Showing papers by "Marcelo Knobel published in 1994"
TL;DR: In this paper, the advantages of this rapid heating technique are highlighted, and the average grain size of Joule-heated samples is significantly lower than in the furnace-annealed alloy.
63 citations
02 May 1994
TL;DR: In this paper, the effect of the initial degree of topological disorder on the formation of the nanocrystalline state, two amorphous ribbons of composition Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 produced in different laboratories were investigated.
Abstract: In order to study the effect of the initial degree of topological disorder on the formation of the nanocrystalline state, two amorphous ribbons of composition Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 produced in different laboratories were investigated. Measurements of hysteresis loops, disaccommodation and magnetostriction were performed on as-cast and nanocrystalline samples. An analytically solvable model describing the stress dependence of the coecivity is discussed. Two types of analysis of the approach to saturation are used to estimate the distribution function of the magnetization vectors. From the pinning field, the dimension of long-range order stresses in the nanocrystalline state is deduced.
26 citations
01 May 1994-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a general solution of the equation describing the evolution of the sample temperature and resistance in the course of d.c. joule heating is found, and the role of the transfer rate of the crystallization heat to the sample is briefly discussed.
Abstract: A d.c. joule heating technique allows new application-oriented crystallization products to be obtained from amorphous metallic ribbons under controlled conditions. The structural changes occurring in a material are continuously monitored through on-line measurements of the electrical resistance. Sample crystallization is often marked by a typical resistance bump. A general solution of the equation describing the evolution of the sample temperature and resistance in the course of d.c. Joule heating is found. The crystallization of Fe 40 Ni 40 B 20 , characterized by a strong emission of heat, is treated in detail. Specific parameters of the process are properly determined from a comparison with experimental results. The role of the transfer rate of the crystallization heat to the sample is briefly discussed.
21 citations
TL;DR: In this paper, a system for magnetic characterization of soft magnetic materials in low field is described, which allows to perform permeability, pinning field, Curie temperature and disaccommodation measurements automatically.
Abstract: A system for magnetic characterization of soft magnetic materials in low field is described. Fields of 0.02 A/m can be applied and a good sensibility is achieved by means of a Lock-In amplifier. Signals of 1 nV can be measured, and magnetic characterization with external stresses can be made. The measurements can be done from room temperature up to 973 K. The system allows to perform permeability, pinning field, Curie temperature and disaccommodation measurements automatically. >
9 citations
TL;DR: In this paper, the electrical resistance in the course of fast Joule heating displays distinctive features during the development of the nanocrystalline phase, which are explained using a recently developed theoretical model.
Abstract: Amorphous Fe/sub 73.5/Nb/sub 3/Cu/sub 1/Si/sub 13.5/B/sub 9/ ribbons were submitted to fast direct current (dc) Joule-heating treatment in vacuum. The electrical resistance in the course of fast Joule heating displays distinctive features during the development of the nanocrystalline phase, which are explained using a recently developed theoretical model. The experimental parameters of the current annealing were optimized in order to obtain ductile soft magnetic materials using very high heating rates. >
8 citations
TL;DR: In this article, low-field initial permeability (μ i ) has been measured at several steps of nanocrystallization in four amorphous Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 ribbons produced by planar flow casting with different quenching rates (QRs) from the melt.
7 citations
TL;DR: In this article, the electrical resistance of four Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 13.5 /B/sub 9/ ribbons obtained by melt spinning with different quenching rates were submitted to direct current (DC) Joule heating treatment in vacuum.
Abstract: Four Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 13.5/B/sub 9/ ribbons obtained by melt spinning with different quenching rates were submitted to direct current (DC) Joule-heating treatment in vacuum. On-line measurements of the electrical resistance were performed in the course of Joule heating in order to study the development of the nanocrystalline phase. The results show that the nanocrystallization kinetics is strongly dependent on the initial degree of structural disorder. The increase in both initial magnetic permeability and brittleness upon nanocrystallization were observed to be affected by the initial topological disorder. >
6 citations
TL;DR: In this paper, the after-effect scales roughly with the square of the magnetostriction constant and the concentration dependence of the pinning field can be correlated with that of the coercivity.
4 citations
TL;DR: In this article, a negative giant magnetoresistance (GMR) was reported in a bulk granular Cu90Co10 system with melt-spun ribbons to conventional annealing and dc joule heating in order to induce diverse microstructures.
Abstract: Bulk granular Cu90Co10 systems displaying a negative giant magnetoresistance (GMR) were produced by submitting melt‐spun ribbons to conventional annealing and dc joule heating in order to induce diverse microstructures. Room‐temperature GMR values up to 9% at 20 kOe were found in samples produced using both kinds of thermal treatments. An evolution from a superparamagnetic towards a ferromagnetic behavior has been observed in samples submitted to different heat treatments. A long‐time, nearly logarithmic relaxation of the magnetic remanence has been measured after fast removal of a magnetic field of 10 kOe. The progressive randomization of the magnetic moments also gives rise to a corresponding increase in the zero‐field electrical resistance.
3 citations