coercivity, and knee field, respectively. In the HG method, greater dimensional ratio ($L/D$) led to easier uniform magnetization of cylindrical magnets, causing larger $L/D$ to improve $dJ/dH$ near $H_{\mathrm {cJ}}$ and $H_{k}/H_{\mathrm {cJ}}$. However, the magnetization distortion did not appear at all in the SCM-VSM method at various temperatures and, thus, we could measure the values of $dJ/dH$ near $H_{\mathrm {cJ}}$ and $H_{k}/H_{\mathrm {cJ}}$ as well as the hysteresis curve exactly. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated the critical properties in the vicinity of the ferromagnetic (FM)–paramagnetic (PM) phase transition in a polycrystalline sample of La0.75Ca0.2Ag0.05MnO3, which was prepared by a solid-state reaction method. Temperature dependence of the inverse of the susceptibility $\chi ^{-1}$ ($T$) proves an existence of the Griffiths phase well above Curie temperature ($T_{C} = 230$ K). Detailed analyses of the isothermal magnetization $M$ ($H$ , $T$) data reveal the sample exhibiting a second-order magnetic phase transition, and its temperature dependences of the saturation magnetization and the initial susceptibility obey the asymptotic relations. Using the modified Arrott plots method, the Kouvel–Fisher method, and the critical isotherm analysis, the critical parameters ($\beta$ , $\gamma$ , $\delta$ , and $T_{C}$) of La0.75Ca0.2Ag0.05MnO3 compound have been estimated. Using these critical exponent values, almost $M$ ($H$ , $T$) data measured at different temperatures around FM–PM phase transition are collapsed onto two universal curves of $M/\vert \varepsilon \vert ^{\boldsymbol {\beta }}$ versus $H/\vert \varepsilon \vert ^{\boldsymbol {\beta }+\boldsymbol {\gamma }}$ corresponding to the regular functions for $T > T_{C}$ and $T < T_{C}$ , respectively. [ABSTRACT FROM AUTHOR]

To study how the fat affects the quantification of magnetic susceptibility of iron oxide nanoparticles (IONPs) according to the chemical shift effects, especially at ultra-short echo times, simulation experiments were carried out in this paper. Numerical phantom of IONPs solutions with six different concentrations was designed. Magnetic resonance imaging signals with different fat fractions (ffs) were generated according to a multi-peak chemical shift model. Quantitative susceptibility mapping (QSM) was calculated, and the relationship between the QSM value and ff, as well as echo selection, is evaluated. The results show that streaking artifacts become more and more severe when ff increases, which makes QSM value overestimated. Shortened echo spacing time can reduce streaking artifacts with the same ff. These findings will benefit future clinical evaluations for quantification of iron in vivo. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles have drawn attention recently due to their interesting nanoscopic features and potential applications. Various kinds of ferrite nanoparticles with diameters between 3 and 34 nm encapsulated by amorphous SiO2 were functionalized and examined for biomedical applications. From dc and ac magnetic susceptibility measurements, it was found that these particles followed the Néel relaxation system. Co–Zn ferrite (Co0.8Zn0.2Fe2O4) nanoparticles were prepared and the increase in temperature in the ac field was estimated for hyperthermia treatment. In vitro experiments using cultured human breast cancer cells were carried out, and a dramatic hyperthermia effect was observed. As one of the diagnostic methods, magnetic resonance (MR) measurements were performed for CoFe2O4 nanoparticles, and the samples were also evaluated as potential contrast media for MR imaging. [ABSTRACT FROM AUTHOR]

The phase transformation of FeV ($\sigma$ -phase) to Fe2VAl (L21-phase) has been studied by systematic variation of Al concentration in Fe2V2−xAlx ($x = 0-1$). Remarkable changes in magnetic properties were observed with different Al contents. Electrical transport and magnetic properties of these compositions have been investigated in the temperature range, which revealed that the disorder and impurity phase plays an important role in tuning the electronic properties. The observed magnetic anomalies above $\mathrm{T}_{C}$ indicate the heterogeneous magnetic nature of these alloys. The role of Al in electronic transport and the correlation between structural, magnetic, and electrical transport properties are discussed. [ABSTRACT FROM AUTHOR]

