Changes In Magnetic Domain Structure Research Articles

Real-Time Observation of Magnetic Domain Structure Changes with Increasing Temperature for Z-Type Hexagonal Ferrite.

Z-type hexagonal ferrites have recently received attention for their room-temperature magnetoelectric (ME), which is activated when the temperature at which the transverse-conical spin-state transitions to a ferrimagnetic state is increased. The changes in the magnetic domain structure at the transition have been well-documented; however, they are still not understood in detail. In the present study, Lorentz transmission electron microscopy (TEM) analysis combined with an in situ heating experiment was conducted to demonstrate the shift in magnetic domain structure during the transition from the transverse-conical spin arrangement to a ferrimagnetic spin order. The dynamics of the magnetic domain structure changes with the increasing temperature were acquired in real-time. At 490 K, the magnetization transition from the transverse-conical spin state to the ferromagnetic state was demonstrated. Cross-tie domain walls formed during the magnetic transition process. The increased effect of the demagnetizing field applied to the 180° magnetic domains was caused by a lower magnetocrystalline anisotropy (MCA) at the easy axis of magnetization.

Perpendicular magnetization anisotropy induced dynamical coherence reduction in stripe domain film

We investigated the magnetization dynamics of the 350 nm permalloy film with in plane domain (IPD), stripe domain (SD), and labyrinth domain (LD) patterns. Experimental and micromagnetic simulation results showed that the change in magnetic domain structure from IPD to LD was due to the increasing perpendicular magnetic anisotropy (PMA) of the film. The magnetization dynamics indicated that the resonant modes of the film strongly depended on the magnetic domain structure. IPD films presented a uniform precession mode. The film with well-regular SD exhibited clear acoustic and optical resonance modes, and the formation of LD suppressed both resonance modes. Finally, the dynamics of magnetization dependent on the domain structure in these films were discussed by using the phenomenological resonance models.

Magnetic Domain and Magnetic Properties of Tb–Dy–Fe Alloys Directionally Solidified and Heat Treated in High Magnetic Fields

(Tb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.27</sub> Dy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.73</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.04</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.95</sub> alloys directionally solidified in a 4 T high magnetic field were heat treated in various high magnetic fields. Changes in magnetic domain structure, magnetostriction, and magnetization of the alloys were investigated. The alloys treated at 12 T showed the highest magnetostriction, followed in descending order by the alloys treated at 0, 6, 3, and 9 T. The alloys treated at 12 T showed the highest light and dark contrast in the domain image, followed in descending order by the alloys solidified at 6, 0, 3, and 9 T. The change in magnetostriction can be mainly attributed to the alteration of the light and dark contrast in the domain image induced by the high magnetic fields. It can be proved that the high magnetic field can be effectively applied to the directionally solidification and heat treatment processes of Tb-Dy-Fe alloys to improve their magnetostrictive performance.

(Keynote Paper) Mono-Domain Ferrites and Their Implications

Neutron depolarization experiments have shown that the intragranular magnetic domain structure of polycrystalline ferrites exhibits a marked grain size dependence. Below a grain size of around $3~\mu \text{m}$ , the magnetic domain structure changes from the two-domain to the mono-domain state. Ferrites composed of mono-domain grains exhibit low dissipation at megahertz frequencies. This is attributed to the absence of intragranular domain wall movement, i.e., a microscopic origin for dissipation in ferrites has been identified. The implications of this clear observation and evidence for a transition from the mono- to two-domain state in ferrites for micromagnetic theory when a single particle becomes monodomain, as well as for the initial permeability mechanisms in polycrystalline ferrites, are discussed.

