Small Angle Magnetization Rotation Method Research Articles

Angle Magnetization Rotation Method for Characterizing Co-Rich Amorphous Ferromagnetic Microwires

A low-frequency model of the magnetization reversal of a microwire is developed for those cases when the microwire magnetization response can go beyond the linear approximation. The analysis of the influence of external magnetic fields on the process of magnetization reversal of the microwire, including the hysteresis mode, was performed. The characteristic dependences of the amplitude of the electromotive force, U2f, arising in the pick-up coil wound around the microwire are obtained. It was established that, in the region of relatively small-acting circular and longitudinal magnetic fields, the U2f signal could have a region with the opposite sign. An extended small-angle magnetization rotation method was used to verify the proposed model and test glass-coated, amorphous, Co-rich microwires. During the experiments, the amplitude of the second harmonic, U2f, arising in the pick-up coil when an alternating electric current with the frequency f flows through the microwire, was measured as a function of the applied longitudinal magnetic field at various mechanical tensile stresses. The effective anisotropy field, the magnetostriction constant, and the residual quenching stress of the investigated microwires were determined by comparing the theoretical and experimental data.

Investigation of Cu/NiFe composite wires by SAMR method

Composite Cu/NiFe wires with two different compositions of electrolytic NiFe layers were investigated by the small angle magnetization rotation (SAMR) method. From the measurements the induced anisotropy and the saturation magnetostriction constants were determined. The measurements were compared with the theoretical model based on the quasistatic approximation. The experimental results well agreed with the theory.

Co-rich Amorphous Microwires with Improved Giant Magnetoimpedance Characteristics Due to Glass Coating Etching

Glass-coated Co-rich amorphous microwires are very promising for the development of tiny magnetic sensors that can be used in portable electronic devises. In this study, a substantial decrease in the residual quenching stress in Co-rich microwires is achieved by reducing the thickness of the glass coating by means of precise etching of the wire in a specially designed gel. This effect is confirmed experimentally by means of the small-angle magnetization rotation method as well as by direct measurement of the off-diagonal component of the giant magnetoimpedance (GMI) tensor of wires with different thicknesses of glass coating as a function of the applied magnetic field. A reduction in the thickness of the glass coating to the range of 0.5–2.0 µm resulted in a nearly twofold increase in the steepness of the off-diagonal GMI component of the studied Co-rich microwires. Therefore, this method can be used to improve the sensitivity of miniature magnetic sensors to weak external magnetic fields.

Glass shell etching to control residual quenching stress in Co-rich amorphous ferromagnetic microwires

The magnetic properties of amorphous glass coated microwires are determined mainly by the distribution of residual quenching stresses over the microwire cross section. In this paper a control of the residual quenching stresses in amorphous ferromagnetic microwires is achieved by changing the microwire glass shell thickness by etching. To this end, a special gel is synthesized for precision glass shell etching of series of Co-rich microwires. The use of the gel provides a possibility of uniform etching of the microwire glass coating at a rate of 0.2–3.2 μm/h depending on the amount of glass already removed, a surface roughness being about 40–100 nm. It is also possible to completely remove the glass shell of the microwire without damage its metallic nucleus. The small angle magnetization rotation method has been used to determine the change in the amplitude of the residual quenching stress with a gradual decrease of the glass shell thickness of microwires of composition Co67Fe4Ni2Mo2B11Si14 and Co71Fe4Si10B15. It is found that the amplitude of the residual quenching stress deceases by 40–50% in average after removing of the layer of 1 μm thickness from the glass coating.

Mechanical properties and internal quenching stresses in Co-rich amorphous ferromagnetic microwires

Abstract The whole set of geometrical, mechanical and magnetic parameters of Co-rich amorphous ferromagnetic microwires very promising for the development of sensitive stress and Giant Magneto-Impedance sensors have been determined by means of scanning electron microscopy, selective nanoindentation and small angle magnetization rotation method. The magnetostriction constants obtained are sensitive to the true microwire compositions. The experimentally estimated amplitudes of the residual quenching stress are mainly determined by the ratio of the inner and outer wire diameters. They are found to be in good correspondence with the theoretical values calculated based on the theory of viscoelasticity.

Investigation of the properties of Co-rich amorphous ferromagnetic microwires by means of small angle magnetization rotation method

The amplitude of the second harmonic of the electro-motive force occurring in the receiving pick-up coil when alternating electrical current is flowing through the microwire is measured as a function of applied external magnetic field, at different mechanical tensile stresses. In addition, an analytical expression for the amplitude of the second harmonic of the electro-motive force is derived. Comparing the experimental and theoretical data the saturation magnetization, the magnetostriction constant and the amplitude of the residual quenching stress have been determined for a family of Co-rich glass-coated microwires.

