Surface Magnetic Domain Research Articles

In-situ visualization of stress-dependent bulk magnetic domain formation by neutron grating interferometry

The performance and degree of efficiency of industrial transformers are directly influenced by the magnetic properties of high-permeability steel laminations (HPSLs). Industrial transformer cores are built of stacks of single HPSLs. While the insulating coating on each HPSL reduces eddy-current losses in the transformer core, the coating also induces favorable inter-granular tensile stresses that significantly influence the underlying magnetic domain structure. Here, we show that the neutron dark-field image can be used to analyze the influence of the coating on the volume and supplementary surface magnetic domain structures. To visualize the stress effect of the coating on the bulk domain formation, we used an uncoated HPSL and stepwise increased the applied external tensile stress up to 20 MPa. We imaged the domain configuration of the intermediate stress states and were able to reproduce the original domain structure of the coated state. Furthermore, we were able to visualize how the applied stresses lead to a refinement of the volume domain structure and the suppression and reoccurrence of supplementary domains.

Magnetic surface domain imaging of uncapped epitaxial FeRh(001) thin films across the temperature-induced metamagnetic transition

The surface magnetic domain structure of uncapped epitaxial FeRh/MgO(001) thin films was imaged by in-situ scanning electron microscopy with polarization analysis (SEMPA) at various temperatures between 122 and 450 K. This temperature range covers the temperature-driven antiferromagnetic-to-ferromagnetic phase transition in the body of the films that was observed in-situ by means of the more depth-sensitive magneto-optical Kerr effect. The SEMPA images confirm that the interfacial ferromagnetism coexisting with the antiferromagnetic phase inside the film is an intrinsic property of the FeRh(001) surface. Furthermore, the SEMPA data display a reduction of the in-plane magnetization occuring well above the phase transition temperature which, thus, is not related to the volume expansion at the phase transition. This observation is interpreted as a spin reorientation of the surface magnetization for which we propose a possible mechanism based on temperature-dependent tetragonal distortion due to different thermal expansion coefficients of MgO and FeRh.

Influence of microstructure evolution on GMI properties and magnetic domains of melt-extracted Zr-doped amorphous wires with accumulated DC annealing

Herein, we reported the influences of accumulated direct current annealing (ADA) on the GMI properties and microstructures of Zr-doped melt-extracted (Co68.15Fe4.35Si12.25B12.25Zr3) amorphous microwires. There indicated that ADA-ed wires enhanced GMI properties and improved the microstructures remarkably in comparison with as-fabricated wires. The maximum GMI ratio [ΔZ/Z0]max and equivalent magnetic circumferential anisotropy field (EMCAF) of ADA-ed microwires were increased to 256.01% and 4Oe at 20MHz, respectively, which are more than nearly 8 and 2times of 33.62% and 1.6Oe for as-fabricated wires, respectively. Moreover, the maximum magnetic field response sensitivity (ξmax) increased to 372.57%/Oe, which is much higher than the as-fabricated wires of 44.71%/Oe. The remarkable enhancement of GMI performance was considered as the microstructural evolution including structural relaxation, appearance of nano-crystallization, and circumferential arrangement of surface magnetic domains. Nano-crystallization degree and circumferential magnetic domains arrangement were effectively improved by actions of Joule thermal energy and circular magnetic field generated ADA as shown in HRTEM and magnetic force microscope (MFM) analysis. Based on above, both the excellent GMI performances and relatively large ξmax values indicate the ADA is an effective annealing technique for thermal treating the melt-extracted amorphous wires which applied for potentially magnetic sensor in detecting low-intensity magnetic fields.

Transformation of magnetic structure in amorphous microwires induced by temperature and high frequency magnetic field

The study of the magnetic properties of glass-covered amorphous microwires is reported. This study is focused on the influence of a high frequency electric current and of temperature upon the surface magnetic domain structure. Investigations are performed using the magneto-optical Kerr effect technique, and it is found that the high frequency current and heating process have a great and essential influence upon the surface magnetization reversal and surface domain structure. The induced formation and transformation of the surface magnetic structure are key processes that determine the stable operation of giant magneto-impedance devices.

高輝度・高スピン偏極低エネルギー電子顕微鏡による表面磁区の動的観察

高輝度・高スピン偏極低エネルギー電子顕微鏡による表面磁区の動的観察

Direct imaging of the magnetization reversal in microwires using all-MOKE microscopy.

