Surface Magnetic Domain Research Articles

Magnetic properties and magnetic domains of Nd–Fe–B thin films

Anisotropic Nd–Fe–B thin films are fabricated by direct current magnetron sputtering on Si substrates heated to temperatures over a wide range. Surface morphology and magnetic domains of the Nd–Fe–B thin films prepared at different sputtering temperatures (25–600 °C) are observed by a scanning probe microscopy. The magnetic domains exhibit a rich variety of textures, changing from striped via maze to cloudlike as the sputtering temperature is increased. Variations in magnetic domains with substrate temperature are discussed using phase components and magnetic anisotropies of the thin films. In addition, patterns of magnetic domains are analyzed using the “disorder functions,” a set of characterizations of complex patterns with labyrinthine structures. The disorder function δ(1) and the structure factor δk do not change appreciably until a substrate temperature of 350 °C, but increases significantly beyond 400 °C. The disorder in magnetic domains increases with increasing sputtering temperature. A simultaneous enhancement of the anisotropic c texture and the hard-magnetic properties of the thin films are observed. The significant change of the disorder function at Ts=400 °C appears to be a precursor to the hardening of the Nd–Fe–B film. The most disordered magnetic domains of the film with the substrate temperature of 600 °C correspond to the optimum magnetic properties, with the maximum energy product (BH)max of 22.4 MG Oe.

Magnetic state ofLa1.36Sr1.64Mn2O7probed by magnetic force microscopy

We have investigated the ferromagnetic (FM) domain structure of a single-crystal bilayered manganite ${\mathrm{La}}_{2\ensuremath{-}2x}{\mathrm{Sr}}_{1+2x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ $(x=0.32)$ by using low-temperature magnetic force microscopy. We observed that below $65\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the FM domains form stable treelike patterns with out-of-plane magnetization. With increasing temperature, the FM domain patterns gradually change in the form of domain wall motion. Above $80\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the FM domain patterns change more and more with each temperature step. The magnetization changes from the out-of-plane to an in-plane direction around $88\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The in-plane FM domains almost completely disappear near the Curie temperature of this sample $({T}_{C}\ensuremath{\approx}110\phantom{\rule{0.3em}{0ex}}\mathrm{K})$, where the resistivity exhibits a sharp increase. We also observed large changes in the magnetic structures upon thermal cycling. We concluded that the formation of FM domains at low temperatures $(T<80\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ is determined by the energy associated with surface magnetic free poles and domain walls. At high temperatures $(80\phantom{\rule{0.3em}{0ex}}\mathrm{K}<T<{T}_{C})$, the two-dimensional FM fluctuations in the basal plane may also play an important role in forming the domain structures. The evolution of the FM domain patterns with temperature coincides with the change in resistivity.

Variable temperature magnetic force microscopy of La<SUB align=right>2/3Sr<SUB align=right>1/3MnO<SUB align=right>3 thin films grown on (LaAlO<SUB align=right>3)<SUB align

The surface magnetic domain patterns of a La2/3Sr1/3MnO3 film grown on a LSAT (001) substrate, where LSAT stands for (LaAlO3)0.3(Sr2AlTaO6)0.7, were observed by magnetic force microscopy (MFM) as a function of the temperature in the 300?360 K range at its remanent state. Magnetic stripe domains showing an up and down magnetic configuration were observed, thus indicating the existence of a small out-of-plane magnetisation component. The domain size was in the order of 300 nm and did not vary with temperature. However the magnetic contrast in the MFM phase images decreased as the temperature increased and vanished as it approached the Curie temperature of the film. MFM measurements were compared with magnetisation vs. temperature curves measured by superconducting quantum interference device magnetometer.

Microstructure and Magnetic Properties of Ag/Fe/Ag Pseudo-Sandwich Nanogranular Films

Nanogranular Ag/Fe/Ag films were prepared by magnetron sputtering from a silver and an iron target onto glass substrates at room temperature and subsequent in situ annealing. The structural and magnetic properties of the films were investigated as a function of silver layer thickness and annealing temperature. X-ray diffraction shows the Fe(110) peak is formed in all the samples. Vibrating sample magnetometer measurements indicate that the magnetic moments lie well perpendicular to the film plane. Coercivity reaches the maximum in the sample annealed at 500C for 30 min with 3 nm Ag layer. A scanning probe microscope was used to scan surface morphology and magnetic domain structures. In as-deposited samples the average grain size and the average roughness is smaller than that the annealing samples. After annealing, the grain size is larger and the contrast of domains increases, but the domain size becomes smaller.

