Spin-rotation Mechanism Research Articles

Fe4N soft magnetic composite with ultra-low eddy current loss and excess loss above megahertz

In this study, Fe4N particles were synthesized from pure iron by gas nitridation and then fabricated into soft magnetic composite through silica-polyurethane insulation combined with warm compaction. The composite exhibits excellent soft magnetic properties in the several-megahertz frequency range. The complex permeability spectra of Fe4N composite show a remarkable frequency stability, with the real part remaining nearly constant below 100 MHz. The resonance frequencies of domain wall motion mechanism and spin rotation mechanism are up to 481 MHz and 2.24 GHz, respectively, which are ten times higher than those of Fe composite. Due to the effective suppression of both eddy current loss and excess loss, the total core loss decreases to 725.6 kw/m3 at 3000 kHz and 10 mT, exhibiting almost a linear growth with frequency. These outstanding properties are mainly due to the relatively large magnetocrystalline anisotropy and high resistivity of Fe4N particles. In addition, Fe4N composite also exhibits an excellent DC bias performance, maintaining over 98 % permeability under a superimposed magnetic field of 100 Oe. This study presents an effective solution for suppressing eddy current and excess losses at high frequencies, offering potential for the application of power inductors in high-frequency scenarios.

Performance optimization of FeSiCr/ZnO soft magnetic composites by highly orientation and domain wall engineering

The power loss and permeability of soft magnetic composite (SMC) might be improved by surface modification and magnetic field orientation of flake particles. The oriented ZnO-modified flaky FeSiCr SMCs were produced under the magnetic field. The orienting mechanism of flake powder under a magnetic field produced by Helmholtz coils was investigated using torque model analysis. After surface modification, the permeability and power loss of ZnO-modified flaky FeSiCr SMCs could reach 63 and 421.29 kW/m3(at 50 mT, 100 kHz), respectively. The three-dimensional loss separation results demonstrate that spin rotation mechanism, defects, and dislocations of ZnO modification from theory and experiment may be responsible for the enhanced soft magnetic characteristics.

A spin–rotation mechanism of Einstein–de Haas effect based on a ferromagnetic disk

A spin–rotation mechanism of Einstein–de Haas effect based on a ferromagnetic disk

Squeezing formaldehyde into C60 fullerene

The cavity inside fullerene C60 provides a highly symmetric and inert environment for housing atoms and small molecules. Here we report the encapsulation of formaldehyde inside C60 by molecular surgery, yielding the supermolecular complex CH2O@C60, despite the 4.4 Å van der Waals length of CH2O exceeding the 3.7 Å internal diameter of C60. The presence of CH2O significantly reduces the cage HOMO-LUMO gap. Nuclear spin-spin couplings are observed between the fullerene host and the formaldehyde guest. The rapid spin-lattice relaxation of the formaldehyde 13C nuclei is attributed to a dominant spin-rotation mechanism. Despite being squeezed so tightly, the encapsulated formaldehyde molecules rotate freely about their long axes even at cryogenic temperatures, allowing observation of the ortho-to-para spin isomer conversion by infrared spectroscopy. The particle in a box nature of the system is demonstrated by the observation of two quantised translational modes in the cryogenic THz spectra.

Ultrahigh Permeability at High Frequencies via A Magnetic-Heterogeneous Nanocrystallization Mechanism in An Iron-Based Amorphous Alloy.

The prevalence of wide-bandgap (WBG) semiconductors allows modern electronic devices to operate at much higher frequencies. However, development of soft magnetic materials with high-frequency properties matching the WBG-based devices remains challenging. Here we report a promising nanocrystalline-amorphous composite alloy with a normal composition Fe75.5 Co0.5 Mo0.5 Cu1 Nb1.5 Si13 B8 in atomic percent, producible under industrial conditions, which shows an exceptionally high permeability at high frequencies up to 36000 at 100kHz, an increase of 44% compared with commercial FeSiBCuNb nanocrystalline alloy (25000±2000 at 100kHz), outperforming all existing nanocrystalline alloy systems and commercial soft magnetic materials. The alloy is obtained by a unique magnetic-heterogeneous nanocrystallization mechanism in an iron-based amorphous alloy, which is different from traditional strategy of nanocrystallization by doping non-magnetic elements (e.g., Cu and Nb). The induced magnetic inhomogeneity by adding Co atoms promotes locally the formation of highly ordered structures acting as the nuclei of nanocrystals, and Mo atoms agglomerate around the interfaces of nanocrystals, inhibiting nanocrystal growth, resulting in an ultrafine nanocrystalline-amorphous dual-phase structure in the alloy. The exceptional soft magnetic properties are shown to be closely related to the low magnetic anisotropy and the unique spin rotation mechanism under alternating magnetic fields. This article is protected by copyright. All rights reserved.