Monosodium urate (MSU) crystals are the cause of gout and are formed from uric acid and sodium. Because they can be rotated by the torque induced by an applied magnetic field, we have characterized their detailed magnetic orientational properties to improve the detection sensitivity from outside the body using the magnetic orientation. The MSU crystals were precipitated by dissolving uric acid powder in aqueous sodium hydroxide. In serum, the MSU crystals were small and uniformly sized, similar to those obtained from gout patients. The MSU crystals were not completely oriented perpendicular to the magnetic-field direction, but rather the c-axis of the crystal was inclined with respect to the field direction. Specifically, they were inclined at a mean of 69.3° under a magnetic field of 500 mT. The MSU crystals were not perfectly oriented in magnetic fields <200 mT. The inclination results from the molecular structure of the MSU crystal. [ABSTRACT FROM AUTHOR]

Chalcogenide bulk spinels with general formula CuCr2X4 (X = S, Se, and Te) are ferromagnetic and p-type metallic materials with the thermoelectric figure of merit of 0.15. They can be used to dope or alloy with related semiconducting spinels. Therefore, it is expected that their nanosized crystallites display also unique properties and new potential applications. This paper presents the results of dc and ac magnetic measurements, including the higher harmonics of ac magnetic susceptibility as well as electrical conductivity and thermoelectric power of the CuCr2S4 nanospinels. These studies showed that decreasing the size of crystallites to nanometer scale leads to a dramatic change in their physical properties. [ABSTRACT FROM AUTHOR]

AC magnetic susceptibility and optical transmission measurements were performed on Ni nanorod suspensions for ac and superimposed dc magnetic fields up to 9 mT. With the comparably large magnetic moment per nanorod, these field values correspond to Langevin parameters $\xi$ up to about 80. These wide range of \xi$ values, the narrow size distribution, and the absence of Néel relaxation make these single-domain ferromagnetic nanorods ideally suited for the experimental verification of the dependence of the Brownian relaxation time on ac and dc magnetic fields. Consistent results for the magnetic moment m and the zero-field Brownian relaxation time \tau _{B,0} were obtained for all measurement modalities and the valid field range of alternative models for the ac susceptibility was evaluated. [ABSTRACT FROM AUTHOR]

The magnetic core-size distribution of magnetic nanoparticles (MNPs) was estimated from three independent measurements, i.e., magnetization, ac susceptibility (ACS), and magnetic relaxation (MRX). First, distribution of magnetic moment m in MNP sample was estimated by analyzing the static magnetization ( M – H) curve of the MNP sample in suspension. Next, distribution of anisotropy energy E was estimated by analyzing the ACS of immobilized MNP sample measured from 10 Hz to 1 MHz. The ACS measurement in much lower frequency range was substituted by the MRX measurement. MRX of immobilized MNP sample was measured from 2 to 10^4 s, corresponding to the frequency range from 10^-4 to 0.5 Hz in ACS measurement. The relaxation curve was analyzed using a newly developed analytical method to estimate the E distribution of the MNPs in the range of large E values. Then, the estimated distributions of m and E were transferred to the distributions of magnetic core size. Core-size distributions obtained from m and E distributions reasonably agreed with each other. Namely, we obtained similar core-size distribution from static and dynamic properties of MNP sample, confirming the validity of the present method. Therefore, the present method can be useful to estimate the core-size distribution of MNP sample. [ABSTRACT FROM AUTHOR]

