Magnetic Domain Size Research Articles

Paleomagnetism and tectonics from the late Pliocene to late Pleistocene in the Xalapa monogenetic volcanic field, Veracruz, Mexico

AbstractThe Xalapa monogenetic volcanic field, Veracruz, Mexico is located at the eastern end of the Trans-Mexican Volcanic Belt. This study uses specimens from 0.8 ka to 5.96 ± 0.156 Ma Xalapa lava deposits and from 4.5 ± 0.028 Ma La Concha ignimbrite. The study identifies the magnetic mineralogy by reflected light microscopy, thermomagnetic curves, and coercivity estimates. It further defines the magnetic domain size distribution by hysteresis plots, Day diagrams, and first-order-reversal-curves. Characteristic remanent directions and virtual geomagnetic poles are also calculated. The characteristic remanent directions are used to establish the magnetostratigraphy and to identify the net rotation experienced, at each site, since the emplacement. The results allow the identification of the rotation domains, and R′-, P-, and Y-shears, active since the past ∼2.5 m.y. in the region and a better characterization of the displacement along the Río Actopan fault, active in the Xalapa monogenetic volcanic field.

Микромагнитные и магнитооптические свойства пленочных структур вида ферромагнетик/тяжелый металл

The paper presents a comparative analysis of the magnetic properties of thin films of CoPt, CoPd, FePd alloys. The films were fabricated by electron-beam evaporation, with the variation of a ferromagnetic material content. Studies of the micromagnetic structure showed a decrease in the size of magnetic domains with an increase of the Co content in CoPt and CoPd films, which is associated with the presence of two magnetic phases in the films. Magneto-optical studies have shown abnormally high Faraday angles and the absence of the Kerr effect for CoPt films, which makes them attractive for practical applications in optics. The minimum coercive field values in magnetic field dependences of magnetization, as compared with other films, were obtained for FePd films, which is also associated with the peculiarities of the magnetic structure.

Hard Magnetic Property Improvement of Melt-Spun PrCo5 Ribbons by Fe and C Doping

Magnetic properties and microstructure of melt-spun PrCo5− x − y Fe x C y ( x = 0 and 0.3; y = 0–0.3) ribbons are studied. For PrCo5 ribbons spun at lower wheel speed of 20 m/s, the coexistence of 2:17 phase with magnetic hard 1:5 phase leads to low coercivity of 0.6 kOe. Increasing wheel speed to 40 m/s imroves the coercivity to 3.3 kOe due to the increased volume fraction of 1:5 phase. Interestingly, magnetic properties of PrCo5 ribbons melt spun at 40 m/s ( Br = 6.4 kG, i H c = 3.3 kOe, and ( BH )max = 4.5 MGOe) are improved to Br = 6.1–6.5 kG, i H c = 7.8–13.5 kOe, ( BH )max = 7.3–8.9 MGOe by doping C, and significantly enhanced to Br = 6.3 kG, i H c = 16.1 kOe, and ( BH )max = 9.3 MGOe for C and Fe co-doped PrCo4.6Fe0.3C0.1 ribbons. The structural and thermo-magnetic analysis confirms that the entrance of Fe and part of C into the crystal structure of 1:5 phase leads to the increase of Curie temperature. Doping proper C content not only uniformly refines grain size and, therefore, improves the squareness of demagnetization curve and ( BH )max, but also increases the volume fraction of 1:5 phase, and thus enhances the coercivity. The increased volume fraction of 1:5 phase and the reduced magnetic domain size due to refined microstructure by co-doping Fe and C make PrCo4.6Fe0.3C0.1 ribbons exhibit a high permanent magnetic performance. They are promising candidate materials for making bonded magnets.

Magnetic order and disorder in nanomagnets probed by superconducting vortices

We have studied two nanomagnet systems with strong (Co/Pd multilayers) and weak (NdCo alloy films) stray magnetic fields by probing the out-of-plane magnetic states with superconducting vortices. The hybrid samples are made of array of nanomagnets embedded in superconducting Nb thin films. The vortex motion detects relevant magnetic state features, since superconducting vortices are able to discriminate between different magnetic stray field strengths and directions. The usual matching effect between the superconducting vortex lattice and the periodic pinning array can be quenched by means of disorder magnetic potentials with strong stray fields at random. Ordered stray fields retrieve the matching effect and yield asymmetry and shift in the vortex dissipation signal. Furthermore vortices can discriminate the sizes of the nanomagnet magnetic domains, detecting magnetic domain sizes as small as 70 nm. In addition, we observe that the vortex cores play the crucial role instead of the supercurrents around the vortex.

