Dynamic Magnetic Behavior Research Articles

Dynamic magnetic behaviors of a double-layer core/shell graphene nanoribbon in a time-dependent magnetic field

Using Monte Carlo simulation, we examine the dynamic magnetic properties of a double-layer core/shell graphene nanoribbon which is subjected to a time-dependent oscillating magnetic field. The present system can display unique magnetic behaviors and abundant phase diagrams under the influence of various physical parameters including the exchange couplings, time-dependent oscillating magnetic field and temperature. We find that the exchange coupling can promote the unification of the spin direction and the stability of the system. The bias magnetic field and the amplitude of oscillating magnetic field have opposite effects on the phase transition temperature. In addition, much effort is also dedicated to the hysteresis behaviors of the system. Under certain parameters, the system can present interesting multi-cycle hysteresis behaviors which come from competition among several parameters.

Time-resolved imaging of an operating hard-disk-drive write head using nano-beam x-ray magnetic circular dichroism

We studied the dynamic magnetization behavior of a hard-disk-drive (HDD) write head by using nano-beam x-ray magnetic circular dichroism (XMCD). The write head was operated by applying a square-wave write current with a frequency of 211.9 MHz to the coil of the write head, which was in synchronization with the fivefold frequency of the x-ray pulses. Snapshot images of the magnetization on the air-bearing surface of the write head were obtained with spatial and time resolutions of 100 nm and 50 ps, respectively, and temporal changes in the magnetization of the main pole and the shield were observed. When a square-wave write current with a transition time of 0.2 ns was applied, the magnetization reversal of the main pole was completed in 0.7 ns, and this reversal time was determined by the dynamic property of the write head. During the main pole reversal, the shield area showed spatially non-uniform magnetization patterns, and its response was slower than that of the main pole. These results show that the XMCD measurement setup developed in this study is a powerful tool for understanding the dynamic behavior of an HDD write head and contributes to the development of higher capacity HDDs.

Experimental exploration of dynamic phase transitions and associated metamagnetic fluctuations for materials with different Curie temperatures.

We study dynamic magnetic behavior in the vicinity of the dynamic phase transition (DPT) for a suitable series of samples that have different Curie temperatures T_{C}, which thus enables us to experimentally explore the role of the reduced temperature T/T_{C} in the DPT. For this purpose, we fabricate Co_{1-x}Ru_{x} epitaxial thin films with uniaxial in-plane anisotropy by means of sputter deposition in the concentration range 0.0≤x≤0.26. All samples are ferromagnetic at room temperature, exhibit an abrupt magnetization reversal along their easy axis, and represent a unique T_{C} and thus T/T_{C} ratio according to their Ru concentration. The dynamic magnetic behavior is measured by using an ultrasensitive transverse magneto-optical detection method and the resulting dynamic states are explored as a function of the applied magnetic field amplitude H_{0} and period P, as well as an additional bias field H_{b}, which is the conjugate field of the dynamic order parameter Q. Our experimental results demonstrate that the qualitative behavior of the dynamic phase diagram is independent of the T/T_{C} ratio and that for all T/T_{C} values we observe metamagnetic anomalies in the dynamic paramagnetic state, which do not exist in the corresponding thermodynamic phase diagram. However, quantitatively, these metamagnetic anomalies are very strongly dependent on the T/T_{C} ratio, leading to an about 20-fold increase of large metamagnetic fluctuations in the paramagnetic regime as the T/T_{C} ratio increases from 0.37 to 0.68. Also, the phase space range in which these anomalous metamagnetic fluctuations occur extends closer and closer to the critical point as T/T_{C} increases.

The Influence of Halide Substituents on the Structural and Magnetic Properties of Fe6Dy3 Rings.

