Ferromagnetic Slab Research Articles

Influence of demagnetizing effects on the magnetization curves of finite-size rectangular slabs

According to some recent studies, the magnetoresistance curves of ferromagnetic strip-shaped samples can significantly differ depending on whether the in-plane external applied magnetic field H is oriented in parallel to either the long or the short edge of the strip. To address this problem, in the present work magnetization curves M(H) were measured for similarly shaped samples with both magnetic field orientations used in the magnetoresistance measurements. It was found that the M(H) curves strongly depend on the saturation magnetization and shape of the samples as well as on the magnetic field orientations. For some samples with sufficiently large saturation magnetization, the effective demagnetizing factors could be deduced from the measured M(H) curves. By considering the investigated samples as a ferromagnetic slab, and approximating them with a general ellipsoid, the demagnetizing factors were calculated from known formulae and compared to the experimental values. A fairly good matching was observed, although the latter data were systematically slightly larger, certainly due to the not completely homogeneous magnetization within the rectangular slab as opposed to the case of a general ellipsoid. The differences in the M(H) curves for the two orientations of the magnetic field could be completely attributed to demagnetizing effects.

An Update to The Demagnetizing Factor Dataset Calculated for The General Ellipsoid by Osborn

The exact formulae for calculating the demagnetizing factors of a general ellipsoid along the three main axes a ≥ b ≥ c have been long known. According to these formulae, the demagnetizing factors depend only on the axial ratios b/a and c/a. Although the calculation of the demagnetizing factors is a straightforward task, the calculation itself is not a simple one. Therefore, tabular and graphical representations of these demagnetizing factor data have also been presented which can then be used for approximating the demagnetizing factors of a rectangular ferromagnetic slab with the same axial ratios. It turned out in our recent study, however, that, in some ranges of axial ratios (e.g., for very small c/a values), the available tables and graphs do not provide sufficient resolution for obtaining the demagnetizing factors with reasonable accuracy. It was decided to calculate these missing values, and they are presented here in both tabular and graphical form by giving instructions for how to obtain conveniently further interpolated data. In addition, the previous and current demagnetizing factor data have been replotted and fitted to a polynomial function with high accuracy. The functional form of these fitting polynomials is presented in a table for the whole range of the axial ratios b/a and c/a. By graphically displaying these functions, one can obtain, in a relatively simple manner, the demagnetizing factors of a general ellipsoid with known axial ratios without the need to directly calculate through the exact formulae. This may be helpful in obtaining a quick estimate for the demagnetizing factors of any rectangular ferromagnetic slab of interest.

Layered Semiconductor Cr0.32Ga0.68Te2.33 with Concurrent Broken Inversion Symmetry and Ferromagnetism: A Bulk Ferrovalley Material Candidate.

The valleytronic state found in group-VI transition-metal dichalcogenides such as MoS2 has attracted immense interest since its valley degree of freedom could be used as an information carrier. However, valleytronic applications require spontaneous valley polarization. Such an electronic state is predicted to be accessible in a new ferroic family of materials, i.e., ferrovalley materials, which features the coexistence of spontaneous spin and valley polarization. Although many atomic monolayer materials with hexagonal lattices have been predicted to be ferrovalley materials, no bulk ferrovalley material candidates have been reported or proposed. Here, we show that a new non-centrosymmetric van der Waals (vdW) semiconductor Cr0.32Ga0.68Te2.33, with intrinsic ferromagnetism, is a possible candidate for bulk ferrovalley material. This material exhibits several remarkable characteristics: (i) it forms a natural heterostructure between vdW gaps, a quasi-two-dimensional (2D) semiconducting Te layer with a honeycomb lattice stacked on the 2D ferromagnetic slab comprised of the (Cr, Ga)-Te layers, and (ii) the 2D Te honeycomb lattice yields a valley-like electronic structure near the Fermi level, which, in combination with inversion symmetry breaking, ferromagnetism, and strong spin-orbit coupling contributed by heavy Te element, creates a possible bulk spin-valley locked electronic state with valley polarization as suggested by our DFT calculations. Further, this material can also be easily exfoliated to 2D atomically thin layers. Therefore, this material offers a unique platform to explore the physics of valleytronic states with spontaneous spin and valley polarization in both bulk and 2D atomic crystals.