Т1 mappingofratlungsin19 FMRIusing octafluorocyclobutane.

To demonstrate the feasibility of using octafluorocyclobutane (OFCB, c-C4 F8 ) for T1 mapping of lungs in 19 F MRI. The study was performed at 7 T in three healthy rats and three rats with pulmonary hypertension. To increase the sensitivity of 19 F MRI, a bent-shaped RF coil with periodic metal strips structure was used. The double flip angle method was used to calculate normalized transmitting RF field (B1n + ) maps and for correcting T1 maps built with the variable flip angle (VFA) method. The ultrashort TE pulse sequence was applied for acquiring MR images throughout the study. The dependencies of OFCB relaxation times on its partial pressure in mixtures with oxygen, air, helium, and argon were obtained. T1 of OFCB linearly depended on its partial pressure with the slope of about 0.35 ms/kPa in the case of free diffusion. RF field inhomogeneity leads to distortion of T1 maps built with the VFA method, and therefore to high standard deviation of T1 in these maps. To improve the accuracy of the T1 maps, the B1n + maps were applied for VFA correction. This contributed to a 2-3-fold decrease in the SD of T1 values in the corresponding maps compared with T1 maps calculated without the correction. Three-dimensional T1 maps were obtained, and the mean T1 in healthy rat lungs was 35 ± 10 ms, and in rat lungs with pulmonary hypertension-41 ± 9 ms. OFCB has a spin-rotational relaxation mechanism and can be used for 19 F T1 mapping of lungs. The calculated OFCB maps captured ventilation defects induced by edema.

Magnetic and magnetostrictive properties of the ternary Fe67.5Pd30.5Ga2 ferromagnetic shape memory ribbons

Specific functional characteristics of the ferromagnetic shape memory alloy Fe67.5Pd30.5Ga2 prepared as ribbons by rapid quenching technique are reported. The shift of the martensitic transformation temperature induced by the applied magnetic field was determined from the thermomagnetic measurements at various fields up to 5T being proved to be in good agreement with the result obtained from calorimetric data via the Clapeyron - Claussius relation. Magnetostriction measurements reveal a pure spin rotation mechanism under low applied magnetic fields, allowed by the reduced magnetic anisotropy. In high magnetic fields and at temperatures close to martensitic transformation, the magnetostriction has a linear increase up to the maximum considered magnetic induction of 3T. This behavior has been discussed in connection with the forced magnetostiction aspects.

Molecular Interactions and Mechanisms in the 1H NMR Relaxation of Residual CHCl3 in Deuterochloroform Solution of a Two-Chain Ionic Surfactant

1H NMR spin–lattice (T1) and spin–spin (T2) relaxation times have been measured for the residual CHCl3 component of deuterochloroform (99.8 atom% D) in neat solvent samples and in a series of isotropic solutions of the ionic surfactant n-octylammonium-n-octadecanoate and also in degassed/dried and aerated solvent systems at 298 K. Analysis of the proton relaxation times as composite values from various relaxation mechanisms suggests that the spin–lattice process is predominantly via spin–rotation while spin–spin relaxation principally involves 1H–Cl scalar coupling. Rotational correlation times from relaxation rates via the dipolar and spin–rotation mechanisms reveal similar fast picosecond molecular rotation of chloroform in the different samples. The presence of surfactant in the solution appreciably affects the 1H NMR spin–lattice relaxation time of CHCl3 and the chemical shift, which is concentration dependent owing to weak intermolecular interactions. Effects of sample condition and solvent degassing, drying, and aeration treatments on the NMR relaxation times and line shape properties of the residual CHCl3 isotopomers are also examined.

