Effects of sulfur content and slab reheating temperature on the magnetic properties of fully processed nonoriented electrical steels

The effects of sulfur content and slab reheating temperature on the magnetic properties of four fully processed nonoriented electrical steels have been investigated. Four slabs of nonoriented electrical steels with sulfur content in the range of 0.0006–0.0126 wt% were reheated to 1100, 1200, and 1300 °C, respectively. Then, they were hot rolled and annealed at 700 °C, cold rolled at the same condition and annealed at 820 °C in the salt bath furnace for 1 min to simulate continuous annealing. The ac core loss, dc hysteresis loss, and ac and dc permeability were measured at 15 kG inductions. It was found that the amount of inclusions in the hot-rolled bands increased with increasing slab reheating temperature and increasing sulfur content in steels. After final annealing, grain sizes of cold-rolled steel sheets decreased with increasing sulfur content and increasing slab reheating temperature. The main preferred orientations in the final annealed steel sheets were (0 1 1) 〈1 0 0〉 and (1 1 1) 〈u v w〉 γ fiber texture. Steel sheets containing 0.0032 and 0.0060 wt% sulfur developed a more stronger (0 1 1)〈1 0 0〉 texture than other steel sheets. However, steel sheets containing 0.0126 wt% sulfur had the weakest (1 1 1)〈u v w〉 texture during slab reheating at temperatures higher than 1200 °C. Both ac core loss and dc hysteresis loss increased with increasing slab reheating temperature and increasing sulfur content in steel sheets. Both ac and dc permeability decreased with increasing slab reheating temperature and increasing sulfur content in steel sheets. If sulfur content decreased from 0.0060 to 0.0032 wt%, there were great improvements in ac core loss, dc hysteresis loss, and ac and dc permeability. However, eddy current loss was almost independent of the sulfur content and slab reheating temperature.     

Evolution of magnetic phase at low aging temperature in a heavily cold-drawn stainless steel fiber

The evolution of the magnetic phase upon aging at 300–520 °C in a heavily cold-drawn AISI 316L austenitic stainless steel fiber was studied using thermomagnetic analysis (TMA) and magnetic force microscopy with a heating stage. An increasing trend of magnetization from 50 °C to around 470 °C in the heating curves of TMA in austenitic stainless steels after a cold-drawing process was observed. No significant M_s temperature signal in the TMA curve at cooling indicated an increase in magnetization upon cooling period without significant phase transformation. A series of in situ magnetic force microscopy observations reveal a growth of the magnetic domain structure after aging at 300 °C for 2.5 h. Results show that the ferromagnetic increase during aging at lower annealing temperature resulted from the growth of martensite.     

Magnetic properties of field-annealed FeCo thin films

Fe₅₀Co₅₀ thin films with thickness of 30 and 4 nm have been produced by rf sputtering on glass substrates, and their surface has been observed with atomic force microscopy (AFM) and magnetic force microscopy (MFM); MFM images reveal a non-null component of the magnetization perpendicular to the film plane. Selected samples have been annealed in vacuum at temperatures of 300 and 350 °C for times between 20 and 120 min, under a static magnetic field of 100 Oe. DC hysteresis loops have been measured with an alternating gradient force magnetometer (AGFM) along the direction of the field applied during annealing and orthogonally to it. Samples with a thickness of 4 nm display lower coercive fields with respect to the 30 nm thick ones. Longer annealing times affect the development of a harder magnetic phase more oriented off the film plane. The field applied during annealing induces a moderate magnetic anisotropy only on 30 nm thick films.     

Real time dynamic domain observation in bulk materials

The paper briefly reviews the development of domain observation techniques used to study basic properties of electrical steels. A new real-time, dynamic, high magnification domain observation technique is presented as an example of a state-of-the-art system, capable of imaging non-repetitive domain wall motion at power frequencies. Advantages of real-time domain observation over stroboscopic magneto-optic studies are presented and the need for real-time observations in developing future loss theories is proposed. Possible relationships between Barkhausen noise, hysteresis and non-repetitive wall motion in electrical steels are suggested and finally examples of non-repetitive wall motion in other magnetic materials are illustrated.     