Multi-susceptible single-phase BaAlxFe12−xO19 ceramics with both improved magnetic and ferroelectric properties

The structural, electric, and magnetic properties were investigated in multisusceptible BaAlxFe12−xO19 (x = 0, 1, 2, and 3) ceramics. It is found that the magnetic domain structure changes abruptly with the increase in the Al3+ concentration, which is responsible for the abnormal coercivity enhancement and the distinct initial magnetization behavior. Smaller Al3+ doping increases the off-center displacement of Fe3+ ions at the trigonal bipyramid by introducing compressive strain, which thus enhances the stability of the ferroelectric phase and improves the ferroelectric Curie temperature of BaFe12O19. Moreover, more stable Al3+ ions can increase the resistance of BaFe12O19. The present results highlight the possible application of Al3+ doped BaFe12O19 ceramics as a multisusceptible single-phase material on multifunctional electronic devices.

Effects of a Large Content of Yttrium Doping on Microstructure and Magnetostriction of Fe&lt;sub&gt;83&lt;/sub&gt;Ga&lt;sub&gt;17&lt;/sub&gt; Alloy

As-cast (Fe0.83Ga0.17)100-xYx (x=0, 3, 6 and 9) alloys were prepared by non-consumable vacuum arc melting furnace under a protective argon atmosphere. The crystal structures and surface morphologies of the alloys were studied by X-ray diffraction (XRD), optical microscope (OM) and scanning electron microscopy (SEM), combined with energy dispersive spectroscopy (EDS), respectively. The surface domain structures were observed by atomic force microscopy (AFM). The magnetostriction coefficients of the alloys were measured by strain gauging method. The results showed that the as-cast Fe83Ga17 alloy was composed only of a single phase of A2 with bcc structure, whereas the ternary Fe-Ga-Y alloys contain multiphase structure, besides the A2 phase, (FeGa)17Y1.76 new phases are observed as well, and an elemental yttrium phase appeared when the yttrium content increased to x=6 and x=9. Doping with yttrium have an effect on the change of magnetic domain structure of the binary alloy. With increasing x, the magnetostriction coefficient of the (Fe0.83Ga0.17)100-xYx alloys decreased sharply. The minimum magnetostriction coefficient is reduced to 12 ppm at the magnetic field of 426kA/m when x=9.

Engineering of Magnetic Properties of Fe-Rich Microwires by Stress Annealing

We present our experimental results on optimization of the magnetic softness in Fe-rich magnetic microwires by stress annealing. It is found that the magnetic softness and magnetoimpedance effect of the Fe-rich microwires can be considerably improved by annealing. The hysteretic properties and magnetoimpedance are considerably affected by the tensile stress applied during the annealing. Experimental dependencies are attributed to changes in magnetic domain structure of magnetic wires in particular decrease of the inner axially magnetized core volume in expense of increase of the outer domain shell with transverse magnetization orientation. Observed stress-induced anisotropy and related changes of magnetic properties are discussed considering internal stresses relaxation and “back-stresses.”

Interlayer coupling in symmetric and asymmetric CoFeB based trilayer films with different domain structures: Role of spacer layer and temperature

We report the study of interlayer coupling between Co20Fe60B20 (CoFeB262) layers and the resulting magnetic properties of trilayer [CoFeB262 (y nm)/Cr (x nm)/CoFeB262 (20 nm)] films with symmetric (y = 20) and asymmetric (y = 100) structures. All as-deposited CoFeB262 films exhibit amorphous structure. Surface topography studies display clear and uniform surfaces with very fine and sparsely dispersed nanosized grains. The average surface roughness of the CoFeB262 films increases marginally as y is increased from 20 to 100 nm. The shape of magnetic hysteresis (M-H) loop of single-layer CoFeB262 (y nm) films transforms from rectangular shape for CoFeB262 (20 nm) film to transcritical one for CoFeB262 (100 nm) film. This is mainly due to change in magnetic domain structure from in-plane magnetization to dense stripe domain with increase in y. On the other hand, the shape of the M-H loops in trilayer films strongly depends on x, y and temperature. All symmetric trilayer films show single magnetization reversal process at room temperature with a kink in the first quadrant for films with x < 1. Coercivity (HC), saturation field (Hsat) and remanence ratio (MR/MS) show oscillatory behaviors as a function of x. For asymmetric films, the transcritical loop changes into rectangular one after the introduction of Cr interlayer. This also causes a large reduction in Hsat and enhances MR/MS sharply. Temperature dependent M-H loops at low temperatures reveal the disappearance of the kink in symmetric trilayer films and the formation of additional steps in asymmetric trilayer films with x > 0.5. The relative increase in HC with decreasing temperature is found to be larger for symmetric films as compared to asymmetric ones. The observed results are explained on the basis of change in the interlayer coupling between CoFeB262 layers with change in x, y and temperature dependent interfacial strain, which modifies the nature of interlayer coupling. These results also demonstrate that dense stripe domain of thicker CoFeB262 layers can be easily converted into simple in-plane magnetization using trilayer thin films.

