Amorphous ribbons of composition (Co_{0.95}Fe_{0.05})_{100-x}Si_{0.4x} B_{0.6x}, with x=25 and 30 were prepared by the melt-spinning technique. Current annealings at 600 mA were performed for annealing times between 15 s and 60 min. The magnetoimpedance response was investigated by submitting the ribbons to ac currents at frequencies in the 10-200 kHz range, with amplitudes between 1 and 15 mA (rms), and measuring their voltage response. The observed results show that a transverse anisotropy is induced by the thermal treatments, which can be evaluated by means of the magnetoimpedance effect. Due to its lower Curie temperature, the x=30 ribbons exhibited lower sensibility to the current annealings.
Influence of composition variations on the physical and chemical properties of rapidly quenched NANOPERM-type, FeNbCuB, and FINEMET-type, Fe(Ni)NbCu(Si)B, alloys in amorphous states, is investigated by Mössbauer spectroscopy, magnetic and electrochemical methods. While the partial substitution of Si for B leads to weak effects, that of Ni for Fe results in pronounced changes of both magnetic properties and chemical stability.
Development of the atomic directional ordering in the Fe_{43}Ni_{43}Zr_7Cu_1B_6 alloy, during its conventional the same as after transverse magnetic field annealing, was experimentally studied by the amplitude dependence of susceptibility and hysteresis loops measurements, respectively. Diffusion processes of the mobile atoms caused perminvar effect, decrease of the initial susceptibility, increase of the critical field, and linear shape of the hysteresis loop. Uniaxial magnetic anisotropy, created during magnetic field annealing of the FeNiZrCuB alloy, was confirmed also by observation of the surface domain structure.
Magnetic field dependences of the piezomagnetic dynamics, magnetomechanical coupling and elasticity moduli in the Fe_{73.5}Cu_{1}Nb_{3} Si_{13.5}B_{9} alloy in an as-quenched state and annealed in vacuum for 1 h at 450°C were investigated. The maximum value of the magnetomechanical coupling coefficient was equal to 0.15 for the as-quenched state and 0.7 after annealing at 450°C. The changes of the elasticity moduli (ΔE effect) from about 60 to 180 GPa were observed after annealing at this temperature. These changes are connected with magnetostriction (equal to 25.8×10^{-6} at saturation), internal stresses, defects, mechanical, magnetic and heat treatment history.
Magnetic and magnetoelastic properties of the Fe_{73.5}Si_{16.5}B_{6}Cu_{1}Nb_{3} alloy change considerably during nanocrystallization process. Improvement of magnetic properties is accompanied by the decrease in piezomagnetic parameters such as magnetomechanical coupling and ΔE-effect.
The influence of the magnetic field annealing on the magnetoimpedance effect has been investigated in rapidly quenched (Fe_{0.5}Ni_{0.5})_{78}Nb_{7}B_{15} monolayer and bilayer thin ribbons. The highest impedance ratio value (ΔZ/Z)_{max}=72% and the maximum field sensitivity η_{max}=12 %/Oe was obtained in the bilayer ribbon, annealed under longitudinal magnetic field at 773 K that exhibited nanocrystalline structure. The higher values of (ΔZ/Z)_{max} in bilayer ribbons, as compared to their monolayer counterparts, are attributed to the increased ratio of their thickness to the penetration depth.
Ferromagnetic vortex core switching is investigated using micromagnetic simulations. For that the OOMMF program is used together with a temperature extension we have developed recently. This is a continuum micromagnetic approach, where the well-known Landau-Lifshitz-Gilbert equation (valid for zero temperature) is replaced by the Landau-Lifshitz-Bloch equation. In our research we simulate switching of a ferromagnetic vortex core in a flat disk (diameter 200 nm, thickness 20 nm) with material parameters that resemble permalloy. Temperatures in the range 400 K to 700 K are considered. Switching itself is caused by application of a very short oscillating magnetic pulse. Parameters used resemble conditions met in the experiment: oscillation period 141 ps (equal to the peak width) and amplitude 60 mT. Surprisingly, no large temperature- or discretization dependence is found. Reasons for that are discussed.
Influence of heat treatment on magnetic properties of amorphous Hf₂Co₁₁B alloy was investigated. Hard magnetic phase, characterized by high magnetic anisotropy, appears during crystallization. The highest coercive field equal to 1.86 kOe, was obtained for sample annealed in third crystallization stage. Longer heat treatment at T_{a} = 650°C leads to decrease in coercive field, which can be the result of excess of the HfCo₃B₂ phase volume fraction and additionally eutectoid transformation of hard magnetic phase into soft magnetic Co₂₃B₆ and fcc-Co. Decrease of volume fraction of hard phase is confirmed by the remanence ratio m_{r}. Value of m_{r}, for T_{a} = 650°C, is decreasing with annealing time from 0.4 to 0.27 for 30 min and 120 min, respectively. The magnetocrystalline anisotropy constant K₁ increases from 2.23 Merg/cm³ for the amorphous ribbon to 15.84 Merg/cm³ for the sample annealed at 650°C for 30 min.