We report a method of imaging of the magnetization reversal process using analysis of real-time images of magnetic domain structures in cylindrically shaped microwires. This method uses wide-field polarizing optical microscopy and is based on the magneto-optical Kerr effect (MOKE). The aperture diaphragm in MOKE microscope was used to control the incident angles of the light rays that reached the non-planar surface of the microwire and also determined the MOKE geometries. The movement of the non-central position of the hole in this diaphragm leads to a change in the orientation of the plane of incidence of the light along the perpendicular or the parallel direction to the axial direction of the wire. The visualization of the surface magnetic domain structures is obtained using polar and longitudinal MOKE geometries. The hysteresis loops were obtained by plotting the averaged image contrast as a function of the external magnetic field. The separation of the all-magnetization components is performed using different MOKE geometries in a microscope. We demonstrate the use of vector magnetometry to analyze the orientation of the magnetization in a cylindrically shaped microwire under the influence of an external magnetic field.

Near surface magnetic domain observation with ultra-high resolution.

Near field magnetic force microscopy (NF-MFM) has been demonstrated to locally observe the magnetic fine structures in nanosized recording bits at an operating distance of 1 nm. The nanoscale magnetic domains, the polarity of surface magnetic charges, as well as the 3D magnetic fields leaking from the bits are investigated via NF-MFM with a soft NiFe tip. A Fourier analysis of the images suggests that the magnetic moment can be determined locally in a volume as small as 5 nanometers. The NF-MFM is crucial to the analysis of surface magnetic features and allows a wide range of future applications, for example, in data storage and biomedicine.

Cryogenic Joule annealing induced large magnetic field response of Co-based microwires for giant magneto-impedance sensor applications

We have presented herein the results of microstructure, surface magnetic domains (SMDs), and giant magneto-impedance (GMI) effect of melt-extracted Co68.15Fe4.35Si12.25B11.25Nb2Cu2 amorphous wires for the first time employed by using a cryogenic Joule annealing (CJA) technique with large DC current amplitude. Compared with the conventional JA method, experimental results indicate that the maximum GMI ratio [ΔZ/Z0]max achieves up to 425% at 8.1 MHz with monotonic increase of the axial magnetic field Hex up to 6.5 Oe for 300 mA (equal to around 1.06 × 106 A/dm−2) CJA-ed wire, which is about 75% larger than the [ΔZ/Z0]max for the 100 mA (nearly 3.53 × 105 A/dm−2) JA-ed microwires. The remarkable features of large and linearly sensitive response field (2.5 ∼ 6.5 Oe) and the sensitivity of 99.4%/Oe with higher GMI ratio simultaneously make the CJA tailored melt-extracted microwires promising candidate materials for miniaturized GMI sensors. Another interesting result of GMI profiles of 200 mA (appropriately equal to 7.07 × 105 A/dm−2) CJA-ed wire show a linear response to Hex (ranging from 10 to 80 Oe or more), this behavior of GMI curves can be explored to fabricate bi-sensor. Large response field proves to originate from the intensive coupling between the radial stress field and the circumferential magnetic field during CJA process. The effect of outer-shell microstructure and complex SMD for 300 mA CJA-ed microwire is attributed to the fact that liquid nitrogen hinders the evolution of circumferential domain structure to some extent and protects the amorphous structure in the shell region.

An interchangeable scanning Hall probe/scanning SQUID microscope.

We have constructed a scanning probe microscope for magnetic imaging, which can function as a scanning Hall probe microscope (SHPM) and as a scanning SQUID microscope (SSM). The scanning scheme, applicable to SHPM and SSM, consists of a mechanical positioning (sub) micron-XY stage and a flexible direct contact to the sample without a feedback control system for the Z-axis. With the interchangeable capability of operating two distinct scanning modes, our microscope can incorporate the advantageous functionalities of the SHPM and SSM with large scan range up to millimeter, high spatial resolution (⩽4 μm), and high field sensitivity in a wide range of temperature (4.2 K-300 K) and magnetic field (10(-7) T-1 T). To demonstrate the capabilities of the system, we present magnetic images scanned with SHPM and SSM, including a RbFeB magnet and a nickel grid pattern at room temperature, surface magnetic domain structures of a La(2/3)Ca(1/3)MnO3 thin film at 77 K, and superconducting vortices in a striped niobium film at 4.2 K.

