Surface Hysteresis Loops Research Articles

Heating influence on magnetic structure in Co and Fe rich amorphous microwires

The influence of temperature on surface magnetic structure has been studied in Co- and Fe-rich magnetic glass covered microwires. The investigations have been performed using magneto-optical Kerr effect technique with a thermo-controlled system. It was found different types of domain structures depending on the temperature and the microwire composition. These types are characterised by the different domain period and the angle of the inclination of domain walls. It was established the direct correlation between surface domain structures and hysteresis loops. The coexistence of domain walls with different value of mobility has been found. It was observed original mechanism of the domain structure transformation: sharp change in the domain structure without movement of the domain walls.

Influence of Tensile Stress on the Surface Magneto-Optical Hysteresis Loops in Amorphous and (Nano)Crystalline Ribbons

The behavior of the surface magnetic anisotropy in the amorphous and (nano)crystalline ribbons is investigated using the magneto-optical (MO) methods. In this paper, the differential intensity MO method is extended by the specially designed sample holder suitable for applying the tensile stress in the ribbon axis. Measured surface hysteresis loops, represented as a function of tensile stress <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$\sigma$ </tex-math></inline-formula> , offer an interesting insight into the magnetoelastic properties of the ribbon surface phases. These dependencies are studied and discussed in the case of the surface-crystallized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">${\rm Co}_{66}{\rm Fe}_{4}{\rm Si}_{15}{\rm B}_{15}$ </tex-math></inline-formula> and the as-quenched amorphous <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">${\rm Fe}_{77.5}{\rm Si}_{7.5}{\rm B}_{15}$ </tex-math></inline-formula> ribbons. It is shown that the response of the surface crystalline phases and the amorphous matrix on applied stress is significantly different. This is manifested by the changes in the value and sign of magnetostriction coefficient <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$\lambda_{s}$ </tex-math></inline-formula> . Good agreement between the surface and bulk magnetostriction is obtained for the FeSiB ribbons that are amorphous in the volume as well as on the surface.

Order parameters and hysteresis behavior of a ferromagnetic Blume–Capel thin film: The role of the crystal field interactions

As a complementary work of a recent study (Physica B 433 (2014) 96), ferromagnetic thin films in simple cubic lattice structure described by a spin-1 Blume–Capel Hamiltonian have been considered within the framework of effective-field theory (EFT). Thermal variations of bulk and surface order parameters (i.e. magnetization and quadrupolar moments), as well as hysteresis loops in the presence of modified surface interactions, and crystal fields have been examined. We have found that depending on the type of the phase transition (i.e. ordinary or extraordinary), bulk and surface order parameters may exhibit fairly non-monotonous and quite exotic profiles. Regarding the bulk and surface hysteresis loops, at a fixed set of system parameters, both the bulk and surface hysteresis loops exhibit the same coercivity whereas remanence of a bulk (surface) loop is greater than that of a surface (bulk) loop in ordinary (extraordinary) case.

Full-scale magnetic, microstructural, and physical properties of bilayered CoSiB/FeSiB ribbons

The paper is devoted to the detailed analysis of microstructural and magnetic properties of the as-quenched bilayered Co72.5Si12.5B15/Fe77.5Si7.5B15 ribbons prepared by the planar flow casting (PFC) method with single crucible. The interface between both amorphous Co- and Fe-based layers is not uniform and its thickness ranges from 0.5 to 6μm over the whole ribbon length. Dependences of mechanical characteristics on the ribbon thickness show increase in Young’s modulus from 140 to 170GPa and decrease in microhardness from 18 to 13GPa, when measured from the wheel (Co) to air (Fe) side. By fixing the coiled ribbon on the planar sample holder a uniaxial magnetic anisotropy with the out-of-plane and the in-plane easy axis is induced on the air and wheel side, respectively. Bulk magnetic properties confirm that perpendicular anisotropy observed on the air side becomes stronger as getting deeper under the surface and overlaps the in-plane anisotropy from the wheel side. This is in good agreement with Mössbauer measurements. Magnetic characteristics (surface hysteresis loops and domains, bulk hysteresis loops and thermomagnetic curves) of the bilayered samples were further compared with the single-layered CoSiB and FeSiB alloys.

