Magnetic Relaxation Research Articles

Magnetic Resonance Relaxation in Heterogeneous Materials is Analogous to First-Order Chemical Reaction

AbstractBiological tissue, pharmaceutical tablets, wood, porous rocks, catalytic reactors, concrete, and foams are examples of heterogeneous systems that may contain one or several fluid phases. Fluids in such systems carry chemical species that may participate in chemical reactions in the bulk of a fluid, as homogeneous reactions, or at the fluid/fluid or fluid/solid interfaces, as heterogeneous reactions. Magnetic resonance relaxation measures the return of 1H nuclear magnetization in chemical species of these fluids to an equilibrium state in a static magnetic field. Despite the perceived difference between reaction–diffusion and relaxation–diffusion in heterogeneous systems, similarities between the two are remarkable. This work draws a close parallel between magnetic resonance relaxation–diffusion and chemical reaction–diffusion for elementary unitary reaction $${\text{A}}\to {\text{B}}$$ A → B in a dilute solution—both in heterogeneous systems. A striking similarity between the dimensionless numbers that characterize their relevant behavior is observed: the Damköhler number of the second kind $${{\text{Da}}}^{{\text{II}}}$$ Da II for reaction and the Brownstein–Tarr number $${{\text{BT}}}_{i}$$ BT i for relaxation. The new vision of analogy between reaction- and magnetic resonance relaxation–diffusion in heterogeneous systems encourages the exploitation of similarities between reaction and relaxation processes to noninvasively investigate the dynamics of chemical species and reactions. One such example of importance in chemical engineering is provided for solid–fluid reaction in packed beds.

Range and sensitivity of 17O nuclear spin-lattice relaxation as a probe of aqueous electrolyte dynamics.

The study of electrolytic solutions is of relevance in many research fields, ranging from biophysics, materials, and colloid science to catalysis and electrochemistry. The dependence of solution dynamics on the nature of electrolytes and their concentrations has been the subject of many experimental and computational studies, yet it remains challenging to obtain a full understanding of the factors that govern solution behavior. Here, we provide additional insights into the behavior of aqueous solutions of alkali chlorides by combining 17O relaxation data with diffusion and viscosity data and contrast their behavior with 1H nuclear magnetic resonance relaxation data. The main findings are that 17O relaxation correlates well with viscosity data but not with diffusion data, while 1H relaxation correlates with neither. Certain ionic trends match known ion-specific series behavior, especially at high concentrations. Notably, we also examine the ranges of the interactions and conclude that the majority of the effects are tied to local water reorientation dynamics.

Dual Structure of a Vanadyl-Based Molecular Qubit Containing a Bis(β-diketonato) Ligand.

We designed [VO(bdhb)] (1') as a new electronic qubit containing an oxovanadium(IV) ion (S = 1/2) embraced by a single bis(β-diketonato) ligand [H2bdhb = 1,3-bis(3,5-dioxo-1-hexyl)benzene]. The synthesis afforded three different crystal phases, all of which unexpectedly contain dimers with formula [(VO)2(bdhb)2] (1). A trigonal form (1h) with a honeycomb structure and 46% of solvent-accessible voids quantitatively transforms over time into a monoclinic solvatomorph 1m and minor amounts of a triclinic solventless phase (1a). In a static magnetic field, 1h and 1m have detectably slow magnetic relaxation at low temperatures through quantum tunneling and Raman mechanisms. Angle-resolved electron paramagnetic resonance (EPR) spectra on single crystals revealed signatures of low-dimensional magnetic behavior, which is solvatomorph-dependent, being the closest interdimer V···V separations (6.7-7.5 Å) much shorter than intramolecular V···V distances (11.9-12.1 Å). According to 1H diffusion ordered spectroscopy (DOSY) and EPR experiments, the complex adopts the desired monomeric structure in organic solution and its geometry was inferred from density functional theory (DFT) calculations. Spin relaxation measurements in a frozen toluene-d8/CD2Cl2 matrix yielded Tm values reaching 13 μs at 10 K, and coherent spin manipulations were demonstrated by Rabi nutation experiments at 70 K. The neutral quasi-macrocyclic structure, featuring nuclear spin-free donors and additional possibilities for chemical functionalization, makes 1' a new convenient spin-coherent building block in quantum technologies.