Surface and Interior Magnetic Domain Structures of $\langle 110 \rangle$ Oriented Tb–Dy–Fe Alloy Rods

We investigated the surface and interior magnetic domains by using magnetic force microscopy for two types of Tb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> Dy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7 </sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.95</sub> crystal growing along the lang110rang direction: 1) crystals annealed at 673 K for 2 h in higher vacuum (5times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> Pa) and 2) crystals annealed at 723 K for 2 h in lower vacuum (5times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> Pa). For the former, we observed fine stripe-like domains at the surface. For the latter, we observed the interior domains of the specimen; these were also stripe-like, but with larger average width than the surface domains. X-ray diffraction patterns indicate the formation of a thin iron layer in the surface of the specimens annealed in the lower vacuum. The iron layer, as a "capping" layer, actually acts as a shielding layer for the stray fields emerging from the interior domains underneath, resulting in the wide interior domains

Effects on the structural and magnetic properties of amorphous ribbons of (Co0.94Fe0.06)72.5Si12.5B15 caused by 4 MeV Cl2+ ion irradiation

The use of energetic ion irradiation to modify magnetic materials has attracted increasing interest in recent years. The possibility of patterning surfaces on these materials offers a wide range of potential applications particularly in technologies related to magnetic storage media, sensing devices and electromagnetic shielding materials. In this work, ultrasoft non-magnetostrictive (Co0.94Fe0.06)72.5Si12.5B15 amorphous ribbons, 50μm thick and 0.85mm wide, fabricated by the chilly block melt spinning technique are irradiated, in their amorphous state, by 4MeV Cl2+ ions with a fluence of 5×1013cm−2. The hysteresis properties of both irradiated and non-irradiated samples are characterized by means of a vibrating sample magnetometer while surface magnetic domain structure is observed by Bitter technique. The presence of an induced magnetic anisotropy in irradiated samples is ascribed to the local damage, caused by ion irradiation treatment, which results in modified coercive field and permeability of the samples. X-ray diffraction results are presented to confirm the amorphicity of the structure even after irradiation with ions.

Self-assembly of fractal nanowires and stripe magnetic domain on stretchable substrate

Magnetic properties of Ni thin films on polydimethylsiloxane (PDMS) are being studied. The author finds that coercivity of the films grown on PDMS is two to three times higher than their rigid counterpart. Magnetic force microscopy studies show that surface morphology and magnetic domains are quite different on elastic substrate. 5nm thick films do not exhibit planar morphology but rather form very long nanowires. The 50nm thick films exhibit in-plane and canted magnetizations with nonmagnetic disordered regions within the thin films. Study suggests that elastomers coupled with magnetic thin films can give rise to interesting material properties.

Magnetic aftereffect and magnetic force microscopy studies of Fe–B∕FePt-type nanocomposite ribbons

Magnetic aftereffect and surface magnetic domain structure of (Fe0.675Pt0.325)100−xBx(x=12–20) nanocomposites have been investigated for correlating with their corresponding phases and magnetic properties. Exchange-coupling effect between grains is present for all the studied ribbons as evidenced by Henkel plot. The volume fraction of magnetically soft phases decreases with increasing B concentration from x=12 to x=18. It leads to the reduction in the activation volume of the reverse domain. Among all samples, the (Fe0.675Pt0.325)82B18 ribbon having the highest intrinsic coercivity (Hci) exhibits minimum value in activation volume V=1.1×10−18cm3, because it possesses the least volume fraction of the magnetic soft phases, i.e., Fe2B or Fe3B phases. Magnetic force microscopy studies reveal the magnetic domain structures of the ribbons, confirming the existence of strong exchange coupling between magnetic grains.

Effect of Co layer thickness on structural and magnetic properties of C/Co/C films

Granular C/Co/C films have been prepared by magnetron sputtering from C and Co onto glass substrates at room temperature and subsequent in situ annealing. It has been found that the structure and magnetic properties of the C/Co/C films depend strongly on the Co layer thickness. Vibrating sample magnetometer measurements indicate that the in-plane coercivities reach maximum in 20 nm Co thickness of both as-deposited and annealed films. The squareness ratio of annealed films was more than 0.8. X-ray diffraction shows that majority Co nanograins are formed as the hexagonal-close-packed (HCP) structure in 20 nm Co thickness with annealing at 400 °C. Scanning probe microscope was used to scan surface morphology and magnetic domain structures. The values of the surface roughness were lower than 0.6 nm in all annealed samples. The average magnetic cluster size was estimated to be about 10 nm in annealed 20 nm Co thickness films.