Surface topography, microstructure and magnetic domains in Al for Sn substituted metamagnetic Ni–Mn–Sn Heusler alloy ribbons

Heusler alloy Ni48Mn39.5Sn12.5−xAlx (x = 0, 1, 2,3) ribbons were prepared by melt spinning. The cross section of ribbons reveals a typical heterogeneous microstructure consisting of small equi-axed and columnar grains. The top and bottom ribbons sides are homogenous in composition but they differ in terms of surface structure. The wheel ribbon side appears smoother and shows some degree of macroscopic organization. On the other hand the free ribbon surface regardless of composition shows a more complex morphology consisting of small equi-axed grains, larger grains forming clusters and conical sub crystal structures. A characteristic twinned plate like microstructure confirming the presence of an increased amount of martensite has been observed for the Ni48Mn39.5Sn9.5Al3 ribbon. The martensitic plates are 70–100 nm in size. The phase shift of 0.5° was detected, while scanning the latter ribbon sample in magnetic force microscope mode, indicating the existence of a magnetic multi-domain structure in this sample.

Magnetic domain structure and crystallographic orientation of electrical steels revealed by a forescatter detector and electron backscatter diffraction.

The magnetic properties of non-oriented electrical steels (NOES) are an important factor in determining the efficiency of electric vehicle drivetrains. Due to the highly variable texture of NOES, the relationships between crystal orientation, the magnetic domain structure, and the final magnetic properties are complicated and not fully understood. In this study, a NOES sample was characterized with a method capable of imaging surface magnetic domains using scanning electron microscopy (SEM) with an electron backscatter diffraction (EBSD) system equipped with a forescatter detector. This method used type II magnetic contrast without a specialized SEM setup, and imaged with a resolution limit of approximately 250-300nm. The domain structure of the NOES sample was successfully related to β, which was defined as the angle between the closest magnetic easy axis and the surface of the sample (the RD-TD plane). However, it was shown that if the easy axes were aligned between neighbouring grains with respect to the grain boundary normal, the domain structure could align with an easy axis that was not the closest to the surface, and complex domain structures could be become wider. This structure and width change of complex domain structures has not been previously observed from single crystal or large-grained material studies. The successful application of this method to reveal the influence of surrounding grains can be used to better understand the magnetic properties of NOES.

Surface magnetic domains dynamic in machined steel

This contribution deals with an observation of the magnetic dynamic of different types of the machined surface of bearing steel. The Bakhausen noise (BN) measurements are presented here as commonly introduced in industry for quality control due to the extremely sensitivity of the magnetic domains wall dynamics to the microstructure of material. The results of magneto-optical measurements are presented with the goal to explain the observed BN anisotropy. It is shown that BN anisotropy is associated with uniaxal magnetic anisotropy introduced by hard milling which causes the principally different magnetic reversals processes in orthogonal directions.

Nanoscale Dynamic Behavior of Surface Magnetic Domains on a La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB> Thin Film

An oscillating magnetic tip can be used to induce the striped magnetic ripple pattern with alternating up-and-down striped magnetic domains on a ferromagnetic La0.7Sr0.3MnO3 (LSMO) thin film surface. Magnetic force microscopy (MFM) images show that the surface magnetic domains (SMDs) can be aligned in a well-ordered alternating up-and-down c(2 x 2) structure on the stripe magnetic domains, indicating that the oscillating magnetic tip turns the ferromagnetic LSMO surface into a canted antiferromagnetic state. The orientation of the SMDs is determined by their discrete phase distribution. A three-dimensional (3D) SMD orientation model is built to understand dynamic behavior of the SMDs.

Surface and internal magnetic domain structures of Fe-Ga alloy rods

The magnetic domain structures of the 〈100〉 oriented Fe81Ga19 polycrystalline alloys with rapid quenching (RQ) and post-annealing (PA) thermal treatments are investigated by using magnetic force microscopy (MFM). The surfaces of the RQ alloy rods take on the dendritic domains after undergoing a standard mechanical polishing. While after PA processing, the distinct domain structures are observed at different temperatures. The wide stripe-like domain patterns appear in the surface of those PA rods at 550°C while the ramous domains remain at 400°C annealing. X-ray diffraction patterns indicate that a thin iron layer is formed on the surface of the specimens annealed at higher temperature. The soft magnetic iron layer, actually acting as a shield for the stray fields emerging from the internal magnetic structures underneath, brings about the presentation of the wide internal domains.

Microscopic investigation of surface and interfacial magnetic domain structure of Fe–NiO(1 0 0) system

We report our experimental observation of microscopic modification, reconstruction and evolution of the antiferromagnetic domain structure of the NiO(1 0 0) surface in view of the exchange bias effect. Some domain patterns (called non-equilibrium domains) as observed on the as-cleaved surface do not follow the well-known bulk symmetry traces on the (1 0 0) surface. But, bulk-terminated domains (called equilibrium domains) are found to be renucleated up on cooling the sample from above the Néel temperature, unless domains are strongly pinned by crystalline defects. We also observe certain domain evolution after annealing the crystal at various temperatures above the Néel temperature. Influence of growth condition on the ferromagnetic domain structure of the Fe film deposited on NiO(1 0 0) has been followed in situ. While for thin film case (7 ML), no influence of growth has been observed, for thicker film (21 ML) the Fe domain structure is found to be determined by both growth-induced and exchange anisotropy. Thus, our observations depict a thickness-dependent interplay between growth-induced and exchange anisotropy in ferromagnetic film grown on the antiferromagnetic substrate.