Magnetic short-range order and Griffiths-like phase in the S-1/2 spin-dimer ferromagnet BaCu(SeO3)2

The polycrystals of S = 1/2 spin-dimer compound BaCu(SeO3)2 have been synthesized by using solid-state reaction. Without long-range order, the magnetic susceptibility χ(T) curve presents two anomalies at T1 = 5 K and TG = 58 K due to antiferromagnetic (AFM) short-range order and short-range ferromagnetic (FM) correlations, respectively, which is further supported by the specific heat and electron spin resonance data. The high-temperature χ(T) curve follows the Curie-Weiss law with θCW = 11.3 K, showing the dominant intradimer FM interaction. The magnetization M(H) curve at 2 K is characteristic of an AFM-FM transition at 0.4 T, suggesting the weak interdimer AFM couplings. The density function theory calculations and quantum Monte Carlo simulations allow an estimation of the intradimer and interdimer exchanges with J1/kB = 39.09 K, J2/kB = −1.51 K, and J3/kB = −1.68 K. Interestingly, the χ−1(T) curve within θCW <T <TG deviates downward from paramagnetic Curie-Weiss behavior, mimicking the Griffiths-like phase. This is further supported by the ac magnetic susceptibility and magnetic relaxation measurements. The competing intradimer FM and interdimer AFM exchanges with a subtle ratio between them are proposed to be responsible for the formation of Griffiths-like phase.

Multienzyme-Mediated Dual-Channel Magnetic Relaxation Switching Taste Biosensor (D-MRSTB) for Simultaneous Detection of Umami Compounds and Synergistic Enhancement in Food.

Umami substances play a significant role in the evaluation of food quality, and their synergistic enhancement is of great importance in improving and intensifying food flavors and tastes. Current biosensors available for umami detection still confront challenges in simultaneous quantification of multiple umami substances and umami intensities. In this study, an innovative dual-channel magnetic relaxation switching taste biosensor (D-MRSTB) was developed for the quantitative detection of representative umami substances. The multienzyme signal of D-MRSTB specifically catalyzes the umami substances of interest to generate hydrogen peroxide (H2O2), which is then used to oxidate Fe2+ to Fe3+. Such a valence-state transition of paramagnetic ions was utilized as a magnetic relaxation signaling switch to influence the transverse magnetic relaxation time (T2) within the reaction milieu, thus achieving simultaneous detection of monosodium glutamate (MSG) and inosine 5'-monophosphate (IMP). The biosensor showed good linearity (R2 > 0.99) in the concentration range of 50-1000 and 10-1000 μmol/L, with limits of detection (LOD) of 0.61 and 0.09 μmol/L for MSG and IMP, respectively. Furthermore, the biosensor accurately characterized the synergistic effect of the mixed solution of IMP and MSG, where ΔT2 showed a good linear relationship with the equivalent umami concentration (EUC) of the mixed solution (R2 = 0.998). Moreover, the D-MRSTB successfully achieved the quantitative detection of umami compounds in real samples. This sensing technology provides a powerful tool for achieving the detection of synergistic enhancement among umami compounds and demonstrates its potential for application in the food industry.

Method to quickly estimate T1 value by suppressing spin exchange relaxation and magnetic field gradient relaxation in atomic sensors

The accuracy of atomic sensor is determined by the transverse nuclear spin relaxation time (T2). As the longitudinal nuclear spin relaxation time (T1) is the upper limit of T2, it becomes an important metric for evaluating the merits of alkali vapor cells. However, the conventional method for measuring T1 of pulse delay takes dozens of minutes, which will increase the effect of random errors during the testing process. In order to solve this problem, a method to quickly estimate the value of T1 is proposed by suppressing the influence of spin exchange relaxation and magnetic field gradient relaxation terms on T2. Experimental results indicate that the accuracy is maintained at above 95%, and the testing time is reduced to less than 5%.

