Isotropic Magnetic Properties Research Articles

Magnetic field sensing elements based on Ni80Fe20 2D magnetoplasmonic crystals

Here we demonstrate the fabrication of magnetic field sensing elements based on 2D magnetoplasmonic crystals prepared using e-beam lithography and magnetron sputtering methods. The magnetoplasmonic crystals consist of square lattice diffraction gratings with varying filling factors layered with Ag, Ni80Fe20, and Si3N4 layers. Based on the magnetic, optical, and magneto-optical studies, the magnetoplasmonic crystal that allows for both high transverse Kerr effect and isotropic in-plane magnetic properties along the diffraction grating vectors was determined. The sensitivity and measuring range of this sample provide a perspective for measuring several components of an external magnetic field.

The influence of antiferromagnetic spin cantings on the magnetic helix pitch in cubic helimagnets

In cubic helimagnets MnSi and Cu2OSeO3 with their nearly isotropic magnetic properties, the magnetic structure undergoes helical deformation, which is almost completely determined by the helicoid wavenumber k=D/J , where magnetization field stiffness J is associated with isotropic spin exchange, and D is a pseudoscalar value characterizing the antisymmetric Dzyaloshinskii–Moriya (DM) interaction. Another magnetic feature of these crystals, also caused by the DM interactions, are antiferromagnetic spin cantings, similar to the ferromagnetic cantings responsible for the phenomenon of weak ferromagnetism. Here we show that cantings can strongly influence the helical order through the value of the parameter D . Changing the cantings in a strong magnetic field is predicted to affect the magnon spectrum of the crystals.

Surface Morphology and Exchange Bias Anisotropy Studies in Large Area Deposited Co2FeSi Ir50Mn50 Multi Layers For Spintronic Applications

Surface morphology and magnetic properties of ferromagnetic Heusler alloy Co2FeSi thin films and their multi-layers with anti-ferromagnetic Ir50Mn50, which find applications in spintronic devices were investigated. The sputtering process flow for large area deposition of thin films on 3 inch size thermally oxidized single crystal Si(100)/SiO2 substrates have been developed by optimizing the sputtering geometry and other process parameters. A uniform film composition, thickness, smooth surface, good crystallinity and magnetic properties have been achieved in the films over 3-inch size wafers. The isotropic magnetic properties such as saturation/remanent magnetizations, coercivity were achieved in Co2FeSi films deposited on 3-inch size Si(100)/SiO2 wafers with 15 nm Cr buffer layer. An exchange bias anisotropy has been established in Co2FeSi/IrMn multilayer by magnetic annealing process using in-house made magnetic annealing set up. A maximum exchange bias anisotropy field, Hex of 178 Oe and low coercivity, Hc of 85 Oe has been achieved in the Co2FeSi/IrMn multilayer stacks suitable for magnetic tunnel junctions for spintronic applications.

Selective laser sintering of bonded anisotropic permanent magnets using an in situ alignment fixture

PurposeAdditive manufacturing (AM) techniques have been developed to rapidly produce custom designs from a multitude of materials. Bonded permanent magnets (PMs) have been produced via several AM techniques to allow for rapid manufacture of complex geometries. These magnets, however, tend to suffer from lower residual induction than the industry standard of injection moulding primarily due to the lower packing density of the magnetic particles and secondly due to the feedstock consisting of neodymium-iron-boron (Nd-Fe-B) powder with isotropic magnetic properties. As there is no compaction during most AM processes, increasing the packing density is very difficult and therefore the purpose of this study was to increase the magnetic properties of the PMs without increasing the part density.Design/methodology/approachAccordingly, this research investigates the use of anisotropic NdFeB feedstock coupled with an in-situ alignment fixture into an AM process known as selective laser sintering (SLS) to increase the magnetic properties of AM magnets. A Helmholtz coil array was added to an SLS machine and used to expose each powder layer during part fabrication to a near-uniform magnetic field of 20.4 mT prior to consolidation by the laser.FindingsPermeagraph measurements of the parts showed that the alignment field introduced residual induction anisotropy of up to 46.4 ± 2.2% when measured in directions parallel and perpendicular to the alignment field. X-ray diffraction measurements also demonstrated a convergence of the orientation of the crystals when the magnets were processed in the presence of the alignment field.Originality/valueA novel active alignment fixture for SLS was introduced and was experimentally shown to induce anisotropy in bonded PMs. Thus demonstrating a new method for the enhancement in energy density of PMs produced via AM methods.