Research of Rolling Process with Warm for Cold-Rolled Non-Oriented Electrical Steel

The rolling process with warm for cold-rolled non-oriented electrical steel in pickling and rolling and continuous annealing was studied. Research shows when feeding the hot plate for Pickling and rolling mill in 100~120°C, pickling steel is almost no temperature rise, with the temperature of hot rolled silicon steel pickling effect is good, the cleaning rate reaches 100%; the steel sheet is stable running in looper for the strip temperature softening effect and shape of rolled strip is good, deviation below 8μm. Cold rolled plate feeding in 60~80°C for continuous annealing unit, the plate is almost no heating in Alkaline wash. Alkaline wash effect is good for the cold rolled plate with temperature steel, plate surface defect can be significantly reduced and wash rate is up to 100%; steel plate with temperature is not deviation in continuous annealing looper for softening. In addition, organization, texture, the second particles and magnetic energy also were studied. It was found that the steel sheets’ microstructure is uniform after cold rolling, the grain is evenly stretched; belt warm rolling and the grain orientation of the cold-rolled sheet steel texture is obviously, which formed two main categories with {111} <uvw> and {hkl} <110> texture; after annealing, the second particles MnS and AlN particles has been roughened and close to the magnetic domain size, which reduce the obstacle second phase particles on the magnetic domains; Compared with the conventional process, the iron loss decreased slightly, magnetic induction increased slightly.

Thermoremanent Behavior in Synthetic Samples Containing Natural Oxyexsolved Titanomagnetite

AbstractUnderstanding Earth's geodynamo provides us a window into the evolution of the Earth's core, which requires accurate data about how its strength varies with time. Classic Thellier‐style paleointensity experiments assume that studied specimens contain only noninteracting single‐domain (SD) magnetic particles. Interacting grains commonly occur in volcanic rocks but are generally assumed to behave like equivalently sized SD grains. Multidomain (MD) grains can cause erroneous PI estimates or cause Thellier‐style experiments to fail entirely. Synthetic specimens containing naturally formed magnetite with MD grains and oxyexsolved titanomagnetite (closely packed SD grains) were subjected to various partial thermoremanent magnetization (pTRM) experiments, which tested nonideal behavior as a function of pTRM acquisition and loss inequality, thermal history, and repeated heating steps. For all grain sizes and domain states, pTRMc (heating and cooling in a nonzero field) gives larger values, compared to pTRMb (heating in a zero field and cooling in a nonzero field), by ∼5.5%. Oxyexsolved grains appear prone to the same concave‐up, nonideal Arai plots commonly observed in MD specimens, which also has potential implications for the multiple‐specimen, domain‐state corrected protocol. Repeated heatings cause additive deviations from ideality with relatively small impacts on Arai plot curvature for both grain types. Experiments with higher initial demagnetization temperatures had lower curvatures, with the most SD‐like behavior occurring in the uppermost 20 C of the (un)blocking temperature range. Samples containing mixtures of magnetic domain sizes are likely to behave less ideally at lower temperatures but become more ideal with increasing temperature as the nonideal grains unblock.

Effect of Al content on magnetic domains of {1 0 0} grains in electrical steels

Magnetic domains of {100} grains in electrical steels with 1.85 ≤ Al ≤ 6.54 wt% were observed by magneto-optic Kerr microscopy. The characteristics and motion of magnetic domains were correlated with hysteresis loss, anomalous loss and permeability. As Al contents increased, domain wall energy decreased, so the magnetic domain size of {100} grains decreased. In steel with Al 6.54 wt%, 90° domain walls appeared, so the complexity of domain structures increased. Addition of Al caused increase in hysteresis loss. Anomalous loss decreased until Al 4.68 wt%, then saturated, despite high resistivity and small domain size. External magnetizing force H→ required to induce maximum permeability µmax increased drastically at Al 6.54 wt%. These changes of magnetic properties may be caused by pinning of 90° walls during magnetization. As domain size decreased to form closure domains, the complexity of reorganization of magnetic domains increased, and they were interrupted by pinning 90° walls.