Spintronic virtual neural network by a voltage controlled ferromagnet for associative memory

Recently, an associative memory operation by a virtual oscillator network, consisting of a single spintronic oscillator, was examined to solve issues in conventional, real oscillators-based neural networks such as inhomogeneities between the oscillators. However, the spintronic oscillator still carries issues dissipating large amount of energy because it is driven by electric current. Here, we propose to use a single ferromagnet manipulated by voltage-controlled magnetic anisotropy (VCMA) effect as a fundamental element in a virtual neural network, which will contribute to significantly reducing the Joule heating caused by electric current. Instead of the oscillation in oscillator networks, magnetization relaxation dynamics were used for the associative memory operation. The associative memory operation for alphabet patterns is successfully demonstrated by giving correspondences between the colors in a pattern recognition task and the sign of a perpendicular magnetic anisotropy coefficient, which could be either positive or negative via the VCMA effect.

Slow magnetic relaxation in a europium(II) complex.

Single-ion anisotropy is vital for the observation of Single-Molecule Magnet (SMM) properties (i.e., a slow dynamics of the magnetization) in lanthanide-based systems. In the case of europium, the occurrence of this phenomenon has been inhibited by the spin and orbital quantum numbers that give way to J = 0 in the trivalent state and the half-filled population of the 4f orbitals in the divalent state. Herein, by optimizing the local crystal field of a quasi-linear bis(silylamido) EuII complex, the [EuII(N{SiMePh2}2)2] SMM is described, providing an example of a europium complex exhibiting slow relaxation of its magnetization. This behavior is dominated by a thermally activated (Orbach-like) mechanism, with an effective energy barrier of approximately 8 K, determined by bulk magnetometry and electron paramagnetic resonance. Ab initio calculations confirm second-order spin-orbit coupling effects lead to non-negligible axial magnetic anisotropy, splitting the ground state multiplet into four Kramers doublets, thereby allowing for the observation of an Orbach-like relaxation at low temperatures.

Quenching luminescence, thermolysis and SMM behavior of new TbIII, EuIII, GdIII complexes with 4-nitro-N'-(pyridin-2-ylmethylene)benzohydrazide

The reaction of 4-nitro-N'-(pyridin-2-ylmethylene)benzohydrazide (HL) with Ln(OAc)3·4H2O in MeOH makes it possible to synthesize mononuclear complexes [Ln(L)2(OAc)(MeOH)]·2H2O (Ln = TbIII (1), EuIII (2) and GdIII (3)) with chelate acetate and L‒ anions. Compound 1 can be crystallized in reaction with molar ratio HL:Ln = 1:1, 2:1, 3:1, and we successfully synthesized complex with three chelate L anions [Tb(L)3]2·2MeOH·H2O (4) by interaction of TbCl3∙6H2O with deprotonated HL (HL:Ln = 3:1). Terbium(III) compound 1 starts to decompose at ∼323 K and becomes stable up to 552 K according to the STA. Compound 1 shows slow magnetic relaxation with parameters Δeff/kB = (6.75 ± 0.02) K, τ0 = (1.71 × 10−6±1 × 10−8) s. Complexes 1 and 2 exhibit only fluorescence and phosphorescence of the L‒. Ion-centered luminescence of the Tb3+ or Eu3+ ion is not observed. Using the tangent method at the high-energy edge of the phosphorescence spectrum of Gd3+, complex 3 T1 energy level of L‒ is estimated to be 19700 cm−1. Reasons of luminescence quenching are discussed. Structures of 1 and 4 were determined by single crystal X-ray diffraction, and compounds 1–3 were characterized by powder X-ray diffraction (PXRD).

Structural, magnetic, impedance and electric modulus response and dielectric relaxation in Co-doped inverse spinel [formula omitted] nanoferrite

In this research work, we report synthesis, structural, electric and magnetic properties of Cu1−XCoXFe2O4(x = 0.05, 0.10, 0.15, 0.20) nanoferrite. All the samples are synthesized using sol-gel auto-combustion method. X-ray diffraction patterns validate the formation of single phase tetragonal structure at room temperature for all the samples. Absence of secondary phases confirms the successful substitution of Cu2+ by Co2+ ions in CuFe2O4 matrix. Dielectric analysis reveals that all the materials exhibit remarkable single dielectric relaxation. The dielectric relaxation peaks are observed between 150–225 °C. In addition, Co-doped CuFe2O4 exhibit marked enhancement of dielectric constant value for potential technological applications. Further, the correlated barrier hopping (CBH) model well explains the conduction phenomena in all the samples. Activation energy values are analyzed by applying the Arrhenius equation. Impedance analysis indicates that both grain and grain boundary effects contributed the electrical response in the ferrites which is confirmed from the plot of Z″ vs. Z′. The bulk and grain boundary response are further determined by modeling the impedance data with an equivalent circuit. Modulus study confirms the existence of non-Debye type of relaxation in the synthesized ferrites. Magnetic study shows the improved value of magnetic parameters such as saturation magnetization (Ms), remanent magnetization (Mr) and coercive field (Hc).