We report the synthesis and magnetic properties of three new nine-membered Fe(III)-Dy(III) cyclic coordination clusters (CCCs), with a core motif of [Fe6Dy3(μ-OMe)9(vanox)6(X-benz)6] where the benzoate ligands are substituted in the para-position with X = F (1), Cl (2), Br (3). Single crystal X-ray diffraction structure analyses show that for the smaller fluorine or chlorine substituents the resulting structures exhibit an isostructural Fe6Dy3 core, whilst the 4-bromobenzoate ligand leads to structural distortions which affect the dynamic magnetic behavior. The magnetic susceptibility and magnetization of 1-3 were investigated and show similar behavior in the dc (direct current) magnetic data. Additional ac (alternating current) magnetic measurements show that all compounds exhibit frequency-dependent and temperature-dependent signals in the in-phase and out-of-phase component of the susceptibility and can therefore be described as field-induced SMMs. The fluoro-substituted benzoate cluster 1 shows a magnetic behavior closely similar to that of the corresponding unsubstituted Fe6Dy3 cluster, with Ueff = 21.3 K within the Orbach process. By increasing the size of the substituent toward 4-chlorobenzoate within 2, an increase of the energy barrier to Ueff = 36.1 K was observed. While the energy barrier becomes higher from 1 to 2, highlighting that the introduction of different substituents on the benzoate ligand in the para-position has an impact on the magnetic properties, cluster 3 shows a significantly different SMM behavior where Ueff is reduced in the Orbach regime to only 4.9 K.

Anomalous fractional magnetic field diffusion through cross-section of a massive toroidal ferromagnetic core

Toroidal massive ferromagnetic cores are used in a wide range of electromagnetic applications, such as current sensors, inductances, static converters and filters. Growing interest exists in the industrial field with regards simulation tools to reduce experimental campaigns and improve product knowledge and performance. Accurate simulation results require a consideration of precise electromagnetic laws, such as the exact non-linear magnetic behavior of toroidal magnetic cores. Under the influence of an external surface magnetic field that was created by a surrounding coil, the local magnetic state through a ferromagnetic core cross-section was ruled by a combination of magnetic domain kinetics and external magnetic field diffusion. Conventional methods to simulate magnetic behavior are based on a separation of magnetic contributions, where microscopic Eddy currents from domain wall motions and macroscopic currents from external magnetic field variations are considered separately. This separation is artificial, because both loss mechanisms occur simultaneously and interact. In this study, an alternative solution was proposed through the resolution of a two-dimensional anomalous fractional magnetic field diffusion. The fractional order constitutes an additional degree of freedom in the simulation scheme, which can be identified by comparison with the experimental results. By adjusting this order, accurate local and global simulation results can be obtained on a broad frequency bandwidth and allow for the precise prediction of the dynamic magnetic behavior of a toroidal massive magnetic core.

Magnetic Field-Induced Recoverable Dynamic Morphological Change of Gallium-Based Liquid Metal

We report magnetic field-driven dynamic morphological change of a liquid metal droplet: deformation and recovery; separation and merge. Low melting, non-toxic gallium-based liquid metal has been widely investigated due to its material properties and thus utilized to various applications. Morphological change of the liquid metal in required to tune characteristics of application. In order to enable the liquid metal to be non-wettable and magnetically controllable, we coated the surface with ferromagnetic iron (Fe) particles using hydrochloric acid (HCl) solution resulting in a magnetic liquid metal marble. With and without magnetic field, Fe particles-coated magnetic liquid metal marble was deformed and recovered readily. Against $\sim 8~\mu \text{L}$ magnetic liquid metal marble, depending on the coated Fe particles mass, the shape deformation under magnetic field was changed: conventional (Fe $\geqq ~4$ mg) wetting shape. Accordingly, the deformability and recovery time of the magnetic liquid metal marble were varied. With an applied magnetic field, one marble was readily separated into 2, 3, and 4 marbles. Due to re-oxidation of the magnetic liquid metal marble surface, we treated the marble with HCl solution and vapor. Split and merge occurred depending on treatment time of HCl solution or vapor. Finally, we demonstrated magnetic field-based dynamic behavior which is reversible. [2020-0218]

Assessment of differential magnetic susceptibility in nanoparticles: Effects of changes in viscosity and immobilisation