Change in Magnetic Domain Structure of Nd‐Fe‐B Sintered Magnets by Compressive Stress

SUMMARYTo clarify the relationship between compressive stresses and demagnetization of Nd‐Fe‐B sintered magnets, we have examined the change in domain configuration by compressive stresses using a Kerr microscope. The magnetic domains of five kinds of Nd‐Fe‐B sintered magnets have been observed. The magnets have a coercivity of 0.8 MA/m to 1.4 MA/m and residual magnetic flux density of 1.3 T to 1.5 T. Irreversible demagnetization of Nd‐Fe‐B magnets with a low coercivity of 0.875 MA/m and high residual magnetic flux density of 1.41 T to 1.47 T have occurred from applying a compressive stress of 100 MPa. The compression‐affected area is approximately 0.14%. The stress more than 50 MPa is needed to demagnetize Nd‐Fe‐B magnets. The amount of irreversible demagnetization depends upon the intensity of the compressive stress as well as the residual magnetic flux and coercive force of the magnets.

Change of magnetic domain structure by mechanically induced twin boundary motion in Ni-Mn-Ga single crystal

The single variant state exhibits usual labyrinth and band magnetic domains depending on orientation of easy magnetization axis. By the passage of single twin boundary induced by mechanical stress the rake and granular domain patterns are formed. These domain patterns are further modified by repeated passage of the twin boundary resulting in similar domain patterns in the sample even though the orientation of the magnetization is different.

Effects of composition, thickness and temperature on the magnetic properties of amorphous CoFeB thin films

We report composition, thickness and temperature dependent magnetic properties of amorphous Co80-yFeyB20 (x nm) films with y = 40,60 and x = 7–200 nm prepared directly on thermally oxidized Si substrate using magnetron sputtering technique. All the as-deposited films exhibit amorphous structure. For both the compositions, the shape of magnetic hysteresis (M-H) loops strongly depends on their thicknesses, i.e., the films with x ≤ 20 exhibit either rectangular shape or flat type loops, which change into transcritical type beyond a critical thickness (x > 50). Room temperature coercivity (HC) and field required for saturation (HS) increase almost linearly with increasing x between 7 and 20, but exhibit a rapid increase for the films with x up to 100 and then decrease slightly for x = 200 film. Thickness dependence of HC and HS varies also with composition. This is attributed to the development of effective magnetic anisotropy (Keff) with increasing film thickness, which causes a change in magnetic domain structure from in-plane magnetization to stripe domains and degrades the magnetic properties above critical thickness. Temperature dependent M-H loops reveal that the loop shapes do not change with temperature for a given film. However, the values of HC and HS increase with decreasing temperature and the rate of increase depends on the composition and thickness. Similarly, the variation of Keff with temperature also displays a considerable dependency on the composition. The observed results are discussed on the basis of development of compositional and thickness dependent effective magnetic anisotropy, which changes the magnetic domain structure with increasing CoFeB film thickness.