Doped TiO2slabs for water splitting: a DFT study

AbstractThe realization of water splitting at a commercial scale is one of the major obstacles to the development of a viable and long-term hydrogen economy. In this regard 3d-transition metals (TMs) doped anatase TiO2slabs are investigated to understand the role of magnetism in water splitting using density functional theory (DFT). The structural stability of various 3d-TMs (V, Cr, Mn, Fe, Co, Ni, and Cu) doped in TiO2ultrathin films have been investigated. The electronic band structures show that the doping of 3d-TMs makes the bandgap of TiO2narrow which leads to the improvement of photo-reactivity as well as maintains the strong redox potential. The large magnetic moment of Fe- and Mn-doped slabs indicates that high charge transfer to water molecules with low adsorption energy. The results demonstrate that V, Fe, and Co doping makes the slabs ferromagnetic (FM), whereas Cr, Mn, Ni, and Cu doping makes the slabs non-magnetic. The water molecule is placed on each FM slab and their splitting behavior has been analyzed thoroughly. It was concluded that magnetism does not affect water splitting.

Modeling and Simulation of Magnons Scattering Across Shear Spins in Multilayered Ferromagnetic Slabs

In this work, we introduce a computer model and theoretical approach based on the matching technique to investigate the spin precession and the magnetic properties of an ordered magnetic interface joining two ferromagnetic multilayers of type AB, made of 10 spin slabs, obtained by alternative two spin layers A and B. We simulate, particularly, the coherent magnon transmission through spins’ interface, in multilayered thin films, obtained by shearing a part of the film from the other at an angle of 30∘. The individual and total transmittance of bulk magnons of the thin film, scattering coherently at the shearing interface zone and the localized magnonic spin states, are calculated and analyzed. The transmission and reflection spin modes are derived as elements of a Landauer–Büttiker type scattering matrix. The results highlight the localized spin states on the interface shear domain and their interactions with incident magnons. The evolutions of the magnonic spectra can be presented for arbitrary directions of the incident magnons on the boundary zone, for all accessible frequencies in the propagating bands as well as for the magnetic exchange coupling between each spin A(B) and its adjacent sites and their spin intensity. The results demonstrate the dependence of the magnonic spectra for the perfect multilayered films and at the inhomogeneous domain of the interface shear. The analysis of the spectra illustrates the fluctuations, related to Fano resonances, due to the coupling between travelling magnons and the localized modes in the shear interface domain. The calculated spectra could yield useful information concerning the magnetic parameters of such interface slabs in multilayered films.

Giant demagnetization effects induced by superconducting films

We show that a ferromagnetic (F) slab with the in-plane magnetization sandwiched between two superconducting (S) films experiences strong demagnetization effect due to the Meissner screening of the stray magnetic field by superconductors. In the extreme case, the transition of the S film from normal to the superconducting state can switch the demagnetization factor from 0 to 1, which is in a sharp contrast with the S/F bilayers where such transition affects the magnetic field inside the F film only slightly. The giant demagnetization effect is shown to be qualitatively robust against the decreasing superconducting film thickness and may provide a hint toward the explanation of the anomalously large ferromagnetic resonance frequency shift recently observed for the S/F/S structures [Golovchanskiy et al., Phys. Rev. Appl. 14, 024086 (2020)].

Polarized waveguide excitations in microwave ferrites: The singularity structure analysis

In this work, we delve into the structure of some typical microwave ferrites while investigating the propagation of nonlinear circularly polarized waveguide excitations. In the standpoint, we consider a ferromagnetic slab insulator of 0.5 mm thickness submitted to an external transverse magnetic field. Combining the Landau–Lifshitz-Gilbert formalism of evolution of the magnetization to Maxwell equations, we survey the interaction process of an electromagnetic wave perturbation with the slab. As a result, using the perturbative scaling approach suitable to high-frequency excitations, we derive some new evolution system describing the propagation of circularly polarized waves in the medium. Pursuing further with the analysis, we unwrap the integrability properties of the new system using the singularity structure method where sufficient arbitrary functions are generated. Taking advantage of such properties, we construct a rich variety of nonlinear excitations, solutions to the ferrite dynamics. Additionally, we address some physical implications of the results obtained previously.