The nonlinear magnetic behaviour of superparamagnetic iron-oxide nanoparticles (SPIONs) has attracted interest as a valuable feature for upcoming medical applications. Injecting SPIONs into the human body affects their magnetic properties through the formation of protein corona or cell immobilisation. It is therefore important to study the effects of environmental changes on the magnetic susceptibility of SPIONs. A superparamagnetic quantifier (SPaQ) is used here to assess the differential magnetic susceptibility of three commercially available SPIONs: Synomag®, Resovist® and Sienna+®. The following experiments were carried out to mimic the influence of the biological environment on the magnetic responses of SPIONs: (i) varying the viscosity of the medium; and (ii) immobilising the nanoparticles by freeze-drying. Differential magnetisation curves as a function of the applied magnetic field were visualised to reveal the dynamic magnetic behaviour of SPIONs in both experiments. Synomag® displayed the lowest decrease (~5%) in differential magnetic susceptibility compared to Resovist® (~33%) and Sienna+® (~21%), for a change from water to a high-viscosity fluid. Although Synomag® showed a clear drop in differential magnetic susceptibility (~58%) after freeze-drying, it still appears to be a promising candidate for clinical applications due to its low sensitivity to changes in viscosity.

Dynamic magnetic hysteresis loop behaviors of a mixed spin (2, 5/2) Ising model on two interpenetrating square lattices

We investigate dynamic magnetic hysteresis loop (DMHL) behaviors of a mixed spin (2, 5/2) Ising model on two interpenetrating square lattices under an oscillating magnetic field within the effective-field theory based on Glauber–type stochastic dynamics. We study the DMHL properties for various values of reduced temperatures (T/zJ), crystal-field interaction (D/zJ) and frequency () of the magnetic field. We also examine T/zJ, D/zJ and dependences of the coercive fields (CFs) and remanent magnetizations (RMs). We found that for very low and high values of T/zJ and D/zJ, the hysteresis loop area is narrower and thinner that correspond soft magnets that desirable for transformers and motor cores and AC applications. We observed that for high values of the hysteresis loop areas are wide and big that corresponds hard magnets which can be useful for permanent magnets, magnetic recording, small motors and magnetic locks. We also found that the DMHLs, CFs and RMs behaviors are in quantitatively good agreement with some theoretical for Ising systems and experimental works for magnetic materials, such as cobalt films, Fe films and some magnetic nanomaterials.

Initial interaction of citrate-coated iron oxide nanoparticles with the glycocalyx of THP-1 monocytes assessed by real-time magnetic particle spectroscopy and electron microscopy

Interaction with biological material can alter physicochemical parameters of magnetic nanoparticles and might thereby change their magnetic behavior with potentially important implications for various nanoparticle applications. Little is known about changes of the magnetic behavior that occur during the initial phase of cell binding and uptake. We investigate the magnetic behavior of very small superparamagnetic iron-oxide nanoparticles (VSOP) during initial contact with THP-1 monocytes. We combine real-time magnetic particle spectroscopy (MPS), a fast and sensitive method for specific detection of magnetic nanoparticles in biological specimen with high-pressure-freezing/freeze-substitution transmission electron microscopy (HPF/FS-TEM), enabling us to generate snapshots of the interaction of VSOP with the cellular glycocalyx. MPS reveals significant changes of the dynamic magnetic behavior within seconds after VSOP injection into monocyte suspensions that correlate with the formation of nanoparticle clusters in the glycocalyx. The combination of real-time MPS and HPF/FS-TEM provides an ideal platform to analyze magnetic behaviors of nanoparticles upon interaction with cells and tissues.

Tuning Magnetization Dynamics with Strong Spin-Orbit Coupling in Transition-Metal Dichalcogenide/ Co - Fe - B Heterostructures