Magnetic properties and microstructure of Sm-Co-Fe-Cu-Zr-Hf spark plasma sintered magnets

In this work, Sm24.6Co50Fe17·4Cu5·7Zr2.3-xHfx (x = 0–2.0) ribbons and magnets were prepared by melt-spinning method and spark plasma sintering (SPS) technique. The magnetic properties of the melt-spun ribbons with Hf addition are much higher than those of the Hf-free ribbons in the temperature range of 300–400 K. The optimal comprehensive magnetic properties of ribbons and isotropic magnets were obtained with 1.0 wt% Hf substitution. Microstructural results showed that Hf elements do not enter into the hard magnetic 1:7H and 2:17R phase in SPSed magnets and Zr–Hf rich phases are formed around grain boundaries as particulates. The enhancement of magnetic properties of the ribbons and SPSed magnets can be attributed to grain refinement and more uniform microstructure as a result of Hf addition. The micro-twin structure of 2:17R phase also have been discovered in the spark plasma sintered magnets. This work may provide a rapid preparation of Sm2Co17 magnets.

Regulating microwave absorption and energy bandgap using cauliflower-like polyaniline coated on La0.8Sr0.2FeO3 nanoparticles

In this research, La0.8Sr0.2FeO3/cauliflower-like polyaniline (PANi) nanocomposite was architected based on a novel complementary method using dodecylbenzenesulfonic acid as a doping agent. The prepared nanocomposite was characterized using Fourier transform infrared, X-ray powder diffraction, field emission scanning electron microscopy, vibrating sample magnetometer diffuse reflection spectroscopy, and vector network analyzer analyses. All of the used analyses attested that the pure structure of materials has been synthesized. Polarizability, energy bandgap, magnetic property, and microwave absorbing features were tailored by loading the various mass fraction of PANi. Exclusive interactions between the nanoparticles with alkaline property and aniline monomers along the experimental route led to the preparation of nanocomposite with unique morphology. Inserting PANi augmented softness and isotropic magnetic property of the prepared nanocomposite, desirable for microwave absorption. Moreover, polyacrylonitrile (PAN) was applied as a novel microwave absorbing matrix. The maximum reflection loss (RL) of La0.8Sr0.2FeO3/PANi10%/PAN was − 69.24 dB at 12.62 GHz with an efficient bandwidth of 6.47 GHz (RL < − 10 dB) meanwhile the efficient bandwidth was enhanced to 6.97 GHz (RL < − 10 dB) for La0.8Sr0.2FeO3/PANi30%/PAN nanocomposite.

Influence of iron powder core on the switched reluctance motor performance enhancement

Soft Magnetic Composite (SMC) materials possess isotropic magnetic and thermal properties, very low eddy current loss and relatively low total core loss at medium and higher frequencies. This paper presents the application potential of iron powder SMC in switched reluctance machine (SRM) and its performance enhancement. The results of extensive finite element simulation and experimental validation of the proposed fabricated prototype are delineated. The study concludes that the use of SMC as magnetic core of a switched reluctance motor enhances its thermal and vibration characteristics in comparison with the conventional lamination counterpart.

Effect of Sb substitution on crystal structure, texture and hard magnetic properties of melt-spun MnBi alloys

Melt-spun Mn50Bi50-xSbx alloys with x ≤ 5 were prepared at different solidification rates and characterized both in the as-spun state and after annealing. In the as-spun alloys, the Sb substitution leads to the formation of a metastable phase, similar to the binary “quenched high-temperature phase” but without the superstructure of the latter and exhibiting a different – increasing – temperature dependence of coercivity. The new nanocrystalline metastable phase is not only itself characterized by a high room-temperature coercivity (in excess of 20 kOe), but upon annealing it transforms into a high-coercivity (up to 13.5 kOe) “low-temperature” α phase. However, the advantage of obtaining a high coercivity without the otherwise required milling made possible by the Sb substitution is undermined by the absence of a local crystallographic texture in the melt-spun alloys. The best combination of the isotropic hard magnetic properties realized for the Mn55Bi43.5Sb1.5 composition is a remanence of 35.5 emu/g and a coercivity of 8.1 kOe. The annealed Sb-free Mn50Bi50 alloys did possess a local crystallographic alignment and, for high solidification rates, a moderate coercivity up to 5.6 kOe; however, they had an inadequate “rectangularity” in the demagnetization curve. The orthorhombic compound known as MnBi0.9Sb0.1 and described earlier as antiferromagnetic was obtained in the annealed ribbons with x ≈ 5. The compound was found to order ferromagnetically between 200 K and ≈250 K and to exhibit a significant coercivity, 14.3 kOe at 50 K. It is suggested that the MnBi0.9Sb0.1 may actually be a Sb-stabilized “new phase” observed earlier as metastable in the Bi–MnBi eutectic alloys.