Magnetization reversal in amorphous gadolinium-cobalt films with a radial gradient of magnetic properties

The integral characteristics of magnetization switching in amorphous gadolinium-cobalt films with perpendicular anisotropy are studied by visualizing the domain structure and measuring magnetooptic hysteresis loops. The films have a radial gradient of magnetic properties that is due to a spatially nonuniform thermal field. Magnetization switching in those film areas where the domain wall motion depends only on the coercive force is simulated in simple terms. In a first approximation, local events of magnetization switching are shown to take place independently of each other and the net hysteresis loop can be represented as a sum of the local loops.     

Microwave properties of composites with chromium dioxide

The permittivity and permeability of composites filled with CrO₂ powder are measured within the frequency range from 0.05 to 12 GHz. A sharp line of magnetic absorption is detected near 8 GHz. The effects of magnetic bias and remanence on the permittivity and permeability spectra are analyzed. The hysteretic behavior of dynamic permeability is observed for both parallel and perpendicular bias orientations relative to the microwave magnetic field. The effect is due to switching of the magnetic texture under bias equal to coercive field. At 50 MHz the parallel bias close to coercive field affects permeability much stronger than the perpendicular one. At 10 GHz the effect of perpendicular bias is higher than that of the parallel one. The effect of remanence on the microwave permeability is negligible. The 3 kOe parallel bias suppresses the line of magnetic absorption and decreases the conductivity of the composite and its microwave permittivity. This can be attributed to the magnetostatic interaction of inclusions in the vicinity of the percolation threshold.     

Effect of water quenching process on the microstructure and magnetic property of cold rolled dual phase steel

The effects of water quenching process on the microstructure and magnetic property of cold rolled dual phase steel are investigated. Correlations of microstructure, magnetic properties and water quenching parameters are established. The results show that the microstructure of the dual phase steels mainly consists of the ferrite and martensite phase, the martensite volume fraction increases gradually on increasing the holding and quenching temperature. It is found that magnetic properties of dual phase steel are very sensitive to the quenching process. Based on the minor hysteresis loop results, the coercivity and hysteresis loss increase obviously with the increase of quenching temperature, while the remanent induction and the maximum permeability tend to decrease. Furthermore, the magnetic domain structure of the ferrite phase in the presented dual phase steel is observed by magnetic force microscopy. The mechanism of the magnetic property varying with the quenching process is also discussed.     

The effective properties of macroscopically nonuniform ferromagnetic composites: Theory and numerical experiment

Various theoretical models (self-consistent field, local linearization, and percolation theory methods and an analytic solution of the linear problem for an ordered medium) for calculating the magnetostatic properties of two-phase composites containing one ferromagnetic phase were considered. The concentration and field dependences of the effective magnetic permeability were found. A method for determining the coercive force and remanent magnetization as functions of the ferromagnetic phase concentration was suggested. Numerical experiments were performed for composites with a periodic distribution of circular inclusions. The results were compared with the analytically calculated effective magnetic permeability.     

To the theory of dynamic magnetization and magnetic reversal of a ferromagnet

The dynamics of motion of domain boundaries is investigated for samples with low magnetostriction. Changes in the coercive force parameter and maximum magnetic permeability are investigated for various magnetic materials depending on the dislocation density. It is established that an increase in the velocity of domain boundaries causes the decrease of the coercive force and the increase of the maximum magnetic permeability. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 26–32, March, 2006.     