Suppression of all-optical switching in He+ -irradiated Co/Pt multilayers: influence of the domain-wall energy

The observation of all-optical helicity-dependent switching (AO-HDS) in ferri- and ferro-magnetic materials depends not only on the saturation magnetization, but on the magnetic domain size which takes into account the competition between the demagnetizing energy and the domain wall (DW) energy. In this paper, we study the optical response of Co/Pt multilayers for which perpendicular magnetic anisotropy can be tuned using He+ -irradiation. This allows us to correlate the observation of AO-HDS with the magnetic properties of the He+ -irradiated multilayer. These results give direct evidence of the crucial role of the DW energy in the laser-induced switching process.

Postshock Thermally Induced Transformations in Experimentally Shocked Magnetite

AbstractWe studied the effect of 973 K heating in argon atmosphere on the magnetic and structural properties of a magnetite‐bearing ore, which was previously exposed to laboratory shock waves between 5 and 30 GPa. For this purpose magnetic properties were studied using temperature‐dependent magnetic susceptibility, magnetic hysteresis and low‐temperature saturation isothermal remanent magnetization. Structural properties of magnetite were analyzed using X‐ray diffraction, high‐resolution scanning electron microscopy and synchrotron‐assisted X‐ray absorption spectroscopy. The shock‐induced changes include magnetic domain size reduction due to brittle and ductile deformation features and an increase in Verwey transition temperature due to lattice distortion. After heating, the crystal lattice is relaxed and apparent crystallite size is increased suggesting a recovery of lattice defects documented by a mosaic recrystallization texture. The structural changes correlate with modifications in magnetic domain state recorded by temperature‐dependent magnetic susceptibility, hysteresis properties and low‐temperature saturation isothermal remanent magnetization. These alterations in both, magnetic and structural properties of magnetite can be used to assess impact‐related magnetic anomalies in impact structures with a high temperature overprint.

Nanoscale control of perpendicular magnetic anisotropy, coercive force and domain structure in ultrathin Ru/Co/W/Ru films

Development of fast and energy-efficient spintronic devices requires novel nanoscaled materials with controllable magnetic properties. Here we show that the introduction of an ultrathin W interlayer between Co and Ru in Ru/Co/Ru films enables to preserve perpendicular magnetic anisotropy (PMA) and dramatically reduce the coercive force and size of magnetic domains. We find that the Ru/Co/W/Ru films with up to 0.35 nm of the nominal thickness of W have robust PMA. The observed formation of a dendritic domain structure with small domains having homochiral Néel domain walls is an indicator of the interfacial Dzyaloshinskii-Moriya interaction appearing in trilayers with asymmetrical interfaces. The inversion-symmetry-broken Ru/Co/W/Ru films are a potential host for nucleation and manipulation of non-trivial spin textures like chiral domain walls and skyrmions.

Synthesis and characterization of cobalt ferrite nanoparticles prepared by the glycine-nitrate process

In this research, microstructural evolution and magnetic properties of cobalt ferrite spinel (CoFe2O4) were studied. The ferrite was prepared by the glycine-nitrate process (GNP) followed by calcination process, and subsequent high energy mechanical milling. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and vibration sample magnetometery (VSM) methods. The results showed that the desired high purity spinel phase was formed through a complete combustion reaction using the G/N ratio of 1.48. The as-synthesized powder revealed the coercivity and saturation magnetization of 900 Oe and 62.83 emu/g, respectively. The CoFe2O4 phase was stable after calcination at 500 °C for 2 h under argon atmosphere and subsequent milling processes for 2 and 4 h. The highest coercivity value was obtained for the calcined sample (975 Oe), whose average particle size exhibited noticeable conformity with the single magnetic domain size of CoFe2O4 (~ 40 nm). For the 2 h-milled and 4 h-milled samples, the average particle size was below the single magnetic domain size, causing a significant reduction in coercivity values (820 and 770 Oe, respectively). The saturation magnetization was increased negligibly after the calcination process (63.22 emu/g), while it was raised to 71.47 and 73.98 emu/g after 2 and 4 h milling, probably due to the cationic redistribution during milling.

Tailoring magnetic domains in Gd-Fe thin films

This paper presents the global modification of magnetic domains and magnetic properties in amorphous Gd19Fe81 thin films with rapid thermal processing at two distinct temperatures (250oC and 450oC), and with different time intervals viz., 2, 5, 10 and 20 minutes. 100 nm thick as-prepared films display nano-scale meandering stripe domains with high magnetic phase contrast which is the signature of perpendicular magnetic anisotropy. The films processed at 250oC for various time intervals show successive reduction in magnetic phase contrast and domain size. The domain pattern completely disappeared, and topography dominated mixed magnetic phase has been obtained for the films processed at 450oC for time intervals greater than 2 minutes. The magnetization measurements indicate the reduction in perpendicular magnetic anisotropy with increase in saturation magnetization for all the rapid thermal processed films. The experimental outputs have been used to simulate the domain pattern. Reduction in uniaxial anisotropy along with the increase in saturation magnetization successfully explain the experimental trend of decrease in domain size and magnetic contrast.