Twist-Induced Near-Field Thermal Switch Using Nonreciprocal Surface Magnon-Polaritons

We explore that two ferromagnetic insulator slabs host a strong twist-induced near-field radiative heat transfer in the presence of twisted magnetic fields. Using the formalism of fluctuational electrodynamics, we find the existence of large twist-induced thermal switch ratio in large damping condition and nonmonotonic twist manipulation for heat transfer in small damping condition, associated with the different twist-induced effects of nonreciprocal elliptic surface magnon-polaritons, hyperbolic surface magnon-polaritons, and twist-non-resonant surface magnon-polaritons. Moreover, the near-field radiative heat transfer can be significantly enhanced by the twist-non-resonant surface magnon-polaritons in the ultra-small damping condition. Such twist-induced effect is applicable for other kinds of anisotropic slabs with timereversal symmetry breaking. Our findings provide a way to twisted and magnetic control in nanoscale thermal management and improve it with twistronics concepts.

Measurement of Ferromagnetic Slabs Permeability Based on a Novel Planar Triple-Coil Sensor

Eddy current methods are wildly used for measuringthe electromagnetic property of ferromagneticsamples due to its high sensitivities and portability (when using the remote electromagnetic sensor). However, in diverse applications, the eddy current measurement is always hampered by the lift-off variation – the gap between the sensing probe and the sample. In this paper, the measurement error of the permeability caused by the lift-off variation could be significantly reduced when using a developed planar triple-coil sensor. An inverse algorithm, the single-frequency eddy current algorithm is established for the evaluation of the permeability by referring to the phase of themeasured impedance or inductance. Based on the experiments of several ferromagnetic samples when using the developed sensor and inverse algorithm, the measured permeability is proved can be almost immune to the lift-off variations.

Reply to “Comment on ‘Optical detection of transverse spin-Seebeck effect in permalloy film using Sagnac interferometer microscopy’ ”

In their Comment, Kimling and Kuschel (hereafter the commenters) challenge our original interpretation of the magneto-optical Kerr effect (MOKE) measurements using ultrasensitive Sagnac interferometer, claiming that the transverse spin-Seebeck effect (TSSE) is not the only contribution to the measured change in the Kerr rotation angle from a Ni80Fe20 (NiFe) ferromagnetic (FM) slab subjected to a lateral temperature gradient in the presence of a magnetic field. The authors assert that: (1) the TSSE, in general, has not been completely proven so far, and that the existing theories, in particular the phonon magnon drag model that we have used in our publication, in fact cannot explain the original work of Uchida et al. (2) The commenters based their critique on an estimate of the magnitude of the measured effect, arguing that to observe the TSSE that we originally claimed, the temperature gradient in our measurements should have been much larger than the value we measured. In this Reply, firstly, we summarize previous literature reports on the TSSE response in FM metallic systems. Secondly, we dispute the estimate of the necessary large temperature gradient made by the commenters. Importantly, the Kerr effect sensitivity to spin accumulation (via the TSSE response) has not been recognized by the commenters, in fact it was mistakenly assumed that the Kerr effect sensitivity to the spin accumulation by the TSSE is the same as the Kerr sensitivity to the bulk magnetization change due to the temperature change. In conclusion, we show that the TSSE is the only viable interpretation of our original measurements, and that the phonon-magnon drag model is indeed capable of explaining our results.

Shape Magnetic Anisotropy From Spin Density in Nanoscale Slab Systems

We developed a computational method for estimating magnetic dipole energy of slab materials using spin density obtained through a density functional approach. The new method can accurately estimate magnetic anisotropy energy (MAE) for slabs from magnetic dipole interaction called shape MAE (SMAE). We investigated ferromagnetic and antiferromagnetic slabs and found that a quadrupole component of atomic spin density suppresses SMAE in ferromagnetic slabs with Fe/MgO interface. In antiferromagnetic MnPt slabs, which have a perpendicular favor originating from the crystalline magnetic dipole interaction, a surface effect at the Mn edge appears as an enhancement of SMAE.

Polarization of Electromagnetic and Spin Waves in Metallic Slab

We have considered theoretically the eigenmodes as well as forced electromagnetic and spin waves in ferromagnetic metallic slabs for different boundary conditions for magnetization. We present an algorithm for determination of microwave fields and dynamic magnetization within the slab as well as the transmitted and reflected microwave fields outside the slab. We determine the polarization of the studied waves and show that spatial oscillations of the polarization are formed within the slab. The found oscillations are in particular profound close to the surfaces of the slab in the case of strong surface pinning of spins.