Hydrostatic pressure effect on magnetic hysteresis parameters of pseudo‐single‐domain magnetite

AbstractThis paper reports the first in situ magnetic hysteresis measurements of pseudo‐single‐domain (PSD) magnetite under high pressure up to 1 GPa. The magnetic hysteresis measurements of stoichiometric PSD magnetite samples under hydrostatic pressure were carried out using a piston‐cylinder high‐pressure cell, and the pressure dependence of the hysteresis parameters of PSD magnetite was calculated from the hysteresis curves. It was found that coercivity (Bc) increases with increasing pressure as a quadratic function up to 1 GPa by ∼90%, which is different from the pressure dependences of Bc of multidomain and single‐domain magnetites. Coercivity of remanence also increases as a quadratic function, and saturation remanence (Mrs) increases with pressure up to 0.5 GPa by ∼20% until reaching saturation. In contrast, saturation magnetization is constant up to 1 GPa. The approximate demagnetizing factor calculated from the ratio Bc/Mrs increases with increasing pressure, suggesting that the number of lamellar domains increases with increasing pressure. The number of lamellar domains and domain wall width are theoretically estimated to increase under high pressure due to the changes in magnetostriction, elastic, and magnetocrystalline anisotropy constants, and these changes in magnetic domain structure should relate to the changes in the magnetic properties of PSD magnetite.

Changes in magnetic domain structure during twin boundary motion in single crystal Ni-Mn-Ga exhibiting magnetic shape memory effect

The complexity of Ni-Mn-Ga single crystal originates from the interplay between ferromagnetic domain structure and ferroelastic twinned microstructure. Magnetic domain structure in the vicinity of single twin boundary was studied using magneto-optical indicator film and magnetic force microscopy technique. The single twin boundary of Type I was formed mechanically and an initial magnetization state in both variants were restored by local application of magnetic field (≈40 kA/m). The differently oriented variants exhibited either stripe or labyrinth magnetic domain pattern in agreement with the uniaxial magnetocrystalline anisotropy of the martensite. The twin boundary was then moved by compressive or tensile stress. The passage of the boundary resulted in the formation of granular or rake domains, respectively. Additionally, the specific magnetic domains pattern projected by twin boundary gradually vanished during twin boundary motion.

Influence of Laser-Induced Surface Morphology on the Magnetic Domains of CoFeSiB Amorphous Ribbons

To investigate the relationship between magnetic domain structure and morphology variations induced by laser processing, Co 68.15Fe 4.35Si 12.5 B 15 amorphous ribbons were irradiated by a 1064-nm pulsed Nd:YAG laser in air. The illumination was performed at various pulse repetition rates which as a key parameter can effectively change the morphology of ribbons. The morphology and magnetic domain structure changes were correlated with magnetic force microscopy. It was shown that depending on the pulse repetition rate, various surface morphologies can be induced, which in turn may cause transformation of magnetic domains, anisotropy induction, and also pinning of magnetic domain walls.

Surface relief and domain structure of ferromagnetic shape memory alloys

A study is made of the surface corrugation during thermal cycling of ferromagnetic shape memory alloys (FSMA). This specific feature is a property of FSMA alloys and is a consequence of martensitic phase transformations not necessarily connected with surface defects of the material. The surface relief structure was studied together with martensite and magnetic domain structure changes during thermal cycling of the samples with the aid of differential polarized light microscopy. The analysis was facilitated making use of auxiliary reference grids applied to the surface of the samples.

力学的劣化・損傷を生じた電磁鋼板の磁気損失の評価

The evaluation of magnetic properties of fatigue-damaged specimens of electromagnetic steel sheets have been investigated. In low-cycle fatigue tests, plastic deformation occurred all over the specimen. In macro-magnetic measurement using B-H analyzer, magnetic properties such as iron loss were remarkably deteriorated. By observing magnetic domain structure using magneto-optical Kerr microscope, the width of magnetic domain decreased and the distribution of magnetic domain became random. In high-cycle fatigue tests, magnetic properties were also deteriorated in fatigue-damaged and especially in fatigue-cracked specimens. By observing specimen surface using laser scanning microscope some grains around notch or fatigue crack were plastically deformed. And in these plastically deformed grains, the width of magnetic domain decreased and the distribution of magnetic domain became random. Then the change of magnetic domain structure in plastically deformed region seems to be the main cause of deterioration of the magnetic properties both in low-cycle and high-cycle fatigue damaged specimens.