Experimental heat capacities, excess entropies, and magnetic properties of bulk and nano Fe3O4-Co3O4 and Fe3O4-Mn3O4 spinel solid solutions

We have measured the heat capacities of several well-characterized bulk and nanophase Fe3O4-Co3O4 and Fe3O4-Mn3O4 spinel solid solution samples from which magnetic properties of transitions and third-law entropies have been determined. The magnetic transitions show several features common to effects of particle and magnetic domain sizes. From the standard molar entropies, excess entropies of mixing have been generated for these solid solutions and compared with configurational entropies determined previously by assuming appropriate cation and valence distributions. The vibrational and magnetic excess entropies for bulk materials are comparable in magnitude to the respective configurational entropies indicating that excess entropies of mixing must be included when analyzing entropies of mixing. The excess entropies for nanophase materials are even larger than the configurational entropies. Changes in valence, cation distribution, bonding and microstructure between the mixing ions are the likely sources of the positive excess entropies of mixing.

Heat Treatment Effect on Magnetic Microstructure of Fe73.9Cu1Nb3Si13.2B8.9 Thin Films

Fe73.9Cu1Nb3Si13.2B8.9 (Finemet) thin films were deposited on the glass substrates by means of radio frequency sputtering. The films thickness was varied from 10 to 200 nm. Heat treatment at temperatures of 350, 400 and 450 °C were performed for 30 minutes in order to control thin film structural state. The X-ray powder diffractometry revealed that the crystallization of α-FeSi nanograins took place only at 450 °C whilst the other samples stayed in the amorphous state. Relation between the structure and magnetic properties of the films was discussed in the framework of random magnetic anisotropy model and the concept of stochastic magnetic domains. The latter was investigated using magnetic force microscopy (MFM). MFM data showed formation of such magnetic domains only in samples thermally treated at 450 °C. There was a tendency of the magnetic domain size reduction with the thickness decrease.

Single shot all optical switching of intrinsic micron size magnetic domains of a Pt/Co/Pt ferromagnetic stack

We demonstrate that magnetization reversal in a ferromagnetic Pt/Co/Pt stack can be induced by a single femtosecond laser pulse. We find that the size of the switched spot is comparable to the size of the intrinsic magnetic domains. It requires an absorbed energy density of ∼4 mJ cm−2, beyond which the excited spot fragments into a multidomain structure. The switching process can be toggled with sequential laser pulses and is helicity-independent. Furthermore, the dynamics of the magnetization reversal occurs in a timescale less than one microsecond. These results suggest that all-optical switching in ferromagnetic films requires that the laser spot matches with the specific domain sizes.

Magnetic Mineralogical Variability along Deccan Trap Basalt Borehole (KBH07), Koyna Deep Continental Drilling Program, Western Maharashtra, India

ABSTRACT A 1248 m long core (KBH 07, 17°18'07" N; 73°47'28.2"E, 960m above msl) drilled up to basement in the Deccan traps from Koyna region was sampled at ∼10m interval for magnetic mineralogical studies. Analysis of routine rock magnetic parameters (mass specific magnetic susceptibility: χlf, frequency dependence of susceptibility: χfd, susceptibility of anhysteretic remanance: χARM, saturation isothermal remanance: SIRM, remanance coercivty: B(0)CR, SoftIRM, HardIRM, S-Ratio, SIRM/χlf, χARM/χlf) and density (σ, gm/ cc) depicted significant higher order temporal variation. The χlf varies between 13 and 309 x 10−8m3/kg and is independent of density variation. The χARM, B(0)CR and S-Ratios indicate majority of SD-PSD ferrimagnets with episodes of MD ferrimagnetic concentration and few hard coercivity components. The giant plagioclase lath bearing (GPB) horizons show highest variability of ferrimagnetic concentration marked by anomalous peaks. Overall the variability of rock magnetic parameters independent of lava flow units suggest that the changeover in magnetic mineral concentration, composition and domain size occur at major episodes in magma composition (e.g., primary source, crustal contamination and fractional crystallization). The studied parameters are therefore examined to mark intervals of (i) magma compositional changes, (ii) zones of oxidative conditions and (iii) rapid/slow cooling intervals demanding detailed petrologic studies. We identified one I order trend, four II order cycles and eight III order cycles for the purpose of correlation. Notable peak in χlf at 650-700m, the changeover in rock magnetic parameters at ∼930 m and ∼280 m can facilitate marker intervals while several higher order variations can be adopted for high resolution correlation to other boreholes in the region. The complex variation in rock magnetic parameters independent of flow units reflect temporal magnitudes of compositional variability, cooling and emplacement history that needs detailed petro-mineralogical attempts; and the present data is useful for high order inter-core correlations under the deep drilling program.