Processing–microstructure–properties relationship in a CuNiZn ferrite

CuNiZn ferrites are polycrystalline ceramic materials that are used widely in electronic devices for a number of reasons, including their high permeability in the RF frequency region, electrical resistivity, mechanical hardness and chemical stability. One of their main applications is in the production of specimens to prevent possible interferences between electronic devices, thanks to their ability to absorb electromagnetic waves. However, their electromagnetic properties are not solely dependent on their chemical composition, but also on the microstructure of the final piece (relative density or total porosity, grain size distribution, pore size distribution, the nature of the grain boundary, presence of secondary phases, dopants, etc.) and, therefore, on the morphology and size of the starting particles, and the processing method.The microstructure of the sintered specimens was designed in such a way as to optimize the electromagnetic properties of this ferrite. The solid-state sintering stage was also modeled with this optimization in mind. This sintering model enabled to propose the material transport mechanisms that controlled the densification and grain-growth rates, as well as the relative rates of these two simultaneous processes. The established relationships facilitate the design of a thermal cycle suitable for the manufacture of ferrite pieces with maximum relative density and the necessary microstructure. Together with the pre-configured chemical composition, the idea is that this ensures a strong set of final electromagnetic properties.The electromagnetic properties of the sintered ferrites were observed to improve as sintered relative density and average grain size increased, provided there was no evidence of exaggerated grain growth. In this sense, it seems there is a threshold of the grain size as of which the electromagnetic properties of the sintered specimens get worse. A linear relationship was observed between the imaginary part of the complex magnetic permeability and average grain size, provided each of the different magnetization mechanisms contributing to the complex permeability of the ferrite are taken into account (i.e. spin rotation and wall motion mechanisms).

Cold collisions of heavy Σ2 molecules with alkali-metal atoms in a magnetic field: Ab initio analysis and prospects for sympathetic cooling of SrOH(Σ+2) by Li(S2)

We use accurate ab initio and quantum scattering calculations to explore the prospects for sympathetic cooling of the heavy molecular radical SrOH($^2\Sigma$) by ultracold Li atoms in a magnetic trap. A two-dimensional potential energy surface (PES) for the triplet electronic state of Li-SrOH is calculated ab initio using the partially spin-restricted coupled cluster method with single, double and perturbative triple excitations and a large correlation-consistent basis set. The highly anisotropic PES has a deep global minimum in the skewed Li-HOSr geometry with $D_e=4932$ cm$^{-1}$ and saddle points in collinear configurations. Our quantum scattering calculations predict low spin relaxation rates in fully spin-polarized Li+SrOH collisions with the ratios of elastic to inelastic collision rates well in excess of 100 over a wide range of magnetic fields (1-1000 G) and collision energies (10$^{-5}-0.1$~K) suggesting favorable prospects for sympathetic cooling of SrOH molecules with spin-polarized Li atoms in a magnetic trap. We find that spin relaxation in Li+SrOH collisions occurs via a direct mechanism mediated by the magnetic dipole-dipole interaction between the electron spins of Li and SrOH, and that the indirect (spin-rotation) mechanism is strongly suppressed. The upper limit to the Li+SrOH reaction rate coefficient calculated for the singlet PES using adiabatic capture theory is found to decrease from $4\times 10^{-10}$~cm$^3$/s to a limiting value of $3.5\times 10^{-10}$ cm$^3$/s with decreasing temperature from 0.1 K to 1 $\mu$K.

Manipulating the Magnetization of a Nanomagnet with Surface Acoustic Waves: Spin-Rotation Mechanism

A century ago, Samuel Barnett magnetized a large body by mechanical rotation, and Albert Einstein and Wander de Haas observed rotation of a solid produced by a change in its magnetization. These effects are weak when the rotation is slow, but local mechanical rotations produced by high-frequency surface acoustic waves (SAWs) are very fast. The authors show that one can reverse the moment of a nanomagnet on a solid's surface via SAWs generated by short voltage pulses, for logic and memory applications.