Magnetic properties of sub-micrometric Fe-rich wires

The investigation of the magnetization reversal has been performed in Fe-rich sub-micrometric glass covered wires of different radiuses. The surface magnetization reversal has been studied using the magneto-optical Kerr effect. The axial tensile stress and torsion stress have been applied during the experiments.Surface hysteresis loop was found to be rectangular because of magnetic bistability. This confirms the existence of the Surface Large Barkhausen Jump in sub-micrometric glass covered wires explained by the magnetization reversal in a large single surface domain.The analysis of the tensile and torsion stresses' transformation of surface hysteresis loop proves that magnetic bistability earlier observed in thicker glass covered microwires exists down to one order decrease of wire's diameter.

Rapidly solidified amorphous nanowires

Results on the preparation and magnetic characterization of rapidly solidified amorphous glass-coated nanowires are reported. Rapidly solidified nanowires have been investigated by means of bulk and surface hysteresis loop measurements, scanning electron microscopy, and ferromagnetic resonance. Domain wall velocity has been measured to demonstrate the suitability of the new nanowires for spintronic applications. Changes in composition, in the thickness of the glass coating, and nanowire dimensions allow extensive tailoring of the domain wall mobility.

Magnetic behavior and domain structure in as-quenched, annealed, and stress-annealed CoFeCrSiB ribbons

Combination of magneto-optical (MO) vector magnetometry and magneto-optical Kerr microscopy is used to investigate the surface magnetic properties of amorphous CoFeCrSiB ribbons. Strongly inhomogeneous magnetic behavior of ribbons in as-quenched state is improved by field-annealing and stress-annealing processes that induce weak uniaxial longitudinal and transverse anisotropy. It was shown that values of coercive and anisotropy field increase with increasing annealing temperature. Inclination of easy axis from the ribbon axis is estimated by comparing the measured surface hysteresis loops with the Stoner–Wohlfarth model, and is supported also by the Kerr microscopy. Method with the current flowing through the ribbon is proposed for magnetic domains observations.

Optimal growth windows of multiferroic BiFeO 3 films and characteristics of ferroelectric domain structures

Multiferroic BiFeO 3 films of smooth surface and fully-saturated ferroelectric hysteresis loops have been grown by RF magnetron sputtering. The (001)-oriented epitaxial films showed a large remanent polarisation of 61 µC/cm 2. A strategy to grow BiFeO 3 films of good ferroelectric property was demonstrated, that was using fast growth rate to achieve accurate stoichiometry for the BiFeO 3 phase and at the same time to avoid the formation of impurity phases associated with the fast growth by accurate control of thermodynamic parameters such as oxygen partial pressure and temperature, as well as proper selection of substrates. Piezoresponse force microscopy revealed fine spontaneous domains for highly resistive epitaxial films, which were switchable under DC biases. For the polycrystalline films of increased density of free carriers, single-domain grains of about 200 nm in diameter were observed due to effective compensation of depolarisation field by free carriers and therefore allowing larger domains.

Outer shell structure in nearly zero magnetostrictive amorphous microwires

Nearly zero magnetostrictive microwires have been proven to be very versatile, due to their extremely soft magnetic properties, the changes in their magnetization mechanism with dimensions, and the appearance of sensitive application-related effects, such as the large Barkhausen and the giant magnetoimpedance effects. Their sensitive magnetoimpedance response originates in the specific domain structure, composed of an inner core and an outer shell (OS), since the OS with a circumferential easy axis is the main region involved in the magnetoimpedance effect. The circumferential OS is believed to display a bamboolike structure with consecutive rings circumferentially magnetized in opposite directions. However, earlier theoretical studies predicted a uniformly magnetized OS as being energetically favored. This paper aims to clarify this contradiction. The variation of the magnetostatic energy from the bamboo domain to the uniformly magnetized state has been calculated and it has been found to be null. Therefore, a uniformly magnetized OS has lower energy due to the absence of domain walls. Calculation results are supported by magneto-optical Kerr effect surface domain images and surface hysteresis loops. For large values of the metallic nucleus diameter, as well as for microwires with the glass coating removed, the OS vanishes, being replaced with a surface region with helical magnetization, which expands toward the microwire surface.

Surface and bulk magnetic properties of amorphous and nanocrystalline Ni-substituted FINEMET samples

Abstract The effect of partial substitution of Fe by Ni on the bulk and surface magnetic properties in as-quenched and nanocrystalline Fe 73.5− x Ni x Cu 1 Nb 3 Si 13.5 ( x = 0, 8, 10 and 20) alloys has been investigated. A study of the variation of the surface magnetic properties with oxidation in these alloys is also presented. The surface hysteresis loops were obtained by the transverse magneto-optical Kerr effect. The experimental results show that the as-quenched and annealed samples with lower surface coercive field values are those with lower Fe/Si ratio in the sample surfaces. No significant changes between the values of surface H c for the oxidized and non-oxidized annealed samples with the same Ni content have been observed.