We report on structural and magnetic properties of glass-coated microwires of Ni-Mn-Ga-based Heusler alloys. Structural characterization of the as-prepared microwires revealed that they have a cubic structure at room temperature. It is shown that magnetic properties of microwires can be tailored by heat treatment as well as by removing the glass coating. Specifically, annealing of the microwires has a marked influence of the Curie temperature T_{C} which increases significatly in the heat-treated samples. Release of internal stresses in the microwires by removing the glass coating causes magnetization and the Curie temperature to decrease. This allowed us to conclude that in the studied microwires the magnetostriction constant is positive and estimate the value of internal stresses as being roughly equal to 1.5 GPa.
The effect of pulse annealing on magnetization processes in FINEMET-type alloy in weak magnetic fields (the Rayleigh area) is studied in this paper. Rapidly quenched FINEMET ribbon in the original amorphous state was chosen for the study. The significant differences in behavior of studied materials are ascribed to the differences in internal mechanical stresses, which bring about the changes in total magnetic anisotropy and consequently also changes in domain walls thickness.
The effect of heat treatment in applied magnetic field on the induced anisotropy and domain structure of (Fe_{1-x}Co_x)₇₉Mo₈Cu₁B₁₂ (x=0, 0.2, 0.5) nanocrystalline alloy system was investigated. A heat treatment of Co-doped samples under the application of longitudinal magnetic field resulted in squared hysteresis loops characterized by very low coercive field values. Sheared loops with tunable slope and good field linearity were obtained after annealing in transverse magnetic field. Corresponding domain structure showed uniform character, oriented in the direction parallel or perpendicular to the ribbon axis after longitudinal or transverse magnetic field annealing, respectively. No effect of magnetic field annealing was found in Co-free sample. Correlations between Co-doping, the Curie temperature, and soft magnetic properties after magnetic field annealing are discussed.
In this paper possibility of application two-dimensional vector Preisach model for bulk materials was investigated. Physical magnetization mechanisms in bulk cores and thin ribbons were analyzed. Model is based on collection of the Preisach planes which describe material state in different angles on rotation plane. Presented model exhibits good conformity with experimental data for bulk as well for ribbon shaped cores. Model includes anisotropy and describes not only mean magnetization vector, but also distribution of magnetic moments for different angles.
In this work, we report on the effects of high static magnetic field on the formation of desirable crystallographic orientation of grains ("rotating" cube) during the primary recrystallization of non-oriented steels. Vacuum degassed non-oriented steel with the silicon content about 1 wt% was taken from industrial line after final cold rolling with 80% of deformation and then it was subjected to the laboratory annealing at temperature of primary recrystallization. Whole annealing process was carried with and without the applied external magnetic field of 14 T. The analysis of crystallographic orientation of experimental material was studied by electron backscattered diffraction technique. The microstructural and textural observations have shown a small difference in average grain size between samples annealed with and without magnetic field as well as increase of the "rotating" Cube component and decrease of the intensity of deformation texture by application of magnetic field. The magnetic measurements show that the coercivity value of the sample annealed in the magnetic field of 14 T can be reduced by approximately 3% in comparison with sample annealed under the zero field conditions.
Effects of slight nonstoichiometry in Gd_{1+x}Ba_{2-x}Cu_{3}O_{7-δ} compounds on superconducting and magnetic properties were studied. The series of single-phase samples of Gd_{1+x}Ba_{2-x}Cu_{3}O_{7-δ} with composition deviation x from the stoichiometric value of 0 to 0.1 and to -0.1 were synthesized by the solid-state reaction method from Gd_{2}O_{3}, BaCO_{3} and CuO precursors, sintered at the temperature of ~ 1000°C in flowing oxygen and annealed at 450°C for 24 h.
The objective of this study is to prepare and study magnetic properties of biological magnetic nanoparticles (magnetosomes) as a product of biomineralization process of magnetotactic bacteria Magnetospirillum sp. AMB-1. From temperature dependence of remanent magnetization and coercive field the Verwey transition is clearly seen at 105 K as a consequence of the large anisotropy along the chains of magnetosomes.
Cultivation process was changed three times. The culture medium was enriched by more amount ferric quinate (FQ magnetosomes sample) and more amounts Wolfe's vitamin solution (WVS magnetosomes sample) comparing to normal culture medium (NP magnetosomes sample). NP sample of magnetosomes shows zero coercivity and behaves superparamagnetically. The increase of coercivity (6.5 Oe for WVS and 20 Oe for FQ) may be caused by higher value of shape anisotropy and reveals stronger magnetic correlations between particles of magnetite chains.
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