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A study was conducted to determine circumferential magnetization curves for low, negative magnetostriction cobalt-rich amorphous wires supporting nominal composition under tensile stress using the magnetoimpedance effect. Frequency measurements were carried out in the 5 Hz-13 MHz range to determine spin rotation, domain wall bulging and wall displacement. Results indicated the damping of reversible magnetization processes by tensile stress.

The effects of thermal annealing on the frequency behavior of the initial permeability of vitrovac amorphous ribbons were investigated. The results showed that annealing temperatures above the Curie point resulted in a large increase in the magnetization dynamics of the material. However, it also caused a decrease in the domain wall relaxation frequency. The relaxation frequency was proportional to the degree of pinning while permeability depended on the inverse.

The complex circular permeability (mu(sub circ)) in a domain model for the magnetoimpedence (MI) of soft ferromagnetic wires is calculated using the complex inductance formalism (L). The results show that the L is an alternative approach to MI phenomena in soft ferromagnetic wires.

The complex inductance response and the giant magnetoimpedence effect of as-cast CoFeBSiMoNi microwires as a function of frequency and circular field amplitude is examined. The reduced dimension of the microwire indicates higher relaxation frequencies of 3 - 5 * 10(super 6) Hz and larger unpinning field of 127 A/m.

A detailed study of the complex inductance response of as-cast CoFeBSi wires as function of frequency (100 Hz-13 MHz range) and circular field amplitude [0.1-17A/m room mean square (rms) on the surface of the wire] in the giant magnetoimpedance arrangement is presented. In addition, a detailed analysis of real and imaginary parts of inductance leads to a characterization of the involved magnetization processes.

The dynamics of pinned domain walls is described by an equation of motion whose displacement term represents wall bulging. The equation is not capable of describing domain wall displacement in real materials as the bulging and threshold fields are highly complex. The equation of motion for bulging mechanisms is consistent with the method of equivalent circuits.

The F-thermal annealing method was applied to nanocrystalline amorphous Vitrovac 6025 metallic alloy samples in the temperature range 576 to 716 K for 10 to 90 minutes. The domain wall relaxation frequency and initial magnetic permeability were estimated and expressed on the basis of free wall surface area between the pinning sites and the dependence of wall bulging on anisotropy. The crystalline size up to 60 minutes annealing time was measured by transmission election microscopy.

A study of the magnetization process of Co-based amorphous ribbons at low frequencies as a function of decreasing thickness attained by chemical etching was discussed. The results suggested a decreasing tendency of magnetization effect with reduced thickness, while the relaxation frequency exhibited an inverse increasing trend domain-wall free-bulging area.

Coercivity enhancement of REFeAl bulk amorphous alloys was observed upon small B, Cu+B and Dy addition. Results can be attributed to both the existence of small crystallites in the substituted alloys, as well as the presence of RE, REFeAl clusters.

Presents a study on the effects of grain size distribution on the magnetization curve of polycrystalline ferrimagnets. Background on grain size distribution; Steps and equations necessary for the prediction of magnetization; Discussion on the Gobus model for magnetization mechanisms in polycrystalline ferrites.

Investigation of the domain wall permeability limit for the giant magnetoimpedance effect is discussed. The real part of the permeability is highly reduced at the relaxation frequency and gives rise to a decrease of the inductance while the imaginary part contributes to the resistance with maximum at the same frequency.

Magnetite nanoparticles about 10 nm sized were synthesized by the polyol method. Zero-field-cooled (ZFC)-FC measurements showed a blocking temperature ~170K and the absence of the Verwey transition. They were subsequently consolidated by spark plasma sintering at 750 °C for 15 min, leading to a high density (92% of the theoretical density), solid body, with grains in the 150 nm range. X-ray diffraction patterns exhibited a spinel single phase with cell parameters corresponding to the magnetite structure. Magnetic measurements showed a decrease of coercivity from 685 Oe (54.5 kA/m) at 118K to 90 Oe (7.2 kA/m) at 139 K. ZFC measurements at 25 Oe presented a three-fold magnetization increase as temperature increased; a small transition between 116 and 117.5 K, followed by a larger one from 117.6 to 124 K. The first transition can be associated with a complex crystallographic transition and delocalization of Fe2+-Fe3+, while the second one can be attributed to spin reorientation due to the magnetocrystalline anisotropy constant (K1) change of sign as previously observed only in magnetite single crystals. [ABSTRACT FROM AUTHOR]

Complex inductance formalism (L) is used to calculate the complex circular permeability (μ[SUBcirc) in a domain model for the magnetoimpedance (MI) of soft ferromagnetic wires. An excellent agreement between calculated and experimental values of μ[SUBcirc] as a function of frequency is observed. In addition, a very good agreement is also exhibited between experimental and calculated plots of μ[SUBcirc] as a function of an applied dc magnetic field before and above the relaxation frequency (also known as single- and double-peak MI effect). These results confirm the validity of L as an alternative approach to MI phenomena in soft ferromagnetic wires. [ABSTRACT FROM AUTHOR]

The magnetoimpedance (MI) effect is based on the change of inductance and resistance under the effect of an external magnetic field. In bulk homogeneous wires or ribbons these two components of the impedance are related to the penetration depth of the electromagnetic field in the material. From simple considerations it is shown that the maximum MI ratio is then proportional to the square root of the relative permeability of the material. That limit is reached for frequencies at which the penetration depth is of the order of the transverse dimensions of the sample. At low operating frequencies, typical of thick geometries, the permeability is limited by the microeddy currents associated with domain wall displacements. The permeability relaxation equivalent to these local eddy currents can be calculated and used in the classical expressions for MI. The real part of the permeability is highly reduced at the relaxation frequency and gives rise to a decrease of the inductance, while the imaginary part contributes to the resistance, with a maximum at the same frequency. [ABSTRACT FROM AUTHOR]

Impedance spectroscopy measurements were carried out on amorphous ribbons of nominal compositions Fe[sub 93-x-y]Zr[sub 7]B[sub x]Cu[sub y] (x=6,8 and y=0,1,2), in the frequency range of 5 Hz–13 MHz. Two different geometries were used for measurements: a longitudinal one by using an 80-turn solenoid and the magnetoimpedance geometry, where the ac current flows through the ribbon itself. The obtained results showed a larger initial permeability value for longitudinal domain walls, as compared with transverse ones. Results concerning the propagation field showed the opposite behavior. These results are interpreted in terms of the short-range order arrangements of Fe atoms in these alloys, also known as “nanoamorphous demixing structures.” © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the measurements of monodomain, polycystalline hexagonal ferrites and amorphous ribbons. Information on the magnetization mechanism at low measuring frequencies in polycrystalline ferrites; Details on the experimental techniques; Experimental results.

Focuses on a study which extended the domain wall size model of polycrystalline ferrimagnetics to the case of ferromagnetic amorphous ribbons. Role played by surface pinning; Assumption on the function of magnetization; Focus of the function of the domain wall size model; Mechanisms proposed to account for pinning phenomena in amorphous ribbons.

Presents information on a study which showed that the thermal dependence of the critical magnetic field can be given in terms of the saturation magnetization and the initial magnetic permeability. Experimental procedure; Results and discussion.

Studies the temperature dependence of the critical magnetic field in Vitrovac-type magnetic amorphous ribbons. Use of polycrystalline nickel ferrite; General behavior of the critical fields as a function of temperature; Effect of nucleation and crystallization phenomena on the high-temperature behavior of the critical field.

Presents an abstract of the article 'Influence of the Grain Size Distribution on the Ferromagnetic Hysteresis Loop,' by M.A. Escobar, L.F. Magana and R. Valenzuela.