Evaluating the Suitability of Partial Recrystallization as a Strengthening Method for Thin-Gauge, High-Strength Non-Orientated Electrical Steel

The increasing need for electric/hybrid electric vehicles to compete with fossil fuel-powered cars has led to new requirements and designs of the electric motor. Non-grain oriented steel (NOES) is primarily used within the electric motor to form both stator and rotor sections (dependent on design) and has traditionally been developed to possess excellent isotropic magnetic properties with little or no consideration for strength. The drive toward more powerful or efficient electric motors has resulted in higher rotational speeds and increasing associated requirements for high-strength NOES. This paper looks at utilizing the well-known theory of partial recrystallization as a strengthening mechanism to determine if the strengthening effects and associated magnetic properties are acceptable for use within the rotor section. It was found that partial recrystallization can be utilized to tailor the microstructure of NOES to create higher strength NOES that withstands operating conditions and compares favorably to commercially available high-strength NOES grades, making it a viable option.

Influence of crystal orientation on the magnetostriction behavior of Fe films formed on MgO single-crystal substrates

Abstract Fe thin films are prepared on MgO substrates of (001), (110), and (111) orientations by ultra-high vacuum magnetron sputtering. The magnetostriction behaviors under rotating magnetic fields are observed by using a cantilever method. The relationship between in-plane magnetic anisotropy and magnetostriction behavior is investigated. An Fe(001)bcc single-crystal film is obtained on MgO(001) substrate. A four-fold symmetry in in-plane magnetic anisotropy is observed for the Fe(001)bcc film, where the easy magnetization directions are parallel to bcc[100] and bcc[010]. An Fe(211)bcc bi-crystalline film is formed on MgO(110) substrate and the film also shows an almost four-fold symmetric magnetic anisotropy. The reason is interpreted to be due to an influence of overlap of magnetic anisotropies of two bcc(211) variants with two effective easy magnetization directions which are obtained by projecting bcc[010] and bcc[001] on the bcc(211) plane. An Fe(110)bcc film is epitaxially grown on MgO(111) substrate with two types of variant with the crystallographic orientation relationships similar to Nishiyama-Wasserman and Kurdjumov-Sachs. The Fe(110) film shows an isotropic in-plane magnetic property due to an influence of the variant structure. Usual sinusoidal waveforms of magnetostriction are observed for the Fe(110) film. On the other hand, waveforms measured for the Fe(001) and the Fe(211) films are deformed from sinusoidal shape under low in-plane rotating magnetic fields and the magnetostriction behaviors are similar between the two films. Rectangular waveforms are observed for the bending parallel to easy magnetization directions, whereas triangular waveforms are recognized for the bending parallel to hard directions. The phenomenon is related to the direction difference between applied magnetic field and magnetization in magnetically unsaturated films with in-plane anisotropies. The magnetostriction behavior is influenced by the symmetry of in-plane magnetic anisotropy.

Preparation of neat and capped BaFe2O4 nanoparticles and investigation of morphology, magnetic, and polarization effects on its microwave and optical performance

In this study, pure BaFe2O4 nanoparticles were prepared using the citrate gel method and then the presence of glucose as a novel organic capping agent on its characteristics was explored. Moreover, neat BaFe2O4 nanostructures were synthesized at 650 °C or 850 °C, which results confirmed the heat treatments have a significant effect on its properties. Besides, microwave absorbing mediums were compared by silicone rubber or Polyvinylidene fluoride (PVDF) polymeric matrices. The Fourier transform infrared (FT-IR) revealed that BaFe2O4 structures at 650 °C or 850 °C, as well as capped nanoparticles at 850 °C were formed without any organic impurities. The results of the vibrating sample magnetometer (VSM) exhibited that the heat treatment at 850 °C led to an increase in the saturation magnetization (Ms) as well as on one hand organic capping agent diminished Ms, on the other hand, enhanced the isotropic magnetic property of the nanoparticles. X-ray powder diffraction (XRD) patterns illustrated pure crystal structure for all three samples with a size of 10.2 nm calculated by the Scherrer equation. Additionally, field emission scanning electron microscopy (FE-SEM) and diffuse reflection spectroscopy (DRS) analysis illustrated that the calcination temperature and organic capping agent respectively changed morphology and band gap of synthesized nanostructures. Finally, Microwave absorption properties were studied using vector network analyzer (VNA). Based on the results, the maximum reflection loss of capped BaFe2O4 at 850 °C/silicone rubber nanocomposite was −82.74 dB at 11.2 GHz with a thickness of 2.5 mm also BaFe2O4 at 650 °C/silicone rubber nanocomposite absorbed 7.39 GHz bandwidth more than 10 dB with a thickness of 2 mm in the x and ku-band frequency.