Spintronic materials with two-dimensional (2D) transition-metal dichalcogenide (TMD)/ferromagnet (FM) interfaces have received a great deal of interest recently due to strong modulation of the magnetic properties, which provide attractive opportunities for magnetic information storage. Here, we demonstrate the strong spin-orbit coupling (SOC) effect and great interfacial tuning of magnetization dynamics in $M{X}_{2}$/$\mathrm{Co}\text{\ensuremath{-}}\mathrm{Fe}\text{\ensuremath{-}}\mathrm{B}$ thin films by means of a time-resolved magneto-optical Kerr approach, where M is chosen as $\mathrm{Mo}$ or $\mathrm{W}$ and X is $\mathrm{S}$ or $\mathrm{Se}$. The significant drop of demagnetization time, ${\ensuremath{\tau}}_{m}$, and increase of magnetic damping factor, ${\ensuremath{\alpha}}_{s}$, clearly highlight the presence of high interfacial SOC strength in just one monolayer of ${\mathrm{Mo}\mathrm{S}}_{2}$. Compared with the single $\mathrm{Co}\text{\ensuremath{-}}\mathrm{Fe}\text{\ensuremath{-}}\mathrm{B}$ film, the precession frequency, f, is lowered after inserting a $M{X}_{2}$ layer, suggesting a reduction of the effective magnetization, $4\ensuremath{\pi}{M}_{\mathrm{eff}}$, originating from the interfacial d-d hybridization effect. The role of SOC strength on ${\ensuremath{\tau}}_{m}$, ${M}_{\mathrm{eff}}$, and ${\ensuremath{\alpha}}_{s}$ is confirmed by using different TMD materials, and thus, demonstrates that the element M plays a dominant role. The samples with ${\mathrm{WS}}_{2}$ or ${\mathrm{W}\mathrm{Se}}_{2}$ have much shorter ${\ensuremath{\tau}}_{m}$, smaller ${M}_{\mathrm{eff}}$, and larger ${\ensuremath{\alpha}}_{s}$ values due to the strong SOC interaction of heavier atoms. The observed efficient control of dynamic magnetic behavior will further promote the development of TMD/FM materials for practical spintronic applications with ultrafast manipulation speed and low energy consumption.

Identification and analysis of static and dynamic magnetization behavior sensitive to surface laser treatments within the electromagnetic field diffusion inside GO SiFe electrical steels

Surface laser treatment of soft magnetic materials, such as GO SiFe electrical steels, is mainly used to reduce iron losses by modifying the static and the dynamic magnetic properties. Laser treatment effect on mesoscopic electromagnetic properties of soft magnetic materials is presented. An experimental procedure using the Single Sheet Tester is performed on a magnetized sheet with specific exciting induction level and frequency. Transient average magnetic flux density through the sample cross-section and its corresponding applied magnetic field are measured. Data are identified in the time-domain with numerical results obtained by solving the diffusion equation using a 1-D discretization approach. The identification strategy requires a material law that includes both non-linear static and dynamic properties and describes the magnetic behavior due to domains and walls dynamics. Next, parametric and physical studies are performed on materials submitted to different laser treatments in order to determine and interpret their effects on the identified magnetic properties and the time response in the sheet’s depth. The results show that the static and the dynamic properties can be simultaneously improved. This analysis help to understand the impact of laser treatments on the static and the dynamic behaviour in order to improve the material magnetic performances within magnetic circuits inside electrical machines and transformers.

Cellular uptake of magnetic nanoparticles imaged and quantified by magnetic particle imaging

Magnetic particle imaging (MPI) is a non-invasive, non-ionizing imaging technique for the visualization and quantification of magnetic nanoparticles (MNPs). The technique is especially suitable for cell imaging as it offers zero background contribution from the surrounding tissue, high sensitivity, and good spatial and temporal resolutions. Previous studies have demonstrated that the dynamic magnetic behaviour of MNPs changes during cellular binding and internalization. In this study, we demonstrate how this information is encoded in the MPI imaging signal. Through MPI imaging we are able to discriminate between free and cell-bound MNPs in reconstructed images. This technique was used to image and quantify the changes that occur in-vitro when free MNPs come into contact with cells and undergo cellular-uptake over time. The quantitative MPI results were verified by colorimetric measurements of the iron content. The results showed a mean relative difference between the MPI results and the reference method of 23.8% for the quantification of cell-bound MNPs. With this technique, the uptake of MNPs in cells can be imaged and quantified directly from the first MNP cell contact, providing information on the dynamics of cellular uptake.

