Dependence Of Coercive Force Research Articles

Application of the parameters of the remagnetization curve`s spectral characteristics to determine the hardness of ferromagnetic material

The paper discusses the results of the practical application of the harmonic components obtained in the analysis of the magnetic hysteresis loop to determine the hardness of steel. The magnetic characteristics of steel, including the magnetic hysteresis loop, were determined using a DIUS-1.15M magnetic structureoscope. Using the group method of data handling by the value of odd harmonic components, a complex parameter was detected. The weighting coefficients of the influence of harmonic components on the value of the complex parameter were determined. By the example of considering the dependences of coercive force, residual induction and the complex parameter obtained by the method of group argument accounting on the Brinell hardness of the material, it is shown that the complex parameter can be used to determine the hardness with the smallest error.

A Study of Magnetic Properties in a 2D Ferromagnetic Nanolattice through Computer Simulation.

This article investigated the magnetic properties of a 2D nanolattice through computer modeling. A square antidote nanolattice in thin films was considered. For our computer simulation, we used the Heisenberg model. Ferromagnetic phase transition was studied for lattices with pores of various sizes. We determined the Curie temperature based on the finite-dimensional scaling theory. Using Wolf’s algorithm, we simulated the behavior of the system. The dependence of the phase transition temperature on the density of spins was found to be power. Using Metropolis’ algorithm, we calculated a hysteresis loop for an antidote lattice film. The hysteresis loop narrowed as the pore sizes increased. The dependence of coercive force on the size of the nanolattice obeyed the logarithmic law.

A method for quickly evaluating heat treatment quality of 35CrMo steel cylinder using magnetic properties

Seamless steel cylinders are widely used in real-life situations, and heat treatment has an important effect on their service life. The common methods used for heat treatment quality monitoring have many shortcomings, such as destructive operation, high cost and low coverage. To quickly and accurately evaluate the performance of the cylinder after heat treatment, a fast non-destructive testing method is introduced based on the coercive force measurement. The amount of residual stress for 35CrMo steel cylinder before and after heat treatment was evaluated quantitatively by the Metal Magnetic Memory technique, and the structural-mechanical dependence of coercive force was also revealed. Due to the grain refinement and the stress relief, the modified magnetic field index △H and k(x)of 35CrMo steel after heat treated are significantly decreased by 54% and 56%, respectively. Correspondingly, the magnetic coercive force is inversely proportional to the grain size, which is verified by hardness test. The structural-mechanical states of 35CrMo steel cylinder can be justified by measuring their coercive force, which is potential to be used as a reliable, accurate and non-destructive tool for mass production.

Magnetic properties of Co-W thin films

In this paper, the magnetic properties and structure of the Co-W films of different compositions prepared by magnetron sputtering on glass substrates without and with Ta or Ru buffer layers were investigated. The dependences of coercive force on the W content for the studied films were non-monotonic. The peak value of the coercive force of about 400 Oe was observed for the films on glass and Ta layers with W content of 8-9 at. %. The films deposited on Ru layers had a coercive force of 4 times less, and it was practically independent of the W content in a wide range from 6 to 20 at. %.

Cobalt nanoparticles synthesis by cobalt nitrate reduction

The paper describes the synthesis of cobalt nanoparticles in alkali solutions. Co nanoparticles were synthesized by the chemical reduction of a Co(NO3)2 salt alkali solution. The process was followed by hydrogen reduction at high temperature for 30–150 min The TGA and XRD analysis of the obtained samples was carried out. The characteristic size of the particles on each stage of the process was defined as well as its phase composition. The morphology and particle size distribution of the obtained samples were also defined. The dependence of coercive force and saturation magnetization on the diameter of the obtained nano-sized particles were measured as well. The saturation magnetization was found to be constant for particles larger than 40 nm. The reduction scheme for Co nanoparticles was proposed based on experimental results obtained. The average size of the Co nuclei in samples was defined to be 2.9 nm and didn’t change with reduction time. The presence one-molecule water film on the surface of Co nuclei was found on the TEM-images.

Atomic ordering and coercive force of nanocrystalline Fe-Co alloy films

In single crystal films of the Fe0,5Co0,5 alloys grown by the method of vacuum condensation, a metastable condition may be received that is similar to the completely disordering condition. Approximately during ten days after the condensation in the film at the room temperature the short range and then long range atomic ordering is developed. Simultaneously the changes of magnetic anisotropy, electroresistance and coercive force of the films were investigated. This investigations show that the appearance of the shot range atomic ordering increases the electroresistance of films and the long range atomic ordering reduces it. The dependence of coercive force from time to time at room temperature atomic ordering films Fe0,5Co0,5 alloys, and Fe0,75Co0,25. Found that the biggest change Hc (double) is observed in single-crystal films when changing mechanism of magnetization reverse. Most is a consequence of the changes to the crystallographic anisotropy.