Measurements of the ac susceptibility (ACS) as a function of frequency have been widely applied for the determination of structure parameters of magnetic nanoparticles (MNP). The analysis of spectra of real and imaginary parts measured on suspensions of MNP is generally based on the Debye model, extended by distributions of size parameters. Here, we compare different modifications of the Debye model with experimental data recorded on suspensions of single-core and multi-core iron-oxide nanoparticles. The applied models also depend on whether the nanoparticle’s magnetic moments are thermally blocked and whether both Brownian and Néel relaxation have to be taken into account. The obtained core and hydrodynamic size parameters are compared with those from transmission electron microscopy and dynamic light scattering. Whereas structure parameters can be reliably determined for single-core nanoparticles, the interpretation of ACS spectra measured on multi-core nanoparticles is more complicated, especially regarding the contribution of particles relaxing via the Néel mechanism. Depending on the packing density and thus the interaction between cores in a particle, the effective core parameters derived from the spectrum must be interpreted with care. [ABSTRACT FROM AUTHOR]

We have experimentally verified the ac susceptibility model by Shliomis and Stepanov which accounts for the anisotropy caused by the different directions of the easy axes of the magnetic nanoparticle (MNP) cores with respect to the applied ac magnetic field. To experimentally access the anisotropy, single-core MNPs were immobilized in the absence of a magnetic field, thus causing random orientations of easy axes, and in a static magnetic field of 170 mT, thus orienting the nanoparticles’ easy axes either parallel or perpendicular to the ac field. In agreement with theory, the real part of the sample with easy axes aligned perpendicularly to the ac field is constant while the imaginary part is zero. In contrast, the real part of the sample with parallel-oriented easy axes decays with increasing frequency. The susceptibility spectra of the sample with random orientation of easy axes are in between the other two cases according to \chi (\omega ) = (\chi \textrm {II}(\omega ) + 2\chi \bot (\omega )) /3. This anisotropic behavior also explains why the real part of suspensions of thermally blocked MNPs does not drop down to zero at high frequencies but to a finite value. This value allows one to independently estimate the effective anisotropy constant of MNPs. [ABSTRACT FROM AUTHOR]

The magnetic behavior of a material is determined by its microstructure, or more precisely, by the configuration of electrons and their interactions with lattices. It has been difficult to control the microstructures of polycrystalline metallic nanowires through electrochemical deposition. Here, we report the synthesis, microstructure, and magnetic properties of nickel (Ni) nanowires from the viewpoints of crystallographic orientation and grain size. Changes in both the Ni precursor and buffer solution result in a remarkable modification of crystallographic orientation and magnetocrystalline anisotropy energy, and consequently, a difference in magnetic susceptibility is observed. In addition, a significant enlargement in grain size with a [220] texture is observed when raising the temperature during electrochemical deposition and subsequently brings a decrease in experimental coercivities. [ABSTRACT FROM AUTHOR]

The NiCuZn ferrites doped with Bi2O3 and Co2O3 were prepared by the solid-state reaction method. Micrographs were obtained by SEM. The complex permeability spectra were measured by Agilent E4991A and 16454A. Variation of the permeability under a magnetic field impulse was measured by Agilent 4284A. Effect of the Co2O3 content on the permeability spectra of the NiCuZn ferrite samples before and after exposing to an impulse magnetic field was discussed. The corresponding permeability spectra of the samples were decomposed into the domain wall motion component and the spin rotation component. The results show that the permeability at 1 MHz decreases and the resonance frequency increases with more Co2O3 content, and Co2+ have different effect on the two kinds of magnetic susceptibility components. Different variation was revealed for the domain wall motion component and the spin rotation component after exposing to an impulse magnetic field. The decline rate of susceptibility by domain wall motion is smaller than that of susceptibility by spin rotation. [ABSTRACT FROM PUBLISHER]