Back interface effect on the topography and magnetism relationship studied from Ni nano-coatings: role of ITO and Cu substrates

A comparative study is here reported on the role of ITO and Cu substrates in the surface growth, topography and the magnetism of mesoscopic scale thick nanocrystallized Ni electrocoatings in the thickness interval 60 < d < 1200 nm. The cathodic voltammetry (C-V) technique used for the coating formation engenders conglomerated grain patterns with ITO and spaced needle-like features with Cu. These surface configurations are particularly marked with the thinnest samples. They undergo a noticeable smoothing with the coating thickness increase. The magnetic reversal (MR) of the Ni samples on Cu is ruled by the spin rotation mechanism. A transition from the domain wall (DW) motion mechanism to the spin rotation one occurs with ITO while the d value increases. The study of the topography-magnetism relationship reveals that the spin rotation mechanism of the Ni samples is incoherent with both substrates. The co-existence of the Bloch magnetic domains (MD)B and the Néel domain wall (DW)N types is identified for ITO in the thinner (rougher) Ni samples associated with the DW motion MR. The same sequence occurs for Cu for the thicker (smoother) samples linked to the spin rotation MR, as long as their normalized roughness values are confined below σo′ ≈ 0.15.

Complex permeability spectra of PbO and Ta2O5 added nanocrystalline MgCuZn ferrites

PbO and Ta2O5 added MgCuZn ferrites are prepared by the Microwave–Hydrothermal (M–H) processing. The nanocrystalline ferrites are sintered to a temperature of 900°C/4h. SEM pictures reveal that, the addition of PbO causes a small amount of grain growth, whereas the addition of Ta2O5 causes a fine-grained microstructure. The complex permeability spectra (µ⁎=μ′−iμ″) of the prepared samples were measured in the frequency range from 1MHz to 1.8GHz, the µ⁎ spectra are analyzed into two magnetization processes with focus on the particle size of ferrite samples. In addition to the spin rotation relaxation in 130–200MHz, it is initially identified the contribution from reversible domain wall bowing rising at 6–40MHz. The magnetic state of the ferrite is also influenced by the addition of PbO and Ta2O5. The spin rotation mechanism of the present ferrites is enhanced by the preparation of nanocrystalline samples.

Nanoscale Topography and Magnetic Structure of Nanocrystallized Nickel Electrodeposits

The microstructure and magnetic properties of nickel films thick of 100 till 1000 nm are here investigated. They are deposited on polycrystalline Cu substrate by cathodic voltammetry (CV) technique varying the scan rate in the interval 0.17 ≤ r ≤ 1.67 mV/s. Thicker and rougher samples grow at lower r values while thinner and smoother ones are obtained at the higher r values. All the samples obtained exhibit a negative strain indicating a compressive stress that decreases with the film thickness increase. The magnetic reversal of the Ni films is ruled by the spin rotation mechanism associated with their low squarness of about 28%. The study of their ferromagnetic-topography dependence reveals that their magnetic domains always remain of the Néel type (MD)N in the investigated r values according to the model of Zhao et al. [J. Appl. Phys. 89, 1325(2001)]. The magnetic anisotropy of the Ni samples exhibit a out-of-plane component that becomes sensitively marked with the increase of the film thickness.

Ortho-para transition of interstitialH2andD2in Si

The ortho-para transition of interstitial ${\text{H}}_{2}$ in Si has been observed in a recent Raman study [M. Hiller et al., Phys. Rev. Lett. 98, 055504 (2007); M. Hiller et al., Phys. Rev. Lett. 99, 209901 (2007)]. In order to address issues that are difficult to study by Raman spectroscopy, we have performed IR-absorption experiments to further investigate this ortho-para transition. We find that when a Si sample containing ${\text{H}}_{2}$ that has been equilibrated at room temperature is subsequently held at 77 K, the $3618.4\text{ }{\text{cm}}^{\ensuremath{-}1}$ IR line assigned to ortho-${\text{H}}_{2}$ is reduced in intensity with a single exponential time constant of 229 h as the system relaxes to the para-${\text{H}}_{2}$ state. The previous Raman data had been analyzed by a model in which the ortho-para transition is caused by an interaction with the nuclear magnetic moment of $^{29}\text{S}\text{i}$ (4.7% abundant) that is present in natural Si. However, in order for every ${\text{H}}_{2}$ molecule to interact with a $^{29}\text{S}\text{i}$, at least six shells of Si neighbors must be considered. Because of the strong dependence of the transition rate on the $^{29}\text{S}{\text{i-H}}_{2}$ distance, the kinetics of such a transition should be highly nonexponential. Thus, our IR data are not consistent with this mechanism. We have also investigated the para-ortho transition of interstitial ${\text{D}}_{2}$ and have found decay rates similar to those for the ortho-para transition of ${\text{H}}_{2}$. We have considered two possible mechanisms for this transition: ${\text{H}}_{2}$ or ${\text{D}}_{2}$ tunneling, which would allow the molecule to sample tetrahedral sites adjacent to $^{29}\text{S}\text{i}$, and spin-rotation coupling that can act while the molecule is dynamically off-center. Consideration of a possible tunneling rate by theory and the similarity of the ${\text{H}}_{2}$ and ${\text{D}}_{2}$ results seem to rule out the tunneling mechanism but not the spin-rotation mechanism. These results clearly show that the mechanism of the ortho-para transition for ${\text{H}}_{2}$ and ${\text{D}}_{2}$ in Si remains an experimental and a theoretical challenge.

