Papers by Keyword: Coercive Force

Abstract: The porous structure and magnetic properties of nanostructured Fe₃O₄/C composites based on wheat straw were investigated in this work. The synthesis was carried out by a one- and two-step method using FeCl₃ and ZnCl₂ as activating agents. X-ray diffraction methods have shown the presence of an additional phase of magnetite Fe₃O₄ in both synthesized composites, along with the amorphous carbon phase. Magnetic measurements have shown that the composite synthesized in one step has better magnetic properties, in particular, a higher specific saturation magnetisation. However, the samples of the composite synthesized in two steps are characterised by a higher content of micropores and mesopores, which causes an increase in the specific surface area to 884 m²/g compared to 405 m²/g for the samples synthesized in one step. Based on the dependence of the coercive force on the particle diameter in Fe₃O₄ dispersions, it was found that the average size of the magnetite particles is ~25 nm for both synthesized magnetoresponsive composites.

Abstract: The change in the coercive force of the 10kp5 steel specimens subjected to cyclic loading and impulse current has been studied. The choice of processing methods, including their combination in a certain sequence, was shown to provide the best plastic or strength properties of metal materials. The feasibility and good perspectives of express assessment of the effectiveness of the chosen method or methods of processing metal materials by magnetic properties, e.g., coercive force, without resorting to mechanical tests with the destruction of specimens, are noted. The highest changes towards increase in strength and coercive force in the 10kp5 low-carbon steel have been found after cyclic loading and in a combined mode with cyclic loading at the final stage. The optimal combination of cyclic loading and pulse current can make it possible to control the strength and magnetic properties of ferromagnetic materials.

Abstract: The mechanical properties of steel often determine to a greater extent its performance characteristics, including service life of the equipment. Often, for operational control of mechanical properties, magnetic parameters are used such as, for example, the coercive force. Both mechanical and magnetic properties of steel are associated precisely with the structure of the material. The influence of the structure on these properties became known a long time ago, however, in similar works, the influences exerted by the structure with different degrees of dispersion are not considered. In this work, the goal was set to consider the effect of grain size difference on the magnetic and mechanical characteristics of steel.

Abstract: The simulation of the Sm(Co, Fe, Cu, Zr)_7.5 type alloy domain structure formation after various thermal treatments was carried out by FMRM program based on a phenomenological approach to the analysis of the uniaxial highly anisotropic ferromagnets demagnetization processes. It is shown that the domain structure of the alloy in the thermally demagnetized state expands as the coercive force of the alloy decreases. It is noted that the domains size increasing process is associated not only with a decrease in the coercive force but also with a change in the influence of the magnetostatic interaction.

Abstract: Scaling of minor hysteresis loops in the amorphous alloy Co₆₆Fe₃Cr₃Si₁₅B₁₃ with a very high initial permeability (more than 150000) and low coercivity (about 0.1 А/m) has been studied. In weak magnetic fields and in the region of maximal growth of permeability a similarity of minor loops was detected. Analytical expressions for hysteresis losses are derived which provide a good accordance of calculations with the results of measurements.

Abstract: At the present time the assessment of stress-strain state of steel structures uses the results of coercive measurements. However, the methods presented in various works are contradictory and not deprived of errors of a methodological nature, which may lead to erroneous conclusions. This article reveals the analysis of disadvantages of the known methods and proposes possible ways to eliminate these shortcomings.

Abstract: Magnetoresistive effect and electrotransport properties of Fe-NbO (13 ≤ Fe, at.% ≤ 80) thin films annealed at 600 °C has been investigated. It has been established that the samples structure contains three main phases Fe, NbO₂, Fe_2.9O₄. Maximum of magnetoresistance in the samples does not exceed 0.3%, a coercive force is ranging from 150 to 370 Oe, depending on the Fe concentration. It is assumed that the films have a granular structure. Magnetoresistance and coercive force values, as well as the correlation between the magnetoresistance and the magnetization of the Fe-NbO samples are uncharacteristic for granular systems. It is assumed that uncharacteristic properties are due to the significant influence of ferrite Fe_2.9O₄ on the magnetic properties and electrotransport of the Fe-NbO films.

Abstract: Structure and magnetic properties of FeNi/Ti multilayers prepared by magnetron sputtering were studied. The dependences of the spontaneous magnetization and hysteresis features of the films on the thickness of the magnetic layers were established. It was shown that these properties were to a large extent determined by interlayer interfaces, in which the effective magnetization decreases. The possible reason for the interface peculiarities was the interlayer mixing. The presence of (FeNi)Ti phase which was formed by the interdiffusion of FeNi and Ti layers was confirmed by X-ray diffraction measurements.

Abstract: Thin Co films were fabricated by DC magnetron sputtering. The effect of argon pressure on the microstructure, surface morphology and magnetic properties of the samples was systematically studied. It was found that with the increase of argon pressure, the sharpness of the crystalline texture of the samples declines, the roughness of film surfaces and the coercivity of the films increase. Based on these results, a Co/Cu/Co pseudo spin-valve system was designed and the corresponding structures were fabricated. The difference in coercivity of magnetic layers was obtained by deposition of the Co layers at different Ar pressures. Change of the resistance of this trilayer is induced at a moderate field by the spin rotation in the soft layer with lower coercivity.

Abstract: Magnetic nondestructive testing methods including eddy current testing, magnetic memory, magnetic Barkhausen noise and so on are widely used in testing mechanical properties of ferromagnetic parts. Experiments were done to study the relationship between hardness and magnetic properties of ultra-high strength steel (UHSS), which plays an important role in automobile industry. The magnetic properties of UHSS specimens with different hardness were studied. The result shows that there is a strong connection between hardness and magnetic properties. Coercive force of UHSS is proportional to the hardness. This can be used to explain certain mechanism of magnetic nondestructive testing method such as connection between hardness and Barkhausen noise.