Investigation of the magnetostriction coefficient of amorphous ferromagnetic glass coated microwires

We measured the magnetostriction coefficient using small angle magnetization rotation method in amorphous ferromagnetic glass-coated Fe, Co, FeCo, and FeCoNi-based microwires. It was found that when the metallic nucleus of the microwire has a high magnetostriction—of the order (10–30) × 10−6 for FeCo-based microwires, the changing of diameters ratio, and hence, the magnitude and distribution of mechanical stresses have no significant effect on the value of the magnetostriction coefficient. In the case of nearly zero magnetostrictive FeCoNi-based microwires, increasing of the ρ−ratio leads to decreasing in the absolute value of the magnetostriction coefficient.

Correlation between the magnetostriction constant and thermal properties of soft magnetic microwires

We studied magnetic and thermal properties of Fe‐ and Co‐based glass‐coated microwires. The change of the specific heat near the Curie point, ΔCp, has been evaluated from the temperature dependence of the heat capacity obtained by the ratio‐method with sapphire as the reference. The values of the magnetostriction constant were measured for all prepared samples by using the small angle magnetization rotation method. We observed the correlation between the change of heat capacity at TC, ΔCp, and the magnetostriction constant, λs.

Correlation between thermal and magnetic properties of glass coated microwires

We studied magnetic and thermal properties of Fe and Co based glass coated microwires. We evaluated the magnetostriction constant of all prepared samples using the small angle magnetization rotation method. We observed the correlation between the change of heat capacity in TC, ΔCp, and the magnetostriction constant. We observed considerable change of Curie temperature and improvement of the GMI effect after annealing of Fe-rich Finemet-type microwires. Nanocrystallization of Fe-rich Finemet-type microwires results in magnetic softening.

Modified small angle magnetization rotation method in multilayer magnetic microwires

The small angle magnetization rotation (SAMR) technique is a widely used method to quantify magnetostriction in elongated ultrasoft magnetic materials. In the present work, we introduce significant optimization of the method, particularly simplification of the required equipment, profiting of the very peculiar characteristics of a recently introduced family of multilayer magnetic microwires consisting of a soft magnetic core, insulating intermediate layer and a hard magnetic outer layer. The introduced modified SAMR method is used not only to determine the saturation magnetostriction constant of the soft magnetic nucleus but also the magnetoelastic and magnetostatic coupling. This new method has a great potential in multifunctional sensor applications.

Magnetostriction of glass-coated Co-rich amorphous microwires and its dependence on current annealing

We present results on the saturation magnetostriction constant of four glass-covered Co-rich amorphous microwires for as-prepared and current annealed samples. The values of the saturation magnetostriction constant ( λ s) were obtained by using the small angle magnetization rotation method. The λ s data obtained in these magnetic materials are consistent with those previously reported in amorphous ribbons and wires with similar composition.

Positive and Negative Magnetostriction in Nearly Nonmagnetostrictive Amorphous Ribbons

It has been determined that nearly nonmagnetostrictive amorphous ribbons have two zones, the elongated and shortened regions of the ribbon, of roughly equal thickness, opposite signs of magnetostriction and different magnitudes. The bulk magnetostriction is approximately equal to the average magnetostriction value for the two zones. These results have been obtained using two different methods. One method involved the study of the dependence of the surface magnetization on the stress in two nearly nonmagnetostrictive amorphous ribbons in the as-quenched state as well as in those ribbons after different amounts of electrolytic polishing. The other method was based on the measurement of the magnetostriction coefficient in both the as-quenched and polished samples of the two ribbons by the small angle magnetization rotation method.

Effect of annealing on surface domain structure and magnetostriction of near zero magnetostrictive Co-rich wire

Investigations of magnetic reversal in a Co-rich amorphous wire were performed using the Kerr effect and small-angle magnetization rotation method. It was found that the sign of the magnetostriction was changed from negative to positive after current annealing. It is concluded that the outer shell of an as-quenched wire consists of circular bamboo domains, while an annealed wire displays axial maze domain structure.