Micromagnetic simulation of NdFeB considering spatial–temporal correction

Micromagnetic modeling, as a progressive numerical simulation method of magnetic research, can reveal the magnetization mechanism of materials while saving experimental costs. However, its application scale is limited by the enormous computational cost. Currently, micromagnetic simulations are mainly applied to calculate the magnetization of nanocrystalline magnets below the micrometer level. For larger magnets with grain sizes in the range of tens micrometers, such as sintered Nd-Fe-B magnets, this high-precision numerical calculation method may be less effective. To end this, this study proposes a nanocrystal-sized micromagnetic model, which is adjusted by fitting the magnetization relaxation time and intergranular coupling strength. Through incorporating time and spatial correction coefficients, it can calculate the magnetization behavior of large-grain magnets effectively. The thermal demagnetization process of sintered Nd-Fe-B magnets is further analyzed, and the micromagnetic simulation results are compared with the experimental results from temperature-controlled demagnetization experiments, which confirms the accuracy of the equivalent method. This research expands the research application scale of micromagnetic simulations and reveals the magnetization mechanism of sintered Nd-Fe-B magnets under thermal effects.

On creep of trapped flux near [formula omitted] in MgB2 and CaKFe4As4

We present flux creep data taken at different temperatures on single crystals of known, ambient pressure, superconductors, CaKFe4As4 and MgB2, taken using the protocol that is common for trapped flux measurements. Using our results, we show that the time dependence of the magnetic moment in H3S is remarkably similar to the magnetization relaxation rates observed in established superconductors at ambient pressure, where in the latter cases this can be unambiguously assigned to flux creep.

Signatures of nearly compensated magnetism and spin glass behavior in highly frustrated β-Mn-type Mn50Fe25+xAl25-x Heusler alloys.

The present study examines the effect of Fe/Al concentration on the structural and magnetic properties of Mn-rich Mn50Fe25+xAl25-x (x = 5, 10, 15) Heusler alloys through x-ray diffraction, temperature- and field-dependent DC magnetization, thermoremanent magnetization, magnetic memory effect, AC susceptibility measurements, and DFT calculations. The samples crystallize in a cubic β-Mn structure. The trend shows a reduction in lattice parameters (unit cell volume) with the increasing Fe proportion. These alloys exhibit strong antiferromagnetic interactions with large frustration parameters, indicating the presence of competing magnetic interactions. The DC magnetization data reveal spin glass-like features with a peak at spin glass freezing temperature (Tf). The observation of bifurcation in temperature-dependent zero-field-cooled and field-cooled magnetization curves, exponential dependence of the temperature variation of remanence and coercivity, magnetic relaxation, and magnetic memory effect below Tf support the spin-glass character of these alloys. The frequency dependence of Tf is also examined in the context of dynamic scaling laws, such as the Vogel-Fulcher law and critical slowing down model, which further supports the presence of spin glass behavior. In the theoretical DFT calculations, the electronic structure is found to be metallic and similar for both spin projections. Moreover, the antiferromagnetic arrangement of the magnetic moments, in line with the experimental observations, is stabilized by exchange interactions, resulting in an almost compensated total magnetic moment of 0.02-0.38µB/f.u. This is probably caused by the frustrated structure and non-stoichiometric compositions of Mn50Fe25+xAl25-x.

Can Iron-Porphyrins Behave as Single-Molecule Magnets?