On the Steinmetz hysteresis law

The behavior of the Steinmetz coefficient has been described for several different materials: steels with 3.2% Si and 6.5% Si, MnZn ferrite and Ni–Fe alloys. It is shown that, for steels, the Steinmetz law achieves R²>0.999 only between 0.3 and 1.2 T, which is the interval where domain wall movement dominates. The anisotropy of Steinmetz coefficient for non-oriented (NO) steel is also discussed. It is shown that for a NO 3.2% Si steel with a strong Goss component in texture, the power law coefficient and remanence decreases monotonically with the direction of measurement going from rolling direction (RD) to transverse direction (TD), although coercive field increased. The remanence behavior can be related to the minimization of demagnetizing field at the surface grains. The data appear to indicate that the Steinmetz coefficient increases as magnetocrystalline anisotropy constant decreases.     

Magnetic force microscopy characterization of heat and current treated Fe40Ni38Mo4B18 amorphous ribbons

The domain structure of a magnetostrictive Fe₄₀Ni₃₈Mo₄B₁₈ amorphous ribbon has been studied using magnetic force microscopy (MFM) at room temperature. First, the evolution of the magnetic domain patterns as a function of the annealing temperature has been investigated. In samples heat treated at 250 and 450 °C for 1 h, a transformation from 90° to 180° domain wall has been clearly observed, while the sample heat treated at 700 °C for 1 h showed a magnetic phase fixed by the crystalline anisotropy. Additionally, the evolution of the magnetic domain structure by applying a DC current was recorded by the MFM technique. For current annealed samples at 1 A for 1, 30 and 60 min, a transformation between different domain patterns has been observed. Finally, in samples treated by the current annealing method under simultaneous stress, an increase of the annealing time gives rise to a different magnetic structure arising from the development of transverse magnetic anisotropy.     

On the inclusion theory of coercive force

Randomly distributed spherical inclusions are considered in the derivation of an expression for the coercive force of a ferromagnetic single crystal, containing two magnetic domains separated by a single Bloch wall.     

Effect of heat treatment and elastoplastic deformation on magnetic properties of 50Ni2Mo powder steel

The paper studies the effect of heat treatment modes and uniaxial tension on the magnetic properties, internal stress and specific resistance of 50Ni2Mo powder steel. It is shown that when treated and mechanically loaded in the elastic range and weak magnetic fields, the steel reveals anomalous behavior of its magnetic characteristics such as coercive force, maximum permeability and residual induction. The observed anomalous behavior is analyzed in the framework of physical mesomechanics and is associated with porosity of the powder material. It is demonstrated that physical mesomechanics and magnetic measurements hold promise as an efficient tool of research in porous ferromagnetic materials in various effective external fields. The thus studied magnetic characteristics allow efficient control of heat treatment modes of 50Ni2Mo powder steel.     

High-frequency properties of thin amorphous ribbons

Magnetic energy losses have been investigated in Co-based near-zero-magnetostriction amorphous ribbons from DC to 10 MHz. Attention has been devoted to the properties of field-annealed ribbons thinned down to 5.8 μm and their behavior at high frequencies. A rationale is provided for the frequency dependence of the magnetic losses over the investigated many-decade range through analysis of the loss components. Ribbons annealed under transverse field benefit by limited irreversible domain wall activity and correspondingly reduced hysteresis and excess losses. Based on the near-linear response of the material and the permeability–energy loss relationship, the separate contributions of domain wall displacements and rotations to the magnetization process and the related dissipation effects are singled out at all frequencies. Very thin amorphous ribbons are shown to display lower loss and higher permeability (i.e. higher Snoek's product) than Mn–Zn ferrites at all frequencies.     

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.     