Phase Diagrams of a Ferrimagnetic Superlattice in a Transverse Field: a Quantum Monte Carlo Simulation

In this work, quantum Monte Carlo simulation based on the Trotter-Suzuki formalism has been used to study the phase diagrams of a superlattice formed by two ferromagnetic slabs A and B with an antiferromagnetic interfacial coupling in a Transverse field. The effect of the transverse field Ω, the exchange coupling J A , and the thickness of the two slabs A and B on the phase diagrams of the system have been investigated. A number of interesting phenomena have been found. In particular, the superlattice can exhibit a compensation temperature T k or a compensation transverse field Ω k for certain ranges of the exchange interactions. The dependence of the critical and compensation behaviors on the slabs thicknesses has been also discussed.

AC induction heating of ferromagnetic slabs saturated with a DC field

PurposeThis study aims to investigate the feasibility of saturated AC heating of magnetic metals. In AC heating of magnetic steel below the Curie temperature, because of the high magnetic permeability, the penetration depth is in the order of 1-6 mm at 50 Hz. Surface heating is then obtained, in practice, if large slabs are processed. The necessity to provide the required surface-to-core temperature uniformity (about 25°C) at the end of the heating process, avoiding excessive thermal stresses which can lead to cracks, thus implies a long heating time.Design/methodology/approachThe penetration depth can be increased if the material is brought to saturation by applying an external DC magnetic field, and a faster in-depth heating can be obtained. The DC saturating field can be produced with no losses over large volumes by means of superconducting (SC) coils.FindingsThe feasibility of in-depth induction heating of a 200 × 1,000 × 5,000 mm magnetic steel slab with an applied 2 T DC saturating field is numerically investigated. The results show that the use of a DC saturating field leads to shorter processes which fulfil the heating objectives.Practical implicationsA DC saturating field cannot be produced by means of copper coils because of the large amount of material and the unaffordable power required. However, this field can effectively be produced by means of SC magnets based on state-of-the-art materials.Originality/valueSuperconductivity may be the enabling technology for fast and efficient induction heating of magnetic steel slabs if the increase in productivity can balance the additional costs due to the SC magnet.

Magnetocrystalline anisotropy of Fe and Co slabs and clusters onSrTiO3by first-principles

In this work, we present a detailed theoretical investigation of the electronic and magnetic properties of ferromagnetic slabs and clusters deposited on SrTiO$\_3$ via first-principles, with a particular emphasis on the magneto-crystalline anisotropy (MCA). We found that in the case of Fe films deposited on SrTiO$\_3$ the effect of the interface is to quench the MCA whereas for Cobalt we observe a change of sign of the MCA from in-plane to out-of-plane as compared to the free surface. We also find a strong enhancement of MCA for small clusters upon deposition on a SrTiO$\_3$ substrate. The hybridization between the substrate and the $d$-orbitals of the cluster extending in-plane for Fe and out-of-plane for Co is at the origin of this enhancement of MCA. As a consequence, we predict that the Fe nanocrystals (even rather small) should be magnetically stable and are thus good potential candidates for magnetic storage devices.

Theoretical and Experimental Analysis of an Induction Planar Actuator with Different Secondaries--A Planar Driver Application for Metallic Surface Inspection.

This paper presents a study on an induction planar actuator concept. The device uses the same principles as a linear induction motor in which the interaction between a travelling magnetic field and a conducting surface produces eddy currents that leads to the generation of a thrust force and can result in movement over a metallic surface. This can benefit the inspection of metallic surfaces based on the driving platform provided by the induction planar actuator. Equations of the magnetic and electric fields are presented and, by means of these equations, the forces involved were calculated. The behaviour of thrust and normal forces was analysed through the equations and by numerical models, and compared with the results obtained by measurements on a device prototype built in the laboratory as part of the study. With relation to the surface under inspection that forms the secondary, three cases were analysed: (1) a double-layered secondary formed by aluminium and ferromagnetic slabs; (2) a single aluminium layer and (3) a single ferromagnetic layer. Theoretical and measured values of thrust and normal forces showed good correlation.