Magnetic softness, dynamic magnetization, and relaxation behavior of FeSiBC amorphous alloys

The variation of dynamic coercivity, core loss, permeability (μ′), and relaxation behavior with annealing temperature, frequency as well as magnetic field magnitude (Hm) for the FeSiBC amorphous alloy was systematically studied. It can be found that the dynamic coercivity (Hcd) of 6.2 A/m at 1.0 T and 50 Hz is much larger than the static coercivity (Hcs) of 1.7 A/m for the optimally annealed Fe78Si8B13C1 alloy. The increase of Hcd with the increases in frequency can be ascribed to the difficulty of domain wall motion and magnetization rotation as frequency elevates. The dynamic magnetization analysis reveals that μ′ goes up and attains a peak value as Hm increases to about 25 A/m in the low frequency range, while the μ′ does not depend on Hm in the high frequency range (f > 10 kHz). In addition, the change of magnetic relaxation time with annealing temperature and filed magnitude is discussed.

A Frequency-Dependent Scalar Magneto-Elastic Hysteresis Model Derived Using Multi-Scale and Jiles–Atherton Approaches

The effects of mechanical stress on static and dynamic (frequency-dependence) magnetic behaviors of soft magnetic materials have to be modeled. A scalar static magneto-elastic hysteresis model is proposed which combines a simplified version of a multi-scale approach and the Jiles-Atherton (JA) model. The magneto-elastic hysteresis model is extended to include dynamic losses using the field separation approach. The effect of stress on dynamic loss components, particularly on the excess loss, is approximated using an exponential function. The model is validated with measured dynamic hysteresis loops over a frequency range of up to 1 kHz and uniaxial mechanical loading up to 50 MPa (both compressive and tensile stresses). The proposed model still preserves its simplicity and inverse form representation, which makes it quite amenable to numerical implementations. The approach can be applied to model magneto-elastic effects in the elastic range.

Modulating magnetic dynamics through tailoring the terminal ligands in Dy2 single-molecule magnets.

Complexation of dysprosium(iii) ions with a multidentate hydrazone ligand, N-[(E)-pyridin-2-ylmethylideneamino]pyridine-2-carboxamide (L), in the presence of different β-diketonate coligands, leads to the formation of two novel DyIII dimers, with formulas Dy2(BTFA)4(L)2 (1) and Dy2(TTA)4(L)2 (2) (BTFA = 3-benzoyl-1,1,1-trifluoroacetone and TTA = 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionate). They exhibit slightly different coordination geometries around DyIII centers and discrepant binuclear motifs - as a result of altering the β-diketonate coligands - which has an impact on the magnetic interactions between metal centers, the local tensor of anisotropy on each DyIII site and their relative orientations, therefore contributing to distinct magnetization dynamics. Compared to 2, complex 1 exhibits a more significant slow magnetic relaxation of SMM behavior in the absence of a dc field. The QTM effect is effectively repressed under a static field, resulting in the energy barriers of 57 K for 1 and 38 K for 2. Ab initio calculations clarify that, strong single-ion magnetic anisotropies exist in both complexes, whereas intermetallic ferromagnetic interaction and antiferromagnetic interaction are observed in 1 and 2, respectively, therefore resulting in dissimilar magnetization dynamics.

Regulating the magnetic skyrmion in a confined nanochannel under a gradient magnetic field

A magnetic skyrmion could be endowed with various dynamic magnetic configurations and behaviors. By artificially generating a gradient magnetic field in a confined nanochannel, we have shown the magnetic dynamics of an isolated skyrmion, achieving the coexistence of moving and breathing modes. Such a phenomenon has been proven to be not only correlated to the gradient strength of a magnetic field, but also depends on the Dzyaloshinskii–Moriya interaction. By increasing the magnetic field gradient up to 0.1 mT nm−1, the skyrmion can effectively overcome the skyrmion Hall effect, and meanwhile generate a breathing mode during the motion process under MFG = 1.0 mT nm−1 and DMI = 2.8 mJ m−3. The present study could provide an alternative approach to regulate the skyrmion at micro/nanoscales by using a gradient magnetic field.