Der einfluss des stanzens auf die magnetischen eigenschaften von elektroblech mit 1% silizium

The influence of punching on the magnetic properties of fully annealed electrical steel sheet with 1 % Silicon has been investigated. By comparing to an Epstein sample, which had its deformed edges carefully removed, it was found that the total power loss increases and the permeability decreases with increasing the specific cut edge. At a length of 100 m/kg the increase P 1.0 is about 30% when samples were cut with a sharp tool and even 40% for a blunt tool. The greatest change of the induction occurs in the range of maximum permeability. At 100 m/kg cut edge the decrease is about 70%: an influence of the clearance on the magnetic properties could not be shown clearly; the area of edge hardening was 0.35 mm in width; there was no influence of tool wear.Original magnetic properties have been obtained after box annealing at 700°C/1 h in dry nitrogen.     

Study of the coercive force in ferromagnetic dysprosium metal by RF field enhancement

The RF field enhancement factor η is calculated for the domains and domain walls of ferromagnetic Dy metal. In the domains η ? 30, while in the walls it depends on the coercive force which limits the wall motion. The study of η from spin echo signals of nuclei in the walls is used to determine this coercive force in powder of Dysprosium metal, before and after annealing.     

Measurement of the magnetic moment in a cold worked 304 stainless steel using HTS SQUID

The magnetic properties of stainless steel have been investigated using a radio frequency (RF) high-temperature superconductivity (HTS) SQUID (Superconducting QUantum Interference Device)-based susceptometer. The nuclear grade 304 stainless steel is nonmagnetic at a normal condition but it changes to a partially ferromagnetic state associated with martensitic transformation under a plastic deformation. The magnetic moment of the 304 stainless steels was increased with an increasing cold work rate, and decreased with an increasing annealing temperature. The change of mechanical properties such as yield strength and ultimate tensile strength (UTS) are also analyzed in terms of deformation-induced martensitic transformation.     

Determination of average domain size on permalloy and perminvar by means of complex permeability measurements

Our experiments were performed on industrial purity materials of 0.10–0.35 mm strip thickness. We tried to apply both the Polivanov bowing wall and the Pry-Bean rigid wall model for characterizing the domain structure of the materials. We proved experimentally that the main features of domain structure are in agreement with the assumptions of the bowing wall model. By means of fitting theoretical spectra on measured complex permeability spectra we determined the average size of domains as a function of thickness and annealing temperature. The number of domains related to one grain could be associated with changes of initial permeability and coercive force.     

Nanocrystalline magnetic PrFeCrB alloys

Ribbons of Pr₅Fe_77−xCr_xB₁₈ (x=0$x=0$, 1, 2, 2.5, 3, 4, 5) were produced by melt spinning and then annealed to develop an enhanced-remanence nanocrystalline magnetic material. These nanocomposites with Cr present a coercive field at least 50% higher than the Cr-free ones, which makes them promising materials for bonded magnets. Four different types of annealing were used in order to develop the nanocrystalline state and to optimize the magnetic properties of these alloys. The first was a conventional annealing, where the ribbons were wrapped in a tantalum foil and annealed in an argon atmosphere, but not encapsulated. The second was a flash annealing, where the ribbons were annealed by passing a current through them. The third was a conventional annealing in an external magnetic field. Finally, the fourth was a conventional annealing, where the ribbons were wrapped in a tantalum foil and encapsulated in quartz tubes with argon gas and then annealed. The annealed samples were studied by magnetic measurements, X-ray diffraction, scanning and transmission electron microscopy and atomic force microscopy. The best magnetic properties are found for Pr₅Fe₇₄Cr₃B₁₈, annealed by the fourth method, which resulted in the lowest oxygen content in the annealed nanocrystalline material as confirmed by scanning electron microscopy. The value for the coercive field for this composition is at least 50% higher than for the material without Cr (≈560 vs. ≈320 kA/m) and 40% higher than for the Nd₂Fe₁₄B/Fe₃B nanocomposite with Cr. Curie temperature measurements and X-ray diffraction data showed that the main phases present in all the samples are Pr₂Fe₁₄B, Fe₃B and α-Fe, Pr₂Fe₁₄B being the majoritary phase. From Curie temperature measurements it was also found that Cr atoms preferentially dissolve in the Fe₃B phase.