A magnetostatic force inspection method for monitoring the oscillation marks of continuous casting

Based on the well-known fact that ferromagnetic materials can be significantly attracted by a permanent magnet (PM), we develop an innovative magnetostatic force inspection method to monitor the oscillating marks formed during continuous casting. A small PM produces a static magnetic field that penetrates into the ferromagnetic material slab formed via continuous casting. This magnet forms a localized magnetic sensing zone (MSZ) within the ferromagnetic material. The magnetostatic force acting on the ferromagnetic material can be expressed as the Maxwell tensor integral over the surface of the ferromagnetic material within the MSZ. This force provides local surface profile information. The reaction force of the magnetostatic force acting on the PM can be measured using a laser–cantilever system (a high force resolution method), and thus the profile features of the oscillation marks can be obtained. A measuring device with a laser–cantilever system is designed, constructed, and applied in a series of prototypes and a static experiment. A numerical model is simultaneously constructed to validate the measurement results. The differences between the actual and measured profiles are analyzed. An actual steel specimen with oscillation marks is measured using this device, and the accuracy is evaluated. In summary, the potential for the application of this method in the metallurgy industry is demonstrated.

Substrate integrated waveguide isolator based on ferromagnetic nanowires in porous alumina template

We demonstrate the operation of a fully integrated and miniaturized waveguide based on ferromagnetic nanowires as a promising alternative to macroscopic ferrite slab-loaded metallic rectangular waveguides used as microwave isolators. Nanowires of various heights are selectively grown at dedicated areas into a low-loss nanoporous alumina template in order to create the shielding walls of a Substrate Integrated Waveguide (SIW) topology and the ferromagnetic slab supporting a circularly polarized nonreciprocal propagation. A model is proposed for the microwave response of the SIW and its non-reciprocity, which takes into account the substrate permittivity and the tensorial permeability of the ferromagnetic nanowires, and its predictions are validated by measurements. A significant isolation of 7 dB/cm is obtained experimentally at 13.5 GHz, without the need of a DC bias magnetic field.

Ferroelectric-ferromagnetic multilayers: A magnetoelectric heterostructure with high output charge signal

Multiferroic composites and heterostructures comprising ferroelectric and ferromagnetic materials exhibit room-temperature magnetoelectric (ME) effects greatly exceeding those of single-phase magnetoelectrics known to date. Since these effects are mediated by the interfacial coupling between ferroic constituents, the ME responses may be enhanced by increasing the density of interfaces and improving their quality. A promising material system providing these features is a ferroelectric-ferromagnetic multilayer with epitaxial interfaces. In this paper, we describe theoretically the strain-mediated direct ME effect exhibited by free-standing multilayers composed of single-crystalline ferroelectric nanolayers interleaved by conducting ferromagnetic slabs. Using a nonlinear thermodynamic approach allowing for specific mechanical boundary conditions of the problem, we first calculate the polarization states and dielectric properties of ferroelectric nanolayers in dependence on the lattice mismatch between ferroic constituents and their volume fractions. In these calculations, the ferromagnetic component is described by a model which combines linear elastic behavior with magnetic-field-dependent lattice parameters. Then the quasistatic ME polarization and voltage coefficients are evaluated using the theoretical strain sensitivity of ferroelectric polarization and measured effective piezomagnetic coefficients of ferromagnets. For Pb(Zr0.5Ti0.5)O3−FeGaB and BaTiO3−FeGaB multilayers, the ME coefficients are calculated numerically as a function of the FeGaB volume fraction and used to evaluate the output charge and voltage signals. It is shown that the multilayer geometry of a ferroelectric-ferromagnetic nanocomposite opens the way for a drastic enhancement of the output charge signal. This feature makes biferroic multilayers advantageous for the development of ultrasensitive magnetic-field sensors for technical and biomedical applications.

Investigation of effects of inhomogeneous exchange within ferrites

In this paper, we investigate the effects of inhomogeneous exchange on the magnetization dynamics within a ferromagnetic slab of 0.5mm thickness from the viewpoint of the Landau–Lifshitz–Gilbert phenomenological theory of damping in ferromagnets. As a result, we unearth a new coupled system of magnetization dynamics in which structural analysis reveals the existence of soliton propagation in the above ferrite.