Spin-resolved magnetic studies of focused ion beam etched nano-sized magnetic structures

Scanning ion microscopy with polarization analysis (SIMPA) is used to study the spin-resolved surface magnetic structure of nano-sized magnetic systems. SIMPA is utilized for in situ topographic and spin-resolved magnetic domain imaging as well as for focused ion beam (FIB) etching of desired structures in magnetic or non-magnetic systems. Ultra-thin Co films are deposited on surfaces of Si(100) substrates, and ultra-thin, tri-layered, bct Fe(100)/Mn/bct Fe(100) wedged magnetic structures are deposited on fcc Pd(100) substrates. SIMPA experiments clearly show that ion-induced electrons emitted from magnetic surfaces exhibit non-zero electron spin polarization (ESP), whereas electrons emitted from non-magnetic surfaces such as Si and Pd exhibit zero ESP, which can be used to calibrate sputtering rates in situ. We report on new, spin-resolved magnetic microstructures, such as magnetic “C” states and magnetic vortices, found at surfaces of FIB patterned magnetic elements. It is found that FIB milling has a negligible effect on surface magnetic domain and domain wall structures. It is demonstrated that SIMPA can evolve into an important and efficient tool to study magnetic domain, domain wall and other structures as well as to perform magnetic depth profiling of magnetic nano-systems to be used in ultra-high density magnetic recording and in magnetic sensors.

Microstructural and Magnetic Properties of C/Co/C Pseudo-Sandwich Granular Films by Facing Sputtering

Granular C/Co/C films have been prepared by magnetron sputtering from C and Co onto glass substrates at room temperature and subsequent in situ annealing. C and Co targets use an RF and DC facing deposition mode respectively. The structural and magnetic properties of films at room temperature were investigated as functions of Co layer thickness, C layer thickness and annealing temperature. X-ray diffraction (XRD) shows the majority Co nanograins are formed as the hexagonal-close-packed (hcp) structure annealing at 400 °C. Vibrating sample magnetometer (VSM) measurements indicate that the magnetic moment lies well in the film plane. Hc reaches maximum near 20 nm-thick Co layer and 30 nm-thick C layer with annealing temperature of 400 °C for 30 min. Remanent squareness (S) close to 1 was achieved for the film in which C layer thickness is 45 nm. Scanning probe microscope (SPM) was used to scan surface morphology and magnetic domain structures. The average grain size varies from 10 nm to 15 nm after annealing.

Spin polarization of the transport current at the free surface of bulkNiMnSb

The point contact Andreev reflection employing niobium tips was used to determine the degree of transport current spin polarization ( Pt ) at the free surface of bulk NiMnSb at 4.2 K . The data was analyzed within the framework of a modified version of the Blonder, Tinkham, and Klapwijk formulism taking into account the two spin polarized channels in the ferromagnet and treating the interface as a planar delta function barrier of height Z between free electron materials. We find that the measured spin polarization is rather insensitive to different surface preparations and magnetic domain structure, and the maximal value of the Pt at Z=0 is 44% , consistent with recent calculations of the surface reconstruction of NiMnSb . Saturation magnetization of the samples was found to be 3.6 iB per formula unit indicative of a small amount of atomic disorder.

Vortex-type domain structure in Co-rich amorphous wires

Investigation of the surface magnetic domain structure has been performed in Co-rich, nearly zero magnetostrictive, amorphous wires using magneto-optical Kerr effect magnetometry and microscopy. The formation and motion of a multidomain vortex-type structure with curved domain walls have been observed in amorphous wires. The possible origins of the existence of the vortex-type structures in these amorphous wires are discussed.

Determining the spin polarization of surfaces by spin-polarized scanning tunneling spectroscopy

During the last few years, spin-polarized scanning tunneling microscopy and spectroscopy has been developed as a reliable tool to image surface magnetic domain structures of bulk materials as well as thin films and nanostructured systems. In principle, this technique also allows for the determination of the energy-resolved spin polarization of the sample PS(E) with nanometer resolution, information which might play a crucial role in understanding systems like, for example, non-magnetic adatoms on magnetic surfaces. A main problem in quantifying PS(E), however, arises from the fact that, in contrast to planar junctions, the tip–sample distance generally varies with the magnitude and direction of the surface magnetization, since the distance is controlled indirectly by the tunneling current that is itself spin-polarized. We employ a simple model of the tunneling process to investigate this issue and show that a normalization of the dI/dU spectra with the total conductance I/U is insufficient to correct for their distance dependence.