Depth-sensitive characterization of surface magnetic properties of as-quenched FeNbB ribbons

The longitudinal magneto-optical Kerr effect (MOKE) is used to study the surface magnetic properties of as-quenched FeNbB ribbons. MOKE surface hysteresis loops measured from both ribbon sides confirm different magnetic behavior. Wheel ribbon side shows heterogeneous (crystalline/amorphous) properties, thickness of crystalline phase (about 3 nm) was established by comparing the measured magneto-optical angles of Kerr rotation and ellipticity at different incident angles with the theoretical model. Effective crystalline phase observed at shiny ribbon side is harder (coercive field about 40 Oe) than that on wheel side and penetrates deeper into the material volume. Its thickness 1.3 μ m estimated from the weight reduction of the ribbon during surface etching is in good agreement with cross-section image obtained using the scanning electron microscopy (SEM). The sources of magnetoelastic anisotropy were identified in the bulk as well as on the ribbon surface using the magneto-optical Kerr microscopy.

Structural and Magnetic Behaviour of Soft Magnetic Finemet-Type Ribbons

Different kinds of magnetic anisotropies have been induced during the nanocrystallization process of Co- and Ni-rich amorphous ferromagnetic (Finemet) ribbons by the application of a constant stress or an axial magnetic field during the annealing process. Magnetization measurements have evidenced the presence od macroscopic anisotropy in the treated samples. The main goal of this work has been, after a careful DSC study, the structural analysis of the treated ribbons using X-ray Diffraction and Atomic Force Microscopy (AFM), detecting substantial differences in the crystallization state and grain size of the samples depending on the thermal treatment that was carried out. Moreover, AFM measurements revealed in all the treated samples a strong nanocrystallisation of the surface without evidences of amorphous matrix, which contrast with XRD measurements that have shown a high content of amorphous phase in the bulk of the ribbons. Magneto-optical Kerr effect measurements have been performed with the aim to elucidate the complex magnetic behaviour that is expected for the surface of the ribbons, measuring surface hysteresis loops that showed much higher coercive field values than that obtained in the bulk material.

Relation between surface magnetization reversal and magnetoimpedance in Co-rich amorphous microwires

We report the investigations on the giant magnetoimpedance (GMI) effect and the surface magnetic structure performed in the series of glass covered Co-rich amorphous microwires with different thicknesses of glass covering. The calculation of the surface hysteresis loops has been performed in the frames of the model which takes into account the helical magnetic anisotropy. The correlation between the value of the GMI ratio, the jump of the circular magnetization, and the value of the angle of helical anisotropy has been established. It was found that the angle of the surface helical anisotropy, for which the highest value of GMI, is close to 60°.

Magnetic behavior and microstructure of Finemet-type ribbons in both, surface and bulk

Different kinds of magnetic anisotropies have been induced during the nanocrystallization process of Co- and Ni-rich amorphous ferromagnetic (Finemet) ribbons using diverse procedures like the application of a constant stress or an axial magnetic field during the annealing process. Magnetization measurements have evidenced the anisotropy of the treated samples. The main goal of this work has been the structural and microstructural analysis of the treated ribbons using X-ray Diffraction (XRD) and Atomic Force Microscopy (AFM), detecting substantial differences in the crystallization state and grain size of the samples depending on the treatment that was carried out. Moreover, AFM measurements revealed in all the treated samples a strong nanocrystallization of the surface without evidences of amorphous matrix, which contrast with XRD measurements that have shown a high content of amorphous phase in the bulk of the ribbons. Magneto-optical Kerr effect measurements have been performed with the aim to elucidate the complex magnetic behavior that is expected for the surface of the ribbons, measuring surface hysteresis loops that show much higher coercive field values than in the bulk.

Surface and Bulk Magnetic Hysteresis Loops of Co-Rich Glass Covered Microwires

The magnetization reversal process in the surface and volume areas of Co-rich glass covered microwires has been investigated. The value of the helical anisotropy has been determined in two wires with different thickness of glass covering. The dependence of the coercive field on the frequency of the external axial magnetic field was studied in the surface and volume of the microwires

The magnetic characteristics of perpendicular magnetic tunnel junction with MgO and Al–O oxidation layers in various thickness

In this work we show the magnetic characteristics of perpendicular magnetic tunnel junction (pMTJ) with different oxidation layers. The pMTJs structures were made by RF and DC magnetron sputtering. Individual depositions of magnesium oxide layers and of aluminum oxide films were prepared by plasma oxidation. The experimental results showed that the initial switching field was decreased as the magnesium oxide thickness was increased. Further work of the aluminum oxide surface roughness and hysteresis loop influenced by different oxidation layers on pMTJs structures will be discussed as well.