Relation between the alignment dependence of coercive force decrease ratio and the angular dependence of coercive force of ferrite magnets

The relation of the coercive force decrease ratio (CFDR) and the angular dependence of the coercive force (ADCF) of ferrite magnets and their temperature properties were investigated.When we compared that against the angle of the magnetization reverse area obtained from these calculation results, which was obtained from the Gaussian distribution of the grain alignment and the postulation that every grain follows the Kondorskii law or the 1/cosθ law, and against the angle of the reverse magnetization area calculated from the experiment CFDR data of these magnets, it was found that this latter expanded at room temperature, to 36° from the calculated angle, for magnet with α=0.96. It was also found that, as temperature increased from room temperature to 413K, the angle of the reverse magnetization area of ferrite magnets obtained from the experiment data expanded from 36° to 41°.When we apply these results to the temperature properties of ADCF, it seems that the calculated ADCF could qualitatively and reasonably explain these temperature properties, even though the difference between the calculated angular dependence and the experimental data still exists in the high angle range.These results strongly suggest that the coercive force of these magnets is determined by the magnetic domain wall motion. The magnetic domain walls are strongly pinned at tilted grains, and when the domain walls are de-pinned from their pinning sites, the coercive force is determined.

Tuning magnetic anisotropy and the damping constant using substrate-induced strain in a FeCo/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure

To investigate how substrate-induced strain affects the magnetic anisotropy and damping constant, FeCo films were deposited onto Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) (0 1 1)-orientated substrates by RF-magnetron sputtering. Interestingly, as the strain, which is controlled by an applied electric field, increases, the magnetic anisotropy is enhanced while the damping constant decreases sharply. The angular dependence of coercive force and magnetoelastic energy were obtained to analyze the mechanism of magnetization reversal under strain modulation. The nonvolatile strain-modulation was demonstrated by the application of different pulsed electric fields. The reversible magnetization processes and low magnetic damping constant can be modulated by the substrate-induced strain, which can contribute to the realization of low-loss strain-mediated spin-transfer-torque based magnetic devices.

Temperature properties of the alignment dependence of coercive force decrease ratio and the angular dependence of coercive force in Nd–Fe–B sintered magnets

The temperature dependence of the coercive force decrease ratio for aligned magnets was investigated from room temperature (296K) to 473K. The temperature properties of the angular dependence of the coercive force were also measured from room temperature to 413K, for comparison against the coercive force decrease ratio.From the temperature dependence of the coercive force decrease ratio of magnets with different alignment, it was found that the coercive force decrease ratio decreased as temperature increased until becoming close to the calculation results that were obtained from the Gaussian distribution for Nd2Fe14B grain alignment and from the postulation that every grain follows the Kondorskii law or the 1/cosθ law.When we compared the angle of the magnetization reverse area obtained from these calculation results and the angle of the reverse magnetization area calculated from the experimental data of the coercive force decrease ratio, it was found that this latter expanded to 30° for Nd13.48B5.76Co0.55Febal. having 0.95 alignment, at room temperature, from 14° that was the calculated angle obtained from the Gaussian distribution and the Kondorskii law. The angular dependence of coercive force of this magnet at room temperature agrees well with the calculation, when σ=31°, which is 30° for the reversed magnetization area, is applied as the standard deviation of Nd2Fe14B grain alignment distribution.For Nd12.75Dy0.84B5.81Co0.55Febal. with 0.96 for alignment, the reverse magnetization area also expanded to 36° and agreed well with the calculation result applied σ=44°, which has 36° for the reverse magnetization area.It was also found that, as temperature increased, the angle of the reverse magnetization area obtained from the experimental data shrunk towards the calculated angle.When we apply these results to the temperature properties of the angular dependence of the coercive force, it seems that the calculated angular dependence of the coercive force can qualitatively and reasonably explain these temperature properties.These results strongly suggest that the magnetic domain walls are strongly pinned at tilted grains. It also suggests that, when such magnetic domain walls are de-pinned from their pinning sites, they leap through several grains with weak pinning force, which determines the coercive force.

Об особенностях формирования магнитных гистерезисных свойств углеродистой стали, легированной кремнием

Magnetic properties of a model steel with 0.6 wt % C doped with Si are studied. It is found that the dependence of coercive force on the tempering temperature (Ttemp) of the model steel doped with 2 wt % Si is due to features of the kinetics of cementite formation in steel. From the temperature dependences of the coercive force HC of the steel, it follows that Si shifts the beginning of the carbide formation to the region of a higher Ttemp. Аn explanation of a high value of НС at Ttemp ≈ 500°C of the steel containing 2 wt % Si compared to that of the plain carbon steel is also given. It is associated with the coercivity of cementite, as a hard magnetic phase with size of precipitates close to the size of single domains.