Exploring the magnetization dynamics, damping and anisotropy in engineered CoFeB/(Ag, Pt) multilayer films grown onto amorphous substrate

Abstract We investigate the magnetization dynamics in CoFeB/(Ag, Pt) multilayer films grown onto amorphous substrate engineered to have in-plane magnetic anisotropy and distinct effective damping parameter. We go beyond quasi-static magnetic properties and characterize the dynamic magnetic response by employing ferromagnetic resonance and magnetoimpedance measurements. The link between magnetic features and dynamic magnetic behavior allows us to identify the role of the effective damping parameter and of the magnetic anisotropy on the magnetoimpedance effect in multilayer films. In addition, we consider a theoretical approach to interpret the experimental data and also predict the magnetization dynamics in wider ranges of the explored parameters. From our results, we provide insights to tune the damping parameter and magnetic anisotropy in engineered multilayer films grown onto amorphous substrates.

Modulating dynamic magnetic behaviors of dysprosium(III) dinuclear compounds based on a Schiff base-like ligand by using two different β-diketone coligands

Two new Dy2 compounds, namely, [Dy2(acac)2(H2L)2(CH3O)2] (1) and [Dy2(beac)2(H2L)2(CH3O)2] (2) (Hacac = acetylacetone, Hbeac = 1-benzoylacetone, and H3L = 2-[(2-hydroxybenzhydrazide)methyl]-8-hydroxyquinoline), have been successfully synthesized, structurally and magnetically characterized. The single-crystal X-ray diffraction data show that both 1 and 2 are phenoxo-O-bridged dinuclear complexes with similar structures; each eight-coordinated center Dy(III) ion is connected by one bidentate β-diketone coligand, one CH3O− and two μ-O bridging Schiff base ligands. The magnetic investigation reveal that 1 and 2 exhibit different magnetic relaxation behaviors with the anisotropic barriers of 2.17 K (1) and 20.56 K (2). The different SMMs behaviors of 1 and 2 originate from the different coordination environments of the central Dy(III) ions with different β-diketone coligands.

Construction of Metallosupramolecular Coordination Complexes: From Lanthanide Helicates to Octahedral Cages Showing Single-Molecule Magnet Behavior.

The construction of metallosupramolecular complexes toward interesting topological structures is a critical challenge for chemists. The fluctuation in the synthetic strategy, by keeping the same metal-ligand combination, has proved a very significant approach to construct metallosupramolecular architectures. Herein, by varying the reaction conditions four new DyIII-supramolecular complexes based on a flexible dihydrazone ligand H2L (H2L = bis(2-hydroxy-3-methoxybenzylidene)adipohydrazide) in cooperation with different anions and solvents having formulas [Dy4L4(μ2-N3)2](NO3)2·6CH3OH·2H2O (1), [Dy8L8(μ2-CH3OH)4]Cl8·6CH3OH·14H2O (2), [Dy12L12(μ2-OH)2(OH)6(CH3O)2](NO3)2·2CH3OH·14H2O (3), and [Dy12L12(μ2-OH)2(NO3)2(OH)3(CH3O)](NO3)4·22H2O (4), have been successfully synthesized and their crystal structures confirmed by single crystal X-ray diffraction studies. The structural study reveals that 1 and 2 have quadruple-stranded helicate and dual triple-stranded helicate supramolecular structures, respectively, while 3 and 4 display "octahedron" cagelike supramolecular structures. The magnetic studies reveal that complexes 1-3 exhibit slow magnetic relaxation behavior, while complex 4 displays a series of typical frequency-dependent relaxation signals at 0 Oe applied dc field which is a rare case in polynuclear 4f single-molecule magnet (SMM) family to date. Interestingly, the distinct magnetic dynamic behavior was noticed for nearly isoskeletal complexes 3 and 4, which can be attributed to the modification of the coordination environment around DyIII ions.

Modulation of the magnetic anisotropy of octahedral cobalt(ii) single-ion magnets by fine-tuning the axial coordination microenvironment

The alteration of the axial N-donor ligands leads to two octahedral Co(ii) SIMs with varying easy-plane magnetic anisotropies and dynamic magnetic behaviors.