The equivalent magnetic noise spectral density of giant magnetoimpedance (GMI)-based sensors exhibits a low-frequency excess noise inversely proportional to the frequency (1/f noise). In order to enhance the performance and reach the ultimate and intrinsic limit of the magnetometer, it is necessary to investigate the origin of this excess noise. Cross correlation measurements have permitted the demonstration that the excess low-frequency noise arises from the sensor, under defined excitation conditions, particularly the amplitude of the excitation current and the dc bias current. Given that the GMI effect is based on an impedance variation governed by the magnetization direction under an applied external magnetic field, the low-frequency magnetization fluctuations within the GMI wire have been considered to be a possible noise source. The fluctuation-dissipation theorem permits evaluation of the spectral power density of these fluctuations, which is proportional to the imaginary part of the susceptibility, \chi ^\prime \prime . The latter may be evaluated by two different methods, based on the measurement of the real part of the wire impedance and on the evaluation of the circumferential hysteresis loop area. The results obtained by both methods are compared and discussed. The values of \chi ^\prime \prime thus obtained are then used in order to predict the equivalent magnetic noise level at 1 Hz, and are compared with that measured at 1 Hz. The comparison is conducted for different amplitudes of the dc bias current, and the results obtained indicate that the proposed methods have the potential of predicting the excess noise in GMI sensors. [ABSTRACT FROM PUBLISHER]

This paper presents an equivalent strain approach to reduce multiaxial magneto-elastic configurations into 1-D descriptions. It follows similar principles as those used for equivalent stress approaches. The approach can be easily implemented into magneto-elastic constitutive equations using strain as driving mechanical state variable. It is particularly useful to describe 3-D configurations when only 1-D measurements are available to describe the magneto-elastic behavior. [ABSTRACT FROM AUTHOR]

Contemporary ships, made of ferromagnetic materials, under the influence of earth’s magnetic field produce an underwater magnetic anomaly. This anomaly, often called the magnetic signature, compromises the stealth and safety of the ship and needs to be minimized. This paper presents an efficient methodology for the design of optimal tri-axial degaussing system and estimation of coil currents in ships to minimize the magnetic signature of the ship. Designing such a system is a complex optimization problem, and we address this problem with high-dimensional variable selection technique along with linear regression techniques. [ABSTRACT FROM AUTHOR]

To obtain a more accurate hysteresis curve for large Nd-Fe–B sintered magnets with high coercivity ( $H_{{\mathrm {cJ}}}$ ), we employed a superconducting magnet-based vibrating sample magnetometer (SCM-VSM), which is independent of the drift. The demagnetization curves around $H_{{\mathrm {cJ}}} resulting from the SCM-VSM, the hysteresis graph (HG), and the pulsed-field (PF) magnetometer were compared. Attention was paid to the accurate correction of the demagnetizing field ( Hd ) for the cylindrical samples using a magnetometric demagnetizing factor dependent on the aspect ratio ( L/D ) and differential coefficient of the measured curve ( $dJ/dH_{{\mathrm {ex}}}$ ), where $L$ , $D$ , $J$ , and $H_{{\mathrm {ex}}}$ are the length and diameter of sample, magnetization, and applied field, respectively. The cylindrical samples used were kept at a $D$ of 10 mm and an $L$ of 7 and 14 mm. The hysteresis curves and magnetic properties obtained from the SCM-VSM method agreed very well with one another, except for the differential susceptibility ( $dJ/dH_{{\mathrm {eff}}}$ ) near $H_{{\mathrm {cJ}}}$ using different shapes (cylinders and sphere) and sizes of magnets, where $H_{{\mathrm {eff}}} is the effective field. The squareness ratio ( Hk / H{\mathrm {cJ}} ) and $dJ/dH_{{\mathrm {eff}}}$ near $H_{{\mathrm {cJ}}} obtained from the SCM-VSM method were found to be superior to those obtained from the PF method, where Hk is the knee field. For the sample with a higher H{\mathrm {cJ}} ( $\geq 2$ MA/m), the abnormality of $J$ on the demagnetization curve had direct effects upon $dJ/dH_{{\mathrm {eff}}}$ near $H_{{\mathrm {cJ}}} and Hk / H{\mathrm {cJ}} in the HG method. However, a larger $L/D$ has an effect on improving these values as has been previously found in this paper. For large magnets, the values of $dJ/dH_{{\mathrm {eff}}}$ near $H_{{\mathrm {cJ}}} and Hk / H{\mathrm {cJ}} were influenced by the correction of the eddy current in the PF method. [ABSTRACT FROM AUTHOR]