Analysis of relationship between magnetic property and crystal structure of La 1− xSr xCrO 3 ( [formula omitted], 0.15)

Dependence of dc magnetization, M , of La 1− x Sr x CrO 3 ( x = 0.13 , 0.15) polycrystalline specimens on external magnetic field, H , was measured at various temperatures. At higher temperatures above 274 K and 265 K for the specimens with x = 0.13 and 0.15, respectively, almost linear relationships were observed, indicating paramagnetic property. At the lower temperatures, hystereses, indicating canted antiferromagnetic property, were observed in M – H curves. The temperatures where the magnetic phase transition was observed showed agreement with those where base line shift was observed in differential scanning calorimetry (DSC) measurement. In the M – H curves of La 1− x Sr x CrO 3 ( x = 0.13 , 0.15), saturation magnetization, M s , was not observed at external magnetic fields as high as 70 kOe. At 226 K and 189 K for the specimens with x = 0.13 and 0.15, respectively, structural phase transition from orthorhombic- to rhombohedral-distorted perovskite was observed in DSC curves. At the temperature, abrupt decreases of residual magnetization, M r , and variation of temperature dependence of coercive force, H c , were detected. We regard that the abrupt decrease of M r and the variation of temperature dependence of H c at the structural phase transition temperature can be ascribed to discontinuous variation of Cr–O–Cr angles.

Grain-size dependence of coercive force in sputtered and annealed iron films

Magnetic properties such as coercive force, initial susceptibility, etc., are structure sensitive parameters. Especially, the coercive force depends on the existence of crystal defects such as dislocations and grain boundaries. In this study, the grain-size dependence of coercive force was investigated in an iron film, 150 nm in thickness, deposited by sputtering method on a (001) KCl substrate at room temperature. The grain size of the film was changed from 15 to 120 nm by annealing in a vacuum. The coercive force increased with the increase of grain size and was proportional to the square of grain size. The magnetic domain had a ripple structure when the grain size was smaller than 50 nm. A grain size larger than 50 nm led to an irregular domain wall configuration and the formation of domain walls in the grain.

Magnetic hysteresis of pseudo-single-domain and multidomain magnetite below the Verwey transition

Abstract Hysteresis loops have been measured as a function of temperature between 10 K and room temperature for two size fractions of crushed magnetite: 1–5 μm (pseudo-single-domain, PSD) and 100–150 μm (multidomain, MD). The material under study appears to be fairly close to stoichiometric magnetite, with a Verwey transition temperature of 115 K for the MD sample and 118 K for the PSD sample. For both samples, hysteresis properties below the Verwey transition depend critically on whether or not the samples were cooled through the transition in the magnetic field. For the PSD sample, an even more complex behavior has been observed: temperature dependences of coercive force obtained after zero-field-cooling differ significantly for the demagnetized versus magnetized starting magnetic state.

Coercive force of single crystals of magnetite at low temperatures

SUMMARY The temperature dependence of coercive force H c was studied on well-characterized and stoichiometric millimetre-sized single crystals of magnetite at a series of 16 temperatures from 300 to 10 K using a SQUID magnetometer. H c decreases gradually with cooling to the isotropic temperature, T i =130 K, where the first magnetocrystalline anisotropy constant K 1 becomes zero. H c exhibits a sharp increase at the Verwey transition, T v =120 K, where the structure changes from cubic to monoclinic. In crossing the Verwey transition, H c increases by more than two orders of magnitude, from 20 mT to 2.4 mT, and the shape of the hysteresis loops becomes wasp-waisted. Observed coercivity between 300 K and 170 K varies with temperature as l s /M s , where l s is the magnetostriction constant and M s is the saturation magnetization, indicating that the coercivity in MD magnetite is controlled mainly by internal stress associated with dislocations or other crystal defects. It seems likely that the stable singledomain-like magnetic memory observed in large MD magnetite crystals is due to magnetoelastically pinned domain walls. The discontinuous change in H c at the Verwey transition is controlled by abrupt changes in magnetocrystalline and magnetostriction constants due to crystal deformation from cubic to monoclinic structure.

The coercive force of fine particles of monoclinic pyrrhotite (Fe7S8), between 77 K and 600 K

The temperature dependence of coercive force (Hc) between 77 K and 600 K has been investigated for fine particles of monoclinic pyrrhotite (Fe7S8) of < 1 mm and 1- 30 mm particle sizes. The study has shown that Hc is strongly dependent on temperature, as temperature rises above room temperature (293 K) to near the Curie point (Tc = 593 K). On the other hand, Hc was observed to be weakly dependent on temperature, between liquid Nitrogen temperature (77 K) and room temperature. For the entire temperature range, the data can be expressed satisfactorily as a second order polynomial, Hc (T) = aT 2 + bT + g where a, b and g are numerical constants for a given particle size fraction. The form of this analytic expression is different from that obtained by the authors for the coercive force dependence on temperature which they plausibly expressed in the form Hc (T) µ (1 - T/Tc)q where q < 1, for the temperature range 293-573 K, but which breaks down below 293 K. By considering the variation of the coefficient g with particle size, within the size range 1 and 30 mm it is shown that g(L) = 75.6 L-0.33 kA m-1. JOURNAL OF THE GHANA SCIENCE ASSOCIATION Volume 1 Number 2, January (1999) pp. 90-99