Fe-Al alloy single-crystal thin film preparation for basic magnetic measurements

Fe100–xAlx (x = 0, 4, 10, 20, 30 at. %) alloy films of 40 nm thickness are prepared on MgO(001) single-crystal substrates by varying substrate temperature from room temperature to 600 °C. Single-crystal films of (001) orientation with bcc-based disordered A2 structure are obtained for the Al content range of x = 0 - 20 at. %. An ordered phase of DO3 structure is observed in Fe70Al30 films prepared at temperatures higher than 200 °C, whereas (001) oriented single-crystal films of A2 structure are obtained when prepared at room temperature. The film surface profile does not depend much on the film composition, while the surface roughness increases with increasing substrate temperature. Island-like crystals are observed for films prepared at 600°C for all compositions. Difference in lattice spacing measured parallel and perpendicular to the substrate is noted for the single-crystal thin films and it increases with increasing Al content. The lattice strain in single-crystal film is caused possibly to accommodate the lattice mismatch with the MgO substrate. The (001)-oriented single-crystal films with A2 structure show four-fold symmetries in in-plane magnetic anisotropy with the easy magnetization axis A2[100] and the hard magnetization axis A2[110], whereas the films with DO3 ordered structure show almost isotropic magnetic properties.

Anisotropic magnetic property of nanocomposite Nd2Fe14B/Mo/α-Fe multilayer films

We fabricated the MgO(100)/Mo/[Nd2Fe14B/Mo/Fe/Mo]5/Mo multilayer films, in which we tried to avoid the negative Jex interfaces and thermal diffusion between Nd2Fe14B and α–Fe layers by forming the stacked structure with ultra thin Mo interlayer. The films without Mo interlayer showed isotropic magnetic properties, while films with Mo interlayer thickness tMo = 1 nm exhibited the perpendicular anisotropy with the coercivity of 7 kOe. Shapes for the major loop and the first order reversal curves (FORCs) suggested an existence of positive exchange coupling between the Nd-Fe-B and the α–Fe layers via the 1 nm thick Mo interlayer.

Magnetization reversal processes of isotropic permanent magnets with various inter-grain exchange interactions

We performed a large-scale micromagnetics simulation on a supercomputing system to investigate the properties of isotropic nanocrystalline permanent magnets consisting of cubic grains. In the simulation, we solved the Landau–Lifshitz–Gilbert equation under a periodic boundary condition for accurate calculation of the magnetization dynamics inside the nanocrystalline isotropic magnet. We reduced the inter-grain exchange interaction perpendicular and parallel to the external field independently. Propagation of the magnetization reversal process is inhibited by reducing the inter-grain exchange interaction perpendicular to the external field, and the coercivity is enhanced by this restraint. In contrast, when we reduce the inter-grain exchange interaction parallel to the external field, the coercivity decreases because the magnetization reversal process propagates owing to dipole interaction. These behaviors show that the coercivity of an isotropic permanent magnet depends on the direction of the inter-grain exchange interaction.

Columnar structured FePt films epitaxially grown on large lattice mismatched intermediate layer.

The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) <100>//ZrN (001) <100>//TiN (001) <100> among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO2-C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO2-C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained.

Development of Magnetostrictive Resonant Torsional Vibrator

In this paper, the design, construction, and operation of a magnetostrictive resonant torsional vibrator are described. To generate torsional vibration, two magnetostrictive patches are bonded on an aluminum horn. Two magnetic fields, longitudinal and circumferential, are applied into the patches. As a result, the magnetostrictive patches vibrate torsionally based on the Wiedemann effect. The magnetostrictive patches are made of 2V permendur, which has isotropic magnetic properties. The principle of the torsional vibrator is explained, and differential equations of torsional vibration of the horn are derived. A torsional horn is designed for a resonant frequency of 8515 Hz. The experimental results show that the torsional angle of the tip of the horn is $5.44\times 10^{-6}$ rad. This type of vibrator is exploited in applications that require torsional vibration, such as miniature ultrasonic motors or ultrasonicassisted bone drilling system. In other words, the vibrator is used as an actuator.