Probing Systems in Solution by NMR Using Sulfur Hexafluoride as a Spy Molecule

The use of SF6 as a spy molecule in solution-state NMR is investigated as an alternative to 129Xe NMR. 19F chemical shift, longitudinal relaxation time, and integral measurements, as well as intermolecular nuclear Overhauser effects, are reported for SF6 dissolved in simple deuterated solvents and/or in various solutions among which are aqueous solutions of cucurbit[6]uril (CB) and alpha-cyclodextrin (alphaCD). Both CB and alphaCD form a 1:1 inclusion complex with SF6. In a 0.2 M D2SO4-D2O solution, the affinity of CB for SF6 is 2.9x10(5) L mol(-1) at 298 K; it is the largest value ever found for the inclusion of a neutral guest into the CB cavity. It is one order of magnitude larger than in a 0.2 M Na2SO4-D2O solution, and the role of the cation is evidenced. In D2O, the affinity of alphaCD for SF6 is about 25 L mol(-1). With CB, the kinetics is slow on both the 1H and 19F chemical shift time scales, while with alphaCD fast exchange is observed. The 19F chemical shift of SF6 is much less sensitive to medium effects than the chemical shift of 129Xe. This might be a limitation if minute structural changes are to be investigated but, in the present study, turned out to be an advantage for determining the affinity of alphaCD for SF6. With CB, the 19F chemical shift of included SF6 is found to be sensitive to the nature of the cation bound at the portals. The 19F relaxation time of SF6 dissolved in deuterated solvents is dominated by the spin-rotation mechanism and is orders of magnitude shorter that the 129Xe relaxation time. It is found to be rather sensitive to the environment and was used to determine the affinity of alphaCD for SF6. The detection limit of SF6 by 19F NMR is lower than the NMR detection limit of thermally polarized 129Xe by more than three orders of magnitude. It lies in the micromolar range, and SF6 concentrations of the order of 10 microM were determined by 19F NMR signal integral measurements and used to quantify the affinity of CB for SF6. Integrals, which are usually not reliable for quantitative measurements in 129Xe NMR, were proven to be highly valuable for determining the affinity of alphaCD for SF6 as well. Most interestingly, heteronuclear Overhauser effect measurements allow to selectively highlight the 1H of a SF6 binding site according to the 19F-1H proximity and were used to characterize the inclusion complex formed with alphaCD.

Microwave absorption properties of double-layer absorbers made of NiCoZn ferrites and hollow glass microspheres electroless plated with FeCoNiB

Amorphous FeCoNiB coatings were deposited by an electroless plating technique on the hollow glass microspheres. NiCoZn spinel ferrites sintered show two dispersion peaks (1.81 and 6.98 GHz). By fitting its permeability dispersion spectra, the one at low frequency is believed to be due to the domain wall movement mechanism, the other one is due to the spin rotation mechanism. Used in a single-layer absorber structure, neither the hollow glass microspheres coated nor the NiCoZn could meet the demand of light weight. However, if a double-layer absorber structure is used, not only the total weight of an absorber is reduced, but also the microwave absorption performance is enhanced.