Surface magnetization reversal and magnetic domain structure in amorphous microwires

AbstractThis paper presents a review on magneto‐optical investigations of the glass‐coated amorphous microwires including magneto‐optical magnetometry and microscopy. We also discuss a Kerr‐effect method of domain‐wall‐motion detection in glass‐coated wires within a classical Sixtus–Tonks experimental scheme. The developed techniques make it possible to observe the surface magnetization reversal and to establish the main mechanisms of domain‐structure formation and transformation.

Creation and Manipulation of Surface Magnetic Domains in an Alternating Up-and-Down Pattern

According to Lenz's law, the magnetic field from the oscillating magnetic probe will induce out-of-plane surface magnetic domains (SMDs) from the in-plane magnetization at the locally tapped points on a ferromagnetic La(0.7)Sr(0.3)MnO3 (LSMO) thin film. It was possible to control and manipulate the out-of-plane SMDs by varying the tapping intervals and changing the scanning direction. We also found that the anisotropic stresses from the out-of-plane SMDs caused the appearance of large-area straight striped domain structures on the order of several micrometers. Smaller oscillating magnetic probe tapping intervals produced larger periods (or widths) of the straight striped domain structure.

Surface magnetic properties and domains observation in as-quenched and annealed FeNbB ribbons

The longitudinal magneto-optical Kerr effect (MOKE) combined with the magneto-optical microscopy is used to investigate the surface magnetic anisotropy and the domain behavior in as-quenched (AQ) and strain-annealed (SA) FeNbB ribbons. X-ray diffraction, conversion electron Mössbauer spectroscopy (CEMS), and scanning electron microscopy (SEM) confirmed the existence of approximately 1.3 μ m thick magnetically harder layer on the ribbon air side, consisting of crystallites embedded in an amorphous matrix. The underneath bulk phase is amorphous and magnetically soft. Residual anisotropies and the domain patterns (wide in-plane domains with 180 ∘ walls and narrow fingerprint domains) corresponding to amorphous phase are mainly caused by the internal stresses originating from the rapid quenching process. In the surface crystalline phase they are gradually overlapped by strip domains with magnetization directions almost perpendicular to the ribbon axis. The anisotropy changes caused by additional annealing and straining of the samples are shown and discussed in detail.

Thickness dependent magnetic and structural properties of Co films grown on GaAs (100)

The structural, magnetic and transport properties measurements carried out on Co thin films deposited by electron beam evaporation on GaAs substrate as a function of layer thickness ranging from 50 Å to 1000 Å are presented here. Structural measurements show the film to be amorphous in nature at lower thickness which becomes crystalline at higher thickness. Magnetic measurements show an increase in saturation magnetization (M S) with film thickness. M S values are found to vary from 521 emu/cm 3 to 1180 emu/cm 3 for thicknesses ranging from 50 Å to 1000 Å. The coercivity and saturation field value shows a systematic decrease up to 600 Å thickness and increase thereafter. Various microstructural parameters were also calculated using GIXRR technique. A clear grain growth is observed in AFM technique with film thickness and its influence on transport properties was also seen. Different surface morphology and magnetic domain structures were obtained on different thin film samples by AFM and MFM techniques, respectively. XPS measurements reveal formation of CoAs phase at the interface between Co and GaAs. All these results are discussed and interpreted in detail in this communication.

Influence of Annealing on the Magnetic Properties of Fe<sub>50</sub>Co<sub>50</sub> Films

The Fe50Co50 magnetic films were prepared by magnetron sputtering onto glass substrates. The structural and magnetic properties of the films were investigated as a function of annealing temperature and annealing time. It is found that the films have the better crystallization orientation after annealing. The in-plane coercivity Hc reduces with increasing annealing temperature and annealing time. Coercivity reaches the minimum in the sample annealed at 600°C for 2h. Meanwhile, the saturation magnetization Ms increases with increasing annealing temperature as a whole. A scanning probe microscope was used to scan surface morphology and magnetic domain structures. After annealing, the domain size becomes larger and the contrast of domains increases.