Search

In this work, the structural and magnetic properties of Tb3 (Fe28� xCox )V 1.0 (x¼ 0, 3, 6) compounds have been investigated. The structural characterization of compounds by X-ray powder diffraction is an evidence for a monoclinic Nd3(Fe, Ti)29-type structure (A2/m space group). The refined lattice parameters a and b (but not c) and the unit cell volume V, obtained from the XRD data by the Rietveld method, are found to decrease with increasing Co concentration. The unit cell parameters behavior has been attributed to the smaller Co atoms and a preferential substitution of Fe by Co. The anisotropy field (Ha) as well as critical field (Hcr) was measured using the singular point detection (SPD) technique from 5 to 300 K in a pulsed magnetic field of up to 30 T. At T¼ 5 K, a FOMP of type 2 was observed for all samples and persists at all temperatures up to 300 K. For sample x ¼0, Hcr¼ 10.6 and 2.0 T at 5 and 300 K, respectively, is equal to that reported earlier. The occurrence of canting angles between the magnetic sublattices during the magnetization process instead of high-order anisotropy contributions (at room temperature are usually negligible) has been considered to explain the survival of the FOMP at room temperature. The anisotropy and critical fields behave differently for samples with x¼ 0, 3 compared with x¼ 6. The observed behavior has been related to the fact that the Co substitution for Fe takes place with a preferential entrance in the inequivalent crystallographic sites of the 3:29 structure. The contribution of the Tb-sublattice in the Tb3(Fe, V)29 compound with uniaxial anisotropy has been scaled from the anisotropy field measured on a Y3(Fe, V)29 single crystal with easy plane

Several sets of steel samples, like cold-rolled low carbon steel with different rolling reductions and thermal aged Fe–1 wt% Cu alloys, are investigated with respect to magnetic parameters such as coercivity, remanence and shape of the hysteresis loop. Measurements are performed in a magnetic open system, which allows magnetic saturation of the material and in a magnetic closed system using ring or picture frame shaped samples. The results obtained for ring or picture frame shaped samples give a much better accuracy for determining the coercivity. The coercivity (remanence) of the cold-rolled carbon steel samples increases (decreases) systematically with the rolling reduction. The duration of the thermally aging procedure performed at 450 °C has nearly no influence on the coercivity value. However, if thermally aging is applied on a cold-rolled sample, the coercitivity decreases with increasing aging time.

The effect of Joule heating on the magnetic properties and microstructure was investigated in Fe 73 Al 5 Ga 2 P 11− x C 5 B 4 Si x ( x =1, 3) ribbons with a thickness of about 40 μm. It turns out that, in these alloys, the coercive field, the pinning field and the time dependence of the initial permeability decrease with increasing current density applied during a thermal treatment via Joule heating up to the occurrence of crystallization. At the as-cast state, the sample with x =3 exhibits better soft magnetic properties than those of the sample with x =1; however, after an optimum annealing, both alloys present similar magnetic properties. The temperature dependence of the resistivity shows clear two stages crystallization process for the Fe 73 Al 5 Ga 2 P 8 C 5 B 4 Si 3 alloy. The microstructural and magnetic inhomogeneities of the annealed Fe 73 Al 5 Ga 2 P 8 C 5 B 4 Si 3 alloy with lowest coercivity were investigated by means of a small-angle neutron scattering method. The improvement of the soft magnetic properties caused by Joule heating of materials is due to the internal stress relieve originated during the production of the ribbon and to the enlargement of the domain wall thickness, consequently the reduction of the anisotropy.

Joule heating technique was used to anneal Fe73Al5Ga2P11C5B4 alloys. Magnetic properties as function of current density were characterised by hysteresis loops. Time and temperature dependence of the resistivity and temperature dependence of the susceptibility were measured in order to study the crystallisation behaviour. The results indicate a nearly linear dependence of the onset of the crystallisation of this sample on the heating rate.

Magnetic properties and structural evolution of the melt-spun Fe 80 - x Si 20 Cr x and Fe 87.1 - x Si 12.9 Cr x with Cr concentration are investigated for the as-cast and annealed samples. The coercivity at 300 K of the as-cast alloys decreases and that of the annealed ones increases with Cr concentration. For both as-cast and annealed samples, the saturation magnetization and the magnetic ordering temperature decrease, although heat treatments cause an increase of these magnetic properties. We have explained the behavior of these concentration dependence based on the structural analysis. Low-Cr region displays a discontinuity in the coercivity curve of the annealed alloys, which can be attributed to the change of the short-range order to the transient long-range ordered state.

We investigated the structural and magnetic properties of the as-cast Fe 100−( x + y ) Si x Nb y (with 9.5⩽ x ⩽20 and 0.5⩽ y ⩽12) and Fe 78.5 Si 20 Ta 1.5 alloys by means of coercivity measurements and zero-field nuclear magnetic resonance (NMR) technique. The NMR spectra of these alloys present broad resonance lines at around 80 and 130 MHz. An increase in the local magnetic stiffness with increasing Nb content was found. These results are discussed based on previously reported results about the microstructure of the same specimen and coercivity measurements.

The effect of the addition of Nb in Fe–Si alloys was investigated by measuring the magnetic properties and investigating the microstructure. Nb enhances (about 10 times) the coercivity and changes the microstructure as well as the temperature dependence of the coercivity. There exists indication that Nb enters in the lattice.