The study of magnetic properties, especially the magnetic anisotropy of iron-porphyrin complexes employing multiconfigurational methods, is quite challenging due to many strongly correlated electrons in nearly degenerate orbitals. However, a prerequisite for observing the magnetic anisotropy and slow magnetization relaxation, the zero-field splitting parameter, D, was experimentally observed decades ago for halide-based axially ligated penta-coordinate Fe(III)-porphyrins. In these complexes, the signs of D were reported mostly as positive; in a few cases, inconclusive signs of the D parameter were also mentioned. However, no ab initio calculations have been reported to shed light on this. Deciphering the electronic structure of these penta-coordinated complexes employing the complete active space self-consistent field method and N-electron valence second-order perturbation theory, we confirm the positive D values. However, a negative D value is highly desired to observe the single-molecule magnet properties without an external magnetic field, which we observed in the Fe(II)-porphyrin complexes with axial imidazole ligands instead of halide ligands. The detailed analysis of the multireference wave functions unravels the role of axial ligands in determining the sign and magnitude of the D parameters.

Key Contributors to Signal Generation in Frequency Mixing Magnetic Detection (FMMD): An In Silico Study.

Frequency mixing magnetic detection (FMMD) is a sensitive and selective technique to detect magnetic nanoparticles (MNPs) serving as probes for binding biological targets. Its principle relies on the nonlinear magnetic relaxation dynamics of a particle ensemble interacting with a dual frequency external magnetic field. In order to increase its sensitivity, lower its limit of detection and overall improve its applicability in biosensing, matching combinations of external field parameters and internal particle properties are being sought to advance FMMD. In this study, we systematically probe the aforementioned interaction with coupled Néel-Brownian dynamic relaxation simulations to examine how key MNP properties as well as applied field parameters affect the frequency mixing signal generation. It is found that the core size of MNPs dominates their nonlinear magnetic response, with the strongest contributions from the largest particles. The drive field amplitude dominates the shape of the field-dependent response, whereas effective anisotropy and hydrodynamic size of the particles only weakly influence the signal generation in FMMD. For tailoring the MNP properties and parameters of the setup towards optimal FMMD signal generation, our findings suggest choosing large particles of core sizes dC>25 nm with narrow size distributions (σ<0.1) to minimize the required drive field amplitude. This allows potential improvements of FMMD as a stand-alone application, as well as advances in magnetic particle imaging, hyperthermia and magnetic immunoassays.

Supramolecular assembly, structure, magnetic property, and proton conductivity of a nickel(II) hydrogen-bonded organosulfonate framework

A three-dimensional nickel(II) hydrogen-bonded organic framework (NiHOF), formulated as [Ni(H2O)2(EtOH)2(MeCN)2][nds] (NiHOF-HGNU-2, H2nds = 1,5-Naphthalenedisulfonic acid, HGNU = Huanggang Normal University), was synthesized and magnetically and electrically characterized. Single-crystal X-ray diffraction (SC-XRD) analysis revealed that extensive hydrogen bonding interactions formed between the [Ni(H2O)(EtOH)(MeCN)]2+cations and organodisulfonate anions nds2−, leading to a highly hydrogen-bonded network. Variable-temperature SC-XRD and thermogravimetric analysis both reveal the crystalline sample of NiHOF-HGNU-2 can be thermally stable up to 400 K. Magnetic investigations reveal the uniaxial magnetic anisotropy (D = -9.87 cm−1) of the distorted octahedral Ni2+ ions of NiHOF-HGNU-2 without slow magnetic relaxation. Alternating current impedance spectroscopy indicate NiHOF-HGNU-2 exhibits temperature- and humidity-dependent proton conduction behavior with the highest measured conductivity reaching 1.15 × 10−4 S cm−1 at 85 °C and 98 % relative humidity, suggesting a supramolecular proton conductor of the NiHOF-HGNU-2. The forgoing results not only provide a new Ni-based proton conductor but also an organodisulfonate strategy for building supramolecular proton-conducting materials.

Designing Sustainable Hydrophilic Interfaces via Feature Selection from Molecular Descriptors and Time-Domain Nuclear Magnetic Resonance Relaxation Curves.