Visualization of magnetic domain structure changes induced by interfacial strain in CoFe2O4/BaTiO3 heterostructures

We visualized the evolution of the magnetic domain structure in CoFe2O4 films on different structural phases of BaTiO3 substrates with {0 0 1} orientation, using variable temperature magnetic force microscopy. When BaTiO3 underwent transitions from rhombohedral to orthorhombic to and from orthorhombic to tetragonal structures with increasing temperature, only local variations to the magnetic domains were observed. At the BaTiO3 tetragonal–cubic transition however, the magnetic domain size increased by 75% with an overall decrease in stray field contrast (33% decrease) because of reorientation of the magnetization to the in-plane directions. The reorientation of magnetization during the tetragonal to cubic phase transition of BaTiO3 was induced by release of asymmetric interfacial strain between the CoFe2O4 film and the BaTiO3 substrate, as non-uniformly distributed a and c surface ferroelectric domains in the BaTiO3 tetragonal phase disappeared at the paraelectric BaTiO3 cubic phase transition. Strain analysis based on macroscopic magnetization measurements was correlated with the microscopic magnetic domain structure to help understand the coupling in two-phase multiferroicheterostructure mediated by interfacial strain.

Anisotropic magnetoresistance in low-doped La0.78Ca0.22MnO3 crystals

Unusual behavior of anisotropic magnetoresistance (AMR) has been encountered in low-doped La0.78Ca0.22MnO3 single crystals. In contrast with previous studies of AMR in manganites, as the maximal effect was observed around TC, the AMR of La0.78Ca0.22MnO3 single crystals (TC ≈ 189 K) increases monotonously with decreasing temperature, reaches a maximum around 140 K, and then decreases with further temperature decrease. Moreover, around the maximum, AMR increases almost linearly with magnetic fields and only at fields exceeding H ∼ 7 kOe does it start to saturate. The observed unusual enhancement of AMR may be ascribed to the changes in magnetic domain structure at temperatures below 150 K as observed previously by us using a magneto-optical imaging technique.

Preparation of one-dimensional Ni0.5Zn0.5Fe2O4/SiO2 composite nanostructures and their magnetic properties

The Ni0.5Zn0.5Fe2O4/SiO2 composite nanofibers were prepared using sol-gel process combined with electrospinning. The thermal decomposition and phase inversion process of precursor nanofibers and the effects of calcination temperature and SiO2 content on the phase composition, microstructure, morphology and magnetic property of the resulting nanofibers were studied by means of thermogravimetric and differential thermal analysis, X-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy and vibrating sample magnetometer. The experimental results show that the cubic spinel structure is basically formed when the precursor nanofibers are calcined at 450 ℃ for 2 h. The average grain size of Ni0.5Zn0.5Fe2O4 contained in the composite nanofibers with 10 % SiO2 and their specific saturation magnetization and coercivity increase with increasing calcination temperature. Amorphous SiO2 additive can effectively restrain the growth of Ni0.5Zn0.5Fe2O4 nanocrystals. As a result, with SiO2 content increasing from 0 to 20 % , the average grain size of Ni0.5Zn0.5Fe2O4 in the prepared Ni0.5Zn0.5Fe2O4/SiO2 composite nanofibers calcined at 900 ℃ for 2 h decreases from 81.6 to 13.3 nm, and the specific saturation magnetization of these samples monotonically decreases, whereas the coercivity initially increases and then decreases due to the change of magnetic domain structure from multi-domain to single-domain along with the reduction in grain size. In addition, with the increase of SiO2 content, the diameter of the as-prepared Ni0.5Zn0.5Fe2O4/SiO2 composite nanofibers gradually increases and the surface becomes smooth.

Kerr Microscopy Study of Magnetic Domain Structure Changes in Amorphous Microwires

In this paper, we report investigations on circular magnetic domain structure in amorphous microwires. Polar magneto-optical Kerr microscopy was used for the observation of the magnetic domains images. The surface magnetization reversal is determined basically by the circular domains nucleation. For the first time, the rearrangement of the surface domain structure is observed as a part of the magnetization reversal process in amorphous microwires.