Effects of in situ magnetic field application and post-deposition magnetic annealing on sputtered Fe 50Mn 50/Ni 80Fe 20 bilayers

Effects of in situ magnetic field deposition and post-deposition magnetic annealing on the exchange field and coercivity of Fe 50Mn 50(200 Å)/Ni 80Fe 20 bilayers over a range of 40–120 Å Ni 80Fe 20 thicknesses were investigated. A large increase in coercivity and exchange field was observed in samples that were annealed at 230°C for 15 min in vacuum. The structure with 80 Å Ni 80Fe 20 thickness was found to exhibit maximum exchange field in the range of thickness investigated. The non-monotonic dependence of exchange bias with ferromagnetic layer thickness suggests the important role played by the microstructure of the Fe 50Mn 50 antiferromagnetic AF layer. These phenomena are discussed in relation to surface roughness, grain sizes, diffusion and magnetic domains.

Room temperature scanning Hall probe microscopy of localized magnetic field fluctuations on the surfaces of magnetic recording media, permanent magnets and crystalline garnet films in external bias fields

A sub-micron room temperature scanning Hall probe microscope (RT-SHPM) was used for real-time imaging of surface magnetic domains of floppy disks, Sr ferrite magnets and Bi-substituted iron garnets placed in large external bias fields. Domain wall nucleation was observed in the garnets where bubble lattices expanded, collapsed and transformed into stripe domains in cyclic bias fields. Evolution of RT-SHPM images was compared with conventional vibrating sample magnetometer measurements.

Magnetic force microscopy study of La 0.7Sr 0.3MnO 3/Si(0 0 1) around its Curie temperature

A transform of the surface magnetic domain patterns of a 350-nm-thick LSMO thin film at Curie temperature ( T c, 340 K) was first observed by magnetic force microscopy (MFM) at its remanent state. This result is in good agreement with that of the SQUID measurements; the in-plane magnetization of this thin film declined with an increase in temperature and the T c was measured at 340 K. Therefore, the in situ MFM domain study is found to be a useful tool for thermo-magnetic behavior for thin films of this kind.

Spin polarized Auger electron spectroscopy of Fe and Ni

Surface sensitive experiments, in which the spin-polarized electrons are involved, play an important role for magnetic characterization, since the spin-polarized electrons are fingerprints for the local magnetization. Scanning electron microscope with polarization analysis (SEMPA) is one of the most powerful tools to investigate the surface magnetic domain structure of magnetic materials. On the other hand, at energies high enough to generate a two-hole final state arising from Auger transitions, it is possible to observe the spin polarization of the Auger electrons. These electrons reveal element-specific local magnetic information, particularly valuable for surface magnetic studies with composite systems. By using the uniqueness of the UTA-SEMPA tool, one can obtain the magnetic domain picture and also perform spin-polarized Auger electron spectroscopy studies by probing a single domain at the surface. In this study, precisely knowing the probed domain, spin polarization of electrons from super Coster–Kronig MMM Auger emissions on Fe and Ni samples have been investigated. The polarization enhancement above the 3p(M23) threshold is observed on both samples.

Effect of magnetic annealing on magnetization changes of amorphous ribbon under stress

The effect of magnetic heat treatment on the stress-magnetization properties of Co-based amorphous ribbon with negative magentostriction constant was investigated. The sample changes the sign of its magnetostriction constant from negative to positive value due to the heat treatment under perpendicular and normal direction of magnetic field. The surface magnetic domain configurations were observed to reveal the mechanism of this magnetization change. The abnormal magnetization change under tensile stress is deeply connected with the appearance of complicated domain configurations.

Magnetization distribution of 180° domain walls at the surface of 3% Si–Fe sheets

The surface magnetic domain structure of 100μm thick 3% Si–Fe sheets was imaged by using a scanning electron microscope with polarization analysis (SEMPA) in ultra-high vacuum. Two orthogonal in-plane components of the secondary electron spin polarization were measured to obtain the surface magnetic microstructure. Using a calibration sample, we have determined that our spatial resolution varies between 150 and 250nm depending on the experimental conditions. The 3% Si–Fe sheets have undergone tertiary recrystallization and have uniaxial anisotropy. At the center, the samples are composed of 180° stripe domains ((110) texture). High-magnification SEMPA images show that the magnitude of the in-plane magnetization vanishes at the domain walls. The width of the observed domain walls is approximately 400nm on the same samples. In order to confirm that the magnetization is out-of-plane in the domain walls, SEMPA measurements were performed with the sample tilted around the horizontal axis. It was observed that the out-of-plane component of the magnetization is projected onto the sample plane. With increasing tilt angle, line scans taken from corresponding SEMPA images clearly show that the in-plane component of magnetization at the domain walls increases. This is the first observation of out-of-plane magnetization at a surface domain wall.