Spin Chemical Control of Photoinduced Electron-Transfer Processes in Ruthenium(II)-Trisbipyridine-Based Supramolecular Triads: 2. The Effect of Oxygen, Sulfur, and Selenium as Heteroatom in the Azine Donor

Nanosecond time-resolved absorption studies in a magnetic field ranging from 0 to 2.0 T have been performed on a series of covalently linked donor(PXZ)-Ru(bipyridine)3-acceptor(diquat) complexes (D-C2+-A2+). In the PXZ moiety, the heteroatom (X = O (oxygen), T (sulfur), and S (selenium)) is systematically varied to study spin-orbit coupling effects. On the nanosecond time scale, the first detectable photoinduced electron-transfer product after exciting the chromophore C2+ is the charge-separated (CS) state, D+-C2+-A+, where an electron of the PXZ moiety, D, has been transferred to the diquat moiety, A2+. The magnetic-field-dependent kinetic behavior of charge recombination (monoexponential at 0 T progressing to biexponential for all three complexes with increasing field) can be quantitatively modeled by the radical pair relaxation mechanism assuming creation of the CS state with pure triplet spin correlation (3CS). Magnetic-field-independent contributions to the rate constant kr of T+/- --> (T0,S) relaxation are about 4.5 x 10(5) s-1 for DCA-POZ and -PTZ (due to a vibrational mechanism) and 3.5 x 10(6) s-1 for DCA-PSZ (due to spin rotational mechanism). Recombination to the singlet ground state is allowed only from the 1CS spin level; spin-forbidden recombination from 3CS seems negligible even for DCA-PSZ. The field dependence of kr (field-dependent recombination) can be decomposed into the contributions of various relaxation mechanisms. For all compounds, the electron spin dipolar coupling relaxation mechanism dominates the field dependence of tau(slow) at fields up to about 100 mT. Spin relaxation due to the g-tensor anisotropy relaxation mechanism accounts for the field dependence of tau(slow) for DCA-PSZ at high fields. For the underlying stochastic process, a very short correlation time of 2 ps has to be assumed, which is tentatively assigned to a flapping motion of the central, nonplanar ring in PSZ. Finally, it has been confirmed by paramagnetic quenching (here Heisenberg exchange) experiments of the magnetic-field effects with TEMPO that all magnetic-field dependencies observed with the present DCA-PSZ systems are indeed due to the magnetic-field dependence of spin relaxation.

Nuclear Relaxation of H2 and H2@C60 in Organic Solvents

The 1H nuclear spin-lattice relaxation time (T1) of H2 and H2@C60 in organic solvents varies with solvent, and it varies proportionally for H2 and for H2@C60. Since intermolecular magnetic interactions are ruled out, the solvent must influence the modulating processes of the relaxation mechanisms of H2 both in the solvent cage and inside C60. The temperature dependence of T1 also is very similar for H2 and H2@C60, T1 going through a maximum by varying the temperature in solvents which allow a wide range of temperatures to be explored. This behavior is attributed to the presence of dipolar and spin-rotation mechanisms which have an opposite dependence on temperature.

Full multinuclear magnetic resonance analysis of 2,4‐dinitrofluorobenzene

AbstractThe complete assignment of the high‐resolution NMR spectra 2,4‐dinitrofluorobenzene was made, including the 1H, 13C, 15N, 17O and 19F nuclei. The 13C,19F, 13C,1H, 15N,19F and 15N,1H one‐bond and long‐range coupling constants were determinated and the signs were obtained by means of two‐dimensional correlation spectroscopy: 1H–1H‐COSY, 13C–1H‐COSY, 13C–1H‐COLOC and 1H–15N, 19F–15N and 19F–13C HMQC. The spin–lattice relaxation times of 13C revealed their anisotropy components and it was evident that the dipole–dipole contribution of fluorine was an efficient mechanism for C‐1 relaxation. The T1s of 1H agreed with the classical description: at low temperature the main contribution is dipole–dipole relaxation and at high temperature the relaxation is dominated by the spin–rotation mechanism. A linear relationship between δ13C(exp) and σC using GIAO (hybrid functional B3LYP) was found. 3J(13C, 1H) and the 1J(13C, 13C) have a relationship with the delocalization energies estimated by the NBO approach. Copyright © 2002 John Wiley &amp; Sons, Ltd.