Low temperature properties of nanocrystalline Fe 73.5Cu 1Nb 3Si 13.5B 9 ribbons

Many investigations on nanocrystalline samples were performed between room temperature and elevated temperatures but there is still a lack of low-temperature studies especially that of coercivity and magnetostriction. In this work we present measurements of the low-temperature behavior of magnetic properties like coercivity, magnetization and magnetostriction of Fe 73.5Cu 1Nb 3Si 13.5B 9 samples at different stages of crystallization and also in comparison to the amorphous state. The temperature dependence of the magnetostriction was measured by the small-angle magnetization rotation method which exhibits a high sensitivity. The magnetization data of the samples were used for analyzing the temperature dependence of magnetostriction in the low-temperature range in order to obtain information about the physical mechanism of the magnetostriction for such a kind of samples. From the temperature dependence of the magnetization, which follows the Bloch T 3/2 law, the spin wave stiffness constant can be estimated. The temperature dependence of coercivity H c below room temperature is also discussed.

Measurement of the magnetostriction constants of amorphous thin films on kapton substrates

The saturation magnetostriction constants of thin films of amorphous Co39Ni31Fe8Si8B14 and CoZrTb have been measured either by the small angle magnetization rotation (SAMR) method or by the initial susceptibility method. The SAMR method is used for the soft materials. When the material is magnetically hard or has a strong perpendicular anisotropy, the initial susceptibility method is used. It is found that the amorphous Co39Ni31Fe8Si8B14 prepared by ion beam deposition from an alloy target shows very soft magnetic properties and has a very small negative saturation magnetostriction, λs, of −1×10−7. Sputtered films of CoZrTb show a strong perpendicular anisotropy when the concentration of Tb is high. We have found that the SAMR method can be applied to CoZrTb films when the Tb content is low. The saturation magnetostricition constant of a sputtered film of Co78.4Zr20.8Tb0.8 is 2×106. When the Tb content is high, however, the initial susceptibility method is used to measure magnetostriction.

Saturation magnetostriction dependence on torsion in amorphous wire as measured by modified small angle magnetization rotation method

The small angle magnetization rotation (SAMR) method has been applied to the measurement of the torsional dependence of the saturation magnetostriction in a low-magnetostrictive amorphous Co-rich wire. The behaviour of the electric signal picked up from the sense coil has been investigated using experimental and numerical methods. The torsion introduces the first harmonic into the signal but the general formula for the measurement of the saturation magnetostriction remains valid. The conditions for the application of the method are discussed. The measurements of the saturation magnetostriction in the presence of an applied torsion have been carried out for as-quenched and annealed samples using different intensities of the annealing current. The magnetostriction coefficient, λs, depends linearly on the applied stress σ:λs = λs(0) + Aσ. The experimental dependence of the parameters λs(0) and A on the applied torsion and for different thermal treatments of the samples are also presented.

Evaluation of the linear magnetostriction in amorphous wires using the giant magneto-impedance effect

The stress dependence of the magneto-impedance effect is explored to estimate the magnetostriction constant and its stress derivative on a nearly non-magnetostrictive Co 68.1Fe 4.4Si 12.5B 15 amorphous wire. Comparing the results with those obtained with the small-angle magnetization rotation method, good accuracy is obtained.

Measurement of magnetostriction and induced magnetic anisotropy by SAMR method in Co-rich stress + field annealed amorphous ribbons

The saturation magnetostriction (λ s) and induced magnetic anisotropy ( K ind) in (Co 0.95Fe 0.05) 80Si 10B 10 annealed amorphous alloy ribbons have been measured at room temperature with the SAMR (small-angle magnetization rotation) method. The ribbons were annealed under simulataneous action of a stress and/or magnetic field. The variations of λ s and K ind show parallel trends in the cases of stress and stress+field annealings but not for single field annealing. These variations are connected with microstructural changes originated during the treatments.

Magnetostriction measurement of amorphous wires by means of small-angle magnetization rotation

The small-angle magnetization rotation method has been shown to be applicable for measuring the saturation magnetostriction of amorphous wires by using the circumferential field generated by an ac current through the wire. The method was used to measure compositional variation of magnetostriction of Fe-Co based amorphous wires. A saturation magnetostriction λs of 32.9×10−6 and −2.6×10−6 was found for Fe and Co based wires, respectively. The compositional variation of the saturation magnetostriction, λs, for (Fe1−xCox)75Si10B15 amorphous wires (X=0–0.8) decreases with increasing cobalt content and crosses zero around X=0.95 as in amorphous ribbons. The maximum experimental error of measurement was estimated to be about 5%.

Application of the SAMR method to high magnetostrictive samples

Magnetostriction measurement by using the small angle magnetization rotation method (SAMR) has been performed in high magnetostrictive amorphous samples. To apply the SAMR method to these samples, a theoritical model about the influence of the internal stresses and magnetization distribution has been proposed. The dependence of the magnetostriction, λ s, with the temperature and applied stress was measured in as-cast and in different annealed samples. In the as-cast samples the existence of a stray field and a dependence of λ s with the applied stress has been observed.