Two magnetic phases in cold-drawn Fe-rich amorphous wire

Magnetic properties have been studied in ferromagnetic amorphous wires of nominal composition Fe 77.5B 15Si 7.5 and diameter 0.05 mm prepared by cold-drawing technique. Conventional and surface hysteresis loops were measured by fluxmetric method and by magneto-optical Kerr effect method, respectively. Saturation magnetization dependence with the current density has been obtained. Two Curie points were clearly distinguishable on this dependence that could be associated with the existence of two ferromagnetic phases. On the other hand, two successive jumps of magnetization have been observed in fluxmetric as well as in magneto-optical curves. The joint analysis of the bulk and surface hysteresis loops permits us to conclude that the cold-drawing post process induces strong helical anisotropy in the Fe-rich wires studied. The helical magnetic structure exists in the surface and, also, in the volume of the wire. We consider that the helical magnetic structure forms the separate magnetic phase that finds the reflection in the two Curie points behavior.

Optimization of giant magnetoimpedance in Co-rich amorphous microwires

The dependences of the magnetoimpedance ratio /spl Delta/Z/Z of soft magnetic Co/sub 67/Fe/sub 3.85/Ni/sub 1.45/B/sub 11.5/Si/sub 14.5/Mo/sub 1.7/ glass-coated amorphous microwires with various geometric ratio /spl rho/ upon axial magnetic field H has been measured for the frequency f range 0.06-15 MHz, driving current amplitude I of 0.75-2 mA, and H up to 2400 A/m. Surface hysteresis loops have been measured by transverse magnetooptical Kerr effect (MOKE). A maximum relative change in the giant magnetoimpedance (GMI) ratio /spl Delta/Z/Z up to around 615% is observed at f=10 MHz and I=0.75 mA in the sample with /spl rho//spl ap/0.98. Application of dc bias current strongly affects the GMI ratio. A maximum of GMI ratio occurs approximately at the same field as the coercivity of surface loops.

Magneto-optical investigation of magnetization reversal in nearly zero magnetostrictive Co-rich wire and microwire

Investigations of the magnetic reversal in amorphous wire of nominal composition (Co 94Fe 6) 72.5Si 12.5B 15 and microwire of nominal composition (Co 1− x Mn x ) 75Si 10B 15 ( X=0.07; 0.11) using transverse and longitudinal magneto-optical Kerr effect have been performed. Changes of the surface hysteresis loops of the amorphous wire after annealing (without and under torsion stress) have been studied. The analysis of the obtained results allows to establish that the outer shell of the as-quenched wire consists of circular domains, in contrast to the annealed wire displaying the domain structure with magnetization directed along the wire axis. Such a modification of the domain structure with thermal treatment could be related to the change of the sign of magnetostriction from negative to positive. The effect of a thermal treatment under torsion stress on the shape of the hysteresis loops of the amorphous wire has also been investigated. The results obtained for this case can be understood by considering the formation of the helical magnetic structure in the wire. The Kerr effect measurements of Co-rich microwires with different Mn content demonstrate the variety of the shapes of magnetization reversal loop, which can be attributed to the change of sign of the magnetostriction. The rectangular shape of the hysteresis loop in circular magnetic field of the microwire with X=0.07 can be interpreted by considering that the magnetization process takes place by large Barkhausen jumps of circular domain structure, while the rectangular shape of the hysteresis loop in axial magnetic field of the microwire with X=0.11 could be attributed to the large Barkhausen jumps within the axial domain structure.

The Structure and Magnetic Properties of Fe-Cu-Nb-Si-B/Fe-Nb-Si-B Bilayer

We have investigated the structure (by TEM and SEM) and basic surface and bulk magnetic properties (by measurement of surface and bulk hysteresis loop and domain structure observations) of a Fe-Cu-Nb-Si-B/Fe-Nb-Si-B bilayer prepared by melt spinning method. We have detected perfect bonding between the two layers of the bilayered ribbon. This bonding produces tangential stress, which influences magnetic properties measured in surface layers at both sides of the ribbon.