We introduce magnetic field sensor bridges that are formed by combinations of stripes of an exchange-pinned magnetic stack displaying anisotropic magnetoresistance. We present a systematic overview on how the stripe geometries can be combined to form sensor bridges with a scalable signal and how these can be tailored toward detection of external magnetic fields and of magnetic beads over or tethered to the sensor surface. Particular attention is given to the case where the beads are magnetized by the sensor self-field due to the bias current passed through the sensor, which is interesting for magnetic bead sensing and where the static and dynamic magnetic bead response can be monitored in the second harmonic sensor response to an oscillating bias current. The recent literature on applications of these sensors for the detection of magnetic fields and of the dynamic and static response of magnetic beads in suspension and attached to the sensor surface is reviewed as well as the use of the sensors for magnetic biosensing in volume- and surface-based formats. We illustrate that the sensors can be flexibly designed and applied for a number of sensing applications with sensitive detection of magnetic fields down to the nanotesla range. [ABSTRACT FROM PUBLISHER]

This paper presents the results of a broadband microwave spectroscopy of a diluted water-based ferrofluid, when subject to an external polarizing magnetic field (PMF) of variable intensity. The characterization has been performed exploiting a recently proposed measurement approach, specifically devised to enable accurate measurement of the magnetic properties of such suspensions, properly modified to consider the presence of an applied PMF. To investigate in detail the nature of the response and of its dependence on the applied PMF, the measured susceptibilities have been fitted with a superposition of relaxation and resonance dispersion models. Besides quantitatively assessing results already reported in the literature for similar magnetic nanoparticles (MNPs), but suspended in hydrocarbons the analysis has also led to an unexpected result, namely, the onset of a second ferromagnetic resonance when the PMF exceeds 20 kA/m. Apart from their physical interest, the obtained results provide an accurate and comprehensive characterization of the magnetic response of a class of MNPs exploitable in all the emerging biomedical applications based on the interaction of MNPs and electromagnetic fields, such as microwave imaging. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles (MNPs) have emerging applications as tracer agents in medical diagnosis and for image guidance in surgery and targeted drug delivery. A critical component of the translation of MNPs into clinical use is an accurate understanding of the induced magnetic response to applied time-varying (ac) and static (dc) magnetic fields. Here, we propose a way of obtaining a Volterra series inspired model to predict the nonlinear behavior of MNPs in a single characterization step. For this purpose, we built an apparatus measuring the nonlinear responses of MNPs to frequencies from 1 to 5 kHz, applied ac magnetic fields from 1 to 5 mT, and applied dc magnetic fields from −5 to 5 mT. Using these characterization data, we then fit a reduced Volterra series inspired model to the nonlinear dynamic responses of the first seven harmonic frequencies of the ac excitation ( R^2 > 0.99 ). This model could offer a practical alternative to physical modeling for MNP imaging methods, such as nonlinear susceptibility magnitude imaging (nSMI). Volterra series modeling as demonstrated in this paper could overcome the need for empirical calibration of the MNP response to external magnetic fields before imaging. This approach would eliminate one of the critical barriers to the translation of nSMI into clinical use. [ABSTRACT FROM AUTHOR]