Programmable magnetic domain evolution in magnetic auxetic systems

In this work, we investigate the evolution of magnetic domains with time in magnetic auxetic systems using the Ising model. We show that the mechanical deformation of the structure affects the way how domains evolve and that their rate of growth does not follow a well‐known power law associated with the Ising model for systems corresponding to a specific distance between Ising spins. We also show that the variation in the rate of deformation of the system leads to completely different results in terms of the change in size of magnetic domains and domain energy. This means that upon changing the speed used to deform the system, it is possible to control the growth of magnetic domains and hence control the magnetic properties of the whole system. This may prove to be very important in the case of potential applications such as magnetic freezers where the magnetocaloric effect resulting with a change in temperature could be affected by the rate of deformation of the discussed auxetic structure.

Optical, magnetic and thermal properties of colloidal suspension of ferrofluids synthesized by laser ablation

A high power Nd: YAG laser has been employed to produce magnetic colloids (ferrofluids) of iron oxide nanoparticles (NPs) in double distilled water. It is found that FeO (Wüstite) phase of iron oxide has been produced as an initial product; after oxidation and agglomeration it appears as Fe2O3 a stable composition of iron oxide. UV–visible absorption spectroscopy has been employed to distinguish both phases of iron oxide NPs. Absorption band gap of as synthesized ferrofluids at different pulse energies (30, 40, 50, 60 mJ) has been calculated. The absorption band gap of as synthesized FeO magnetic colloids is found in the range of (2.91–3.13 eV) and (3.37–3.91 eV) respectively which arises due to pair excitation and charge transfer. Absorption band gaps of Fe2O3 are found in the range of (2.16–2.28 eV) and (2.68–3.10 eV) respectively again due to pair excitation and charge transfer. Magnetic measurement was performed using VSM which confirms antiferromagnetic nature of FeO NPs with coercivity 47 Oe and magnetic domain size 73.50 Å at 300 K. Zero field cooled and field cooled magnetization confirms blocking and Néel temperature 245 ± 2 K and 181 ± 2 K respectively.Highlight for review1. As synthesized colloidal suspension of iron oxide NPs can be used as efficient cooling agent.2. FeO composition of iron oxide has been synthesized using PLA3. Optical band gap of colloidal suspension of iron oxide NPs is calculated at different laser energy.4. Magnetic properties of iron oxide NPs have been studied.

Controlling the Topological Sector of Magnetic Solitons in Exfoliated Cr_{1/3}NbS_{2} Crystals.

We investigate manifestations of topological order in monoaxial helimagnet Cr_{1/3}NbS_{2} by performing transport measurements on ultrathin crystals. Upon sweeping the magnetic field perpendicularly to the helical axis, crystals thicker than one helix pitch (48nm) but much thinner than the magnetic domain size (∼1 μm) are found to exhibit sharp and hysteretic resistance jumps. We show that these phenomena originate from transitions between topological sectors with a different number of magnetic solitons. This is confirmed by measurements on crystals thinner than 48nm-in which the topological sector cannot change-that do not exhibit any jump or hysteresis. Our results show the ability to deterministically control the topological sector of finite-size Cr_{1/3}NbS_{2} and to detect intersector transitions by transport measurements.

Domain engineering of the metastable domains in the 4f-uniaxial-ferromagnet CeRu2Ga2B

In search of novel, improved materials for magnetic data storage and spintronic devices, compounds that allow a tailoring of magnetic domain shapes and sizes are essential. Good candidates are materials with intrinsic anisotropies or competing interactions, as they are prone to host various domain phases that can be easily and precisely selected by external tuning parameters such as temperature and magnetic field. Here, we utilize vector magnetic fields to visualize directly the magnetic anisotropy in the uniaxial ferromagnet CeRu2Ga2B. We demonstrate a feasible control both globally and locally of domain shapes and sizes by the external field as well as a smooth transition from single stripe to bubble domains, which opens the door to future applications based on magnetic domain tailoring.