Surface modification using hydrophilic polymer coatings is a sustainable approach for preventing membrane clogging due to foulant adhesion to water treatment membranes and reducing membrane-replacement frequency. Typically, both molecular descriptors and time-domain nuclear magnetic resonance (TD-NMR) data, which reveal physicochemical properties and polymer-chain dynamics, respectively, are required to predict the properties and understand the mechanisms of hydrophilic polymer coatings. However, studies on the selection of essential components from high-dimensional data and their application to the prediction of surface properties are scarce. Therefore, we developed a method for selecting features from combined high-dimensional molecular descriptors and TD-NMR data. The molecular descriptors of the monomers present in polyethylene terephthalate films were calculated using RDKit, an open-source chemoinformatics toolkit, and TD-NMR spectroscopy was performed over a wide time range using five-pulse sequences to investigate the mobility of the polymer chains. The model that analyzed the data using the random forest algorithm, after reducing the features using gradient boosting machine-based recursive feature elimination, achieved the highest prediction accuracy. The proposed method enables the extraction of important elements from both descriptors of surface properties and can contribute to the development of new sustainable materials and material-specific informatics methodologies encompassing multiple information modalities.

Ligand‐field effect to harness the magnetic anisotropy in a series of mixed valence Co (III)–Co (II) dinuclear complexes

Three mixed valence dinuclear Co (III)–Co (II)‐based complexes having general formulae of [CoIICoIII (HL2)2(L1)] [L1H = 2‐hydroxy‐1‐naphthaldehyde (1), o‐vanillin (2), and salicylaldehyde (3)] have been synthesized successfully using Schiff base (LH4) ligand. The complexes were characterized by single‐crystal XRD, powder XRD, IR, and UV–Vis analyses. The CoII ion with elongated octahedral geometry conferred significant magnetic anisotropy with D values being 64.0(8), 71.1(7), and 52.1(3) cm−1 for 1, 2, and 3, respectively. These complexes exhibited single‐molecule magnet behavior with magnetic relaxation occurring mainly through Raman for 1 and 3 whereas direct and Raman for complex 2. The analysis of the static and dynamic magnetic properties was further supported by theoretical calculations using CASSCF/DLPNO‐NEVPT2.

Oxygen-Donor Metalloligands Induce Slow Magnetization Relaxation in Zero Field for a Cobalt(II) Complex with {CoO4} Motif.

Most 3d metal-based single-molecule magnets (SMMs) use N-ligands or ligands with even softer donors to impart a particular coordination geometry and increase the zero-field splitting parameter |D|, while complexes with hard O-donor ligands showing slow magnetization relaxation are rare. Here, we report that a diamagnetic NiII complex of a tetradentate ligand featuring two N-heterocyclic carbene and two alkoxide-O donors, [LO,ONi], can serve as a {O,O'}-chelating metalloligand to give a trinuclear complex [(LO,ONi)Co(LO,ONi)](OTf)2 (2) with an elongated tetrahedral {CoIIO4} core, D = -74.3 cm-1, and a spin reversal barrier Ueff = 86.9 cm-1 in the absence of an external dc field. The influence of diamagnetic NiII on the electronic structure of the {CoO4} unit in comparison to [Co(OPh)4]2- (A) has been probed with multireference ab initio calculations. These reveal a contrapolarizing effect of the NiII, which forms stronger metal-alkoxide bonds than the central CoII, inducing a change in ligand field splitting and a 5-fold increase in the magnetic anisotropy in 2 compared to A, with an easy magnetization axis along the Ni-Co-Ni vector. This demonstrates a strategy to enhance the SMM properties of 3d metal complexes with hard O-donors by modulating the ligand field character via the coordination of diamagnetic ions and the benefit of robust metalloligands in that regard.

Mechanism analysis of rheological properties of 3D printed steel slag cementitious composite based on low field nuclear magnetic relaxation test

Rheological properties play a crucial role in characterizing 3D printed cement-based materials. To further investigate the mechanism behind rheological evolution, this study employs low-field NMR relaxation time measurement to characterize the microstructure evolution of 3D printed steel slag cementitious material within the first 6 hours. This is combined with rheological parameters to explore the relationship between the mixture's rheological properties and pore microstructure over time. The results demonstrate that relaxation time effectively represents the temporal characteristics of rheological parameters, while pore throat distribution (0–0.1μm) exhibits a positive correlation with plastic viscosity. Low-field NMR relaxation characteristics can effectively describe early properties of 3D printed cementitious materials and provide valuable data support for future exploration of non-destructive testing during early stages.