For the spherical kagome system {W72V30}, which is a magnetic cluster with 30 V4+ ions, recent experimental and theoretical studies on the magnetization process at low temperatures have indicated that Dzyaloshinskii–Moriya interaction is an important ingredient in this material. In this paper, we use microcanonical thermal pure quantum (mTPQ) states to calculate the temperature dependence of the magnetic susceptibility and compare our calculated results with an existing experimental susceptibility. These mTPQ states are generated to reproduce the smooth microcanonical ensemble, which is difficult from the canonical ensemble. We show that adequate choice of a parameter in the generation procedure of mTPQ states leads to the same temperature dependence as the canonical ensemble. [ABSTRACT FROM AUTHOR]

Recently developed superparamagnetic scaffolds for bone tissue engineering are still a complex object to deal with. Thanks to the possibility of controlling them remotely and directing therapeutic action in a non-invasive way, this work deals with the necessity of a clear definition and quantification of the field gradient, the forces and velocity it could exert on magnetic nanocarriers in a static magnetic field, and the heat and power generated when a time-varying field is applied, better defining the frequency response of magnetic nanoparticles entrapped in a solid matrix. [ABSTRACT FROM PUBLISHER]

LuMn2O5 multiferroic nanorods were fabricated using the hydrothermal method with three sizes of diameters ( \langle LC\rangle )\times \text {axial} lengths of 66(22) \text nm\times 18 (5) nm, 78(38) \text nm\times 22 (9) nm, and 91(35) \text nm\times 20 (7) nm, as determined by the field emission transmission electron microscope and selection area electron diffraction. A small ferrimagnetic (FIM) peak was obtained at 27 K from the nanorods with \langle LC\rangle = 66 and 78 nm, and the 91 nm sample exhibited FIM behavior below 43 K. All the samples had a hysteresis loop at 2 K. The fitted \mu \mathrm{ eff} (effect moment), T\mathrm {so} (spin-orbit interaction), and the coercively greatly increased with size to \langle LC\rangle = 91 nm. These results reveal that the size importantly affects the magnetic properties between \langle LC\rangle = 78 and 91 nm. Raman spectra were obtained at various temperatures to determine the effects of the size on the \langle LC\rangle = 78 and 91 nm samples. The red-shift of the \textA\mathrm {g}+\mathrm {B}\mathrm {1g} mode increased with temperature only for the 91 nm sample, revealing that the interaction between the Mn–O bonds is more sensitive to temperature in larger LuMn2O5 nanorods. [ABSTRACT FROM PUBLISHER]

Low-frequency (LF), low-amplitude alternating current (ac) magnetic fields are approved by the U.S. Food and Drug Administration as an adjunct to the orthopedic surgery procedure (spinal fusion surgery) and for the treatment of selected bone healing complications (fracture non-union). The biological effects are understood to rely on a contact-less induction of electric currents in the electrically conducting compartments of the bone. Here, we investigate another potential mechanism of the LF magnetic field effect on bone by measuring mechanical force on bone due to its diamagnetic susceptibility. The biological rationale is the bone’s exquisite sensitivity to local mechanical stresses that determine its structure and physiology. Thus, the periodic magnetic microstress effects on bone over an extended period of the typical clinical LF magnetic field application (hours daily over a period of a few months) could contribute to bone regeneration. The aim was to demonstrate the diamagnetic field effect on thin, human cortical bone slice preparations (from commercial tissue repository) suspended in the vicinity of a rotating cylindrical, diametrically magnetized permanent magnet. The data provide a basis for the calculation of diamagnetic microstresses generated by the clinical LF magnetic field stimulation devices and their significance as potential contributing factors to the biological mechanism of action of LF ac magnetic fields. [ABSTRACT FROM PUBLISHER]

Online magnetic nondestructive evaluation (NDE) of dual-phase (DP) steels is made on bands submitted to high multiaxial stress. Extraction of microstructural information from the measurement requires separating the effect of stress and microstructure. Coupled magnetomechanical micromagnetic modeling is relevant for that purpose. In this paper, the magnetic behavior of a DP steel under biaxial stress is carried out and compared with the modeling. It is shown that the discrepancies observed between experiments and model can be explained by the 2-D assumption. [ABSTRACT FROM AUTHOR]