Magnetoelectric polymer nanocomposite for flexible electronics

This paper reports the fabrication and characterization of a new type of magnetoelectric polymer nanocomposite that exhibits excellent ferromagnetism and ferroelectricity simultaneously at room temperature. The multiferroic nanocomposite consists of high aspect ratio ferromagnetic iron nanowires embedded inside a ferroelectric co-polymer poly(vinylindene fluoride-trifluoroethylene), P(VDF-TrFE). The nanocomposite has been fabricated via a simple low temperature spin coating technique. Structural, ferromagnetic, ferroelectric, and magnetoelectric properties of the developed nanocomposite have been characterized. The nanocomposite films showed isotropic magnetic properties due to the random orientation of the iron nanowires inside the film. In addition, the embedded nanowires did not hinder the ferroelectric phase development of the nanocomposite. The developed nanocomposite showed a high magnetoelectric coupling response of 156 mV/cmOe measured at 3.1 kOe DC bias field. This value is among the highest reported magnetoelectric coupling in two phase particulate polymer nanocomposites.

Nanocrystalline magnetite thin films grown by dual ion-beam sputtering

We have explored the influence of an ion-assisted beam in the thermoelectric and magnetic properties of nanocrystalline magnetite thin films grown by ion-beam sputtering. The microstructure has been investigated by XRD. Tensile and compressive strained thin films have been obtained as a function of the parameters of the ion-assisted beam. The evolution of the in-plane magnetic anisotropy was attributed to crystalline grain size. In some films, magneto-optical Kerr effect measurements reveal the existence of uniaxial magnetic anisotropy induced by the deposition process related with a small grain size (⩽20nm). Isotropic magnetic properties have observed in nanocrystalline magnetite thin film having larger grain sizes. The largest power factor of all the films prepared (0.47μW/K2cm), obtained from a Seebeck coefficient of −80μV/K and an electrical resistivity of 13mΩcm, is obtained in a nanocrystalline magnetite thin film with an expanded out-of-plane lattice and with a grain size ≈30nm.

Local Magnetic Properties in Non-oriented Electrical Steel and Their Dependence on Magnetic Easy Axis and Misorientation Parameters

Abstract An understanding of how material parameters, especially orientation and misorientation, influence the magnetic properties of non-oriented electrical steel (NOES) is important for improving the efficiency of the material in service. In this study, the local magnetic properties were measured using magnetic Barkhausen noise (MBN) on different test locations on different strips of NOES material. Local variations in magnetic properties, texture, and misorientation were revealed. A new interpretation for misorientation, called the easy axis misorientation (EAM), was created to describe the alignment of the magnetic easy axes between neighboring grains. This new EAM, visualized as a single value parameter or graphed as a distribution, was shown to be more effective at predicting the isotropic magnetic properties than previously used texture parameters based on standard orientation/misorientation definitions. It was found that a larger EAM value, especially when associated with a lower small angle EAM intensity distribution, was associated with a larger MBN energy. A larger MBN energy has been previously associated with lower losses, and therefore a greater material efficiency.

Effects of film composition and substrate orientation on the structure and the magnetic properties of Fe-Co-B alloy films formed on MgO single-crystal substrates

(Fe0.7Co0.3)100−x B x alloy thin films are prepared on MgO single-crystal substrates with (100), (110), and (111) orientations at 200C by ultra-high vacuum radio-frequency magnetron sputtering with various B compositions, x, from 0 to 15 at.%. The effects of composition and substrate orientation on the structure and the magnetic properties are studied. Fe-Co epitaxial films with bcc structures are obtained on all substrates. Fe-Co(100) single-crystal films are formed on MgO(100) substrates. Fe-Co films epitaxially grown on MgO(110) substrates consist of two (211) variants whose orientations are rotated around the film’s normal by 180 each other. Fe-Co(110) films grow epitaxially on MgO(111) substrates with two types of variants, Nishiyama-Wasserman and Kurdjumov-Sachs relationships. As the B composition increases up to around 5 at.%, the film involves an amorphous structure in addition to an epitaxial bcc crystal structure. With further increases in the B content, the film is only amorphous. The magnetization properties of the films involving epitaxial crystals reflect the magnetocrystalline anisotropy of the bulk Fe-Co crystal. The easy magnetization direction varies depending on the crystallographic orientation of the film. Isotropic in-plane magnetic properties are observed for amorphous films.