Direct Current Joule Heating Research Articles

Correlation of electrical and magnetic properties of Co-rich amorphous ferromagnetic microwires after DC Joule heating treatment

The present work describes the investigation of electrical and magnetic properties of the glass-coated Co-rich amorphous ferromagnetic microwires, having typical metallic core diameters d = 13–20 μm and tailoring by the direct current Joule heating. During this treatment, a continuous monitoring of the microwire condition was carried out, measuring its resistance by means of a DC bridge circuit. The heating of the microwire sample was provided by a direct current in the range from 20 mA to 63 mA. In this heating currents range, the microwires show a slight change in their resistivity. After annealing the resistivity of microwires may increase of about 1% with respect to as-prepared one. Depends on the heating current, the hysteresis loops of annealed microwires demonstrated the transition from a quasi linear type to a bistable one and vice versa. The maximum of the giant magnetic impedance ratio was observed in such microwires, which had a hysteresis loops describable by a near-zero anisotropy field.

Magnetoresistance of the Fe 72Cu 1V 3Si 16B 8 amorphous alloy annealed by direct current Joule heating

The longitudinal magnetoresistance of the Fe 72Cu 1V 3Si 16B 8 melt spun ribbon in its as-cast and nanocrystalline state has been studied. Successive thermal treatments with increasing in current intensity from 33 to 43 A/mm 2 were applied for a fixed time ( t an=180 s) in order to evolve nanocrystalline structure. Nanocrystals are detected by X-ray diffraction after treatment around 760 K. The volumetric fraction of the crystalline phase was calculated from the effective resistivity of the sample and by enthalpy data. The increases of α-Fe(Si) crystallites over 38% with residual amorphous matrix lead to the sign change from positive to negative magnetoresistance. The saturation in concentration of silicon in precipitated α-Fe crystallites to the value of 19 at % Si has been observed.

Mechanical behavior of nanocrystalline Fe–Hf–B ribbons

Investigation of annealing type (furnace annealing, direct current (DC) Joule heating, furnace pre-annealing followed by DC Joule heating) influence on the mechanical behavior (brittleness) of Fe–Hf–B nanocrystalline ribbons is presented. The results show a win of two orders of magnitude in terms of brittleness for furnace pre-annealing followed by DC Joule heating with respect to furnace annealing or DC Joule heating.

Crystallization of the Fe-Cu-M-Si-B (M=Nb, V) amorphous alloys by direct-current Joule heating

The effects of dc Joule heating on structural, electrical and magnetic properties of Fe-Cu-M-Si-B (M=Nb, V) amorphous alloys have been investigated. Amorphous ribbons of these two systems were resistively heated by direct currents from 1.5 to 2.5 A. X-ray diffraction analysis has shown that changes in the relative electrical resistance correlate with the onset of the crystallization process. The F shape of hysteresis loops indicates the induction of transverse magnetic anisotropy as a result of applied treatments.

Giant magnetoresistance in magnetic granular Co 15Cu 85 alloys annealed by direct-current Joule heating

We have studied the structure and giant magnetoresistance (GMR) in the Co 15Cu 85 granular alloys prepared by melt-spinning and annealed by the direct-current (dc) Joule heating. At T = 10 K, GMR as large as 50.0% (in a magnetic field up to 30 kOe) has been observed in a sample annealed with I = 6 A. The Joule-heated samples show higher GMR than those annealed by the conventional method. It is attributed to less content of residual Co in the Cu matrix for the dc Joule-heated samples than that for the samples annealed in a furnace.

Magnetic properties and giant magnetoresistance of magnetic granular Co10Cu90 alloys obtained by direct-current joule heating

The direct-current (dc) joule heating technique was exploited to fabricate giant magnetoresistance (GMR) Co10Cu90 granular alloys. The Co cluster precipitation process was investigated by calorimetric and x-ray diffraction measurements. At T=10 K, the largest MR change of 25.0% has been observed for the melt-spun Co10Cu90 ribbon annealed at I=5 A. The magnetoresistance scales approximately as the inverse Co particle size. At room temperature, it was found that the dc joule-heated samples show relatively high GMR in comparison with furnace-annealed samples. Based on the phenomenological GMR model, we assumed that it is a consequence of smaller Co particles formed in dc joule-heated samples.

Improved giant magnetoresistance in magnetic granular Co5 Cu95 alloys by direct-current joule heating

Improved giant magnetoresistance in magnetic granular Co5 Cu95 alloys by direct-current joule heating

Improved giant magnetoresistance in magnetic granular Co5 Cu95 alloys by direct-current joule heating

The dc joule heating technique has been used to produce giant magnetoresistance (GMR) Co5Cu95 granular alloys. At T=10 K, GMR as large as 28.5% has been observed in the as-quenched sample annealed with I=6A in a magnetic field up to 30 kOe. At room temperature, the joule-heated samples show higher GMR in comparison with that annealed by the conventional method.

Nanocrystalline Fe73.5 Cu1Nb3Si13.5B9 obtained by direct-current Joule heating. Magnetic and mechanical properties

Nanocrystalline ferromagnetic materials obtained by proper annealing of amorphous ribbons display excellent soft magnetic properties. However, the technological application of these nanostructured ferromagnets is hindered by their high brittleness. Direct-current Joule heating in vacuo is exploited to increase both the magnetic permeability and the ductility of nanocrystalline Fe73.5Cu1Nb3Si13.5B9. The development of the nanostructure in samples submitted to different Joule-heating currents for the same time (t = 60 s) has been analysed by means of X-ray diffraction, and is associated with magnetic permeability and reduced fracture strain measurements. Measurements of electrical resistance performed in the course of the heat treatment allows us to single out an activated process of atomic rearrangement occurring in the amorphous phase. Fracture strain data show that the alloy's embrittlement is mainly to be ascribed to this process rather than to nanocrystallization. It is shown that further improvement in the alloy's ductility can be obtained by inducing fast nanocrystallization in samples submitted to high electrical currents

Improved ductility of nanocrystalline Fe73.5Nb3Cu1Si13.5B9 obtained by direct-current joule heating

Direct-current joule heating is exploited to reduce the brittleness of ferromagnetic Fe73.5Nb3Cu1S13.5B9 nanocrystallized from the amorphous state. An ordering process occurring before nanocrystallization is singled out and shown to be responsible for sample embrittlement and magnetic-permeability degradation. The process is partially avoided by properly choosing the heating conditions. Nanocrystalline ribbon strips having substantially higher ductility than furnace-annealed samples, and maintaining excellent soft magnetic properties, are easily obtained.

Effects of deposition parameters on the synthesis of Nb 3Ge in the CVD process

The effects of deposition parameters on the synthesis of Nb 3Ge in the chemical vapour deposition process have been studied. The chlorides, NbCl 5 and GeCl 4, prepared by in situ chlorination were used. The Nb-Ge film was deposited on a Hastelloy-X tape which moved through a tubular reaction furnace and was heated by direct current Joule heating. Film deposition was carried out under carefully controlled conditions; in particular, temperature distribution of the reactive gas along its flow and that of the substrate tape in the longitudinal direction were accurately controlled. Most of the films prepared were composed of A15 Nb 3Ge compound with a small quantity of hexagonal and/or tetragonal Nb 5Ge 3 phases. Those films showed onset T c of ≈20 K. Uniform films in layer thickness, compound compositions, and superconducting critical temperature were obtained with good reproducibility by precise control of the deposition parameters.