Studies on NdFeB thin films over a wide composition range

The magnetic properties of NdFeB thin films have been studied over a wide range of composition. A detailed study on the effect of composition and other process parameters on the magnetic and structural properties of NdFeB thin films is also presented. An investigation into the effect of the substrate revealed that substrates containing oxygen may not be suitable for preparing these thin films. The coercive force as well as the microstructure of these films were found to depend on the thickness. The composition dependence of coercive force, saturation magnetization and the energy product (Br×Hc) are shown by three dimensional bar diagrams. High coercive force and high energy product were observed at Nd concentrations slightly higher than that of the stoichiometric composition.

Grain growth kinetics and coercivity of soft magnetic NiFe-alloys

Using common models for the dependence of coercive force H c on grain size and for grain growth kinetics a proportionality between H c and 1/√(Dt) is deduced with diffusion coefficient D and annealing time t. This relation has been verified over a wide range of temperature and annealing time for a high purity commercial 80%-NiFe and a 50%-NiFe alloy. The model also allows to determine the activation energy of diffusion using the H c -data and applying an Arrhenius-plot of In[(H c -H co ) 2 t], H co being the minimum attainable coercive force after annealing at very high temperatures. At higher temperatures an activation energy of 3.3 eV for 50%-NiFe and of 2.6 eV for the 80%-NiFe alloy could be deduced, corresponding to the activation energy of self diffusion of about 3 eV for this kind of alloys. At lower temperatures, that is below about 800°C, the activation energy becomes much smaller. and a value of 0.8 eV is obtained, corresponding to the activation energy of grain boundary diffusion.

Calculation of the magnetic parameters of a solid product in inspection by coercive force with the aid of a two-pole magnet : Tabachnik, V.P.; Fedorishcheva, E.E.; Chernova, G.S. Soviet Journal of Nondestructive Testing, Vol. 24, No. 4, pp. 229–235 (Dec. 1988)

The article presents a method of calculating the magnetic conductivity of the inspected part of a massive product and magnetic potential drop on it. Calculation and experiment were carried out for steel 40Kh in the annealed and hardened state. The use of the method of calculating induction along the center lines of regions in which the flux is concentrated in the magnetization of a massive product by a two-pole electromagnet, and with the experimental dependences of coercive force and maximum differential permeability on the maximal values of induction on partial hysteresis cycles taken into account, makes it possible with accuracy sufficient for practice to find the drop of the magnetic potential on the investigated segment of the product and its magnetic conductivity.

Brillouin light scattering from ultrathin iron films (abstract)

The thickness dependence of the magnetization, magnetic anisotropy, coercive forces, and g factors of an ultrathin Fe film are studied by Brillouin scattering and magneto-optic Kerr effect at room temperature. The wedge Fe film was fabricated on a Ag buffer with GaAs[100] substrate by means of molecular-beam epitaxy technique. The epitaxial growth and crystalline quality of the specimen structures were controlled by reflection high-energy electron diffraction, spot profile analysis-low energy electron diffraction (SPA-LEED), and Auger electron spectroscopy techniques. The measured magnetization and thickness dependence [1.5–16 monolayer (ML)] are compared with the theoretical predictions. Two magnetic order phases are identified, paramagnetic for 1.5 ML and magnetic for 2 ML and thicker film. It is found that g factor is 7% smaller in 1.5 ML film than that in the bulk. A nearly linear thickness dependence of coercive force in this film is observed. The establishing of the bulk in-plane anisotropy shows similar behavior as that of the magnetization, but with a delay in thickness. No apparent perpendicular magnetic anisotropy is observed at room temperature in this sample, which may be related to the nearly perfect in-plane lattice matching between the sandwiched Fe layer and Ag buffer and capping layers.

Synthesis of Nd-Fe-B thin films with high coercive force by cosputtering

NdFeB thin films were prepared by cosputtering of the individual elements and the magnetic properties were studied as a function of the concentration of Nd and B in the films. The dependence of coercive force, saturation magnetization and the energy product (B/sub r//spl times/H/sub c/) on the composition are presented by three dimensional diagrams. High coercive force and high energy product was observed at Nd concentrations slightly higher than the stoichiometric composition. For a fixed composition, a dependence of coercive force as a function of thickness of the film was observed. The microstructure of the films also showed a variation as a function of thickness.