Field annealing

Different field-annealing effects on the magnetostriction are evident across the whole composition range, as summarised in fig. 19. For the Co-rich alloys, b increases... 

It is well known that the substitution of Dy for Tb gives rise to an increase of the magnetostriction at low magnetic fields, through the reduction of the saturation field. It is, however, also accompanied by a reduction of the saturation magnetostriction. The Co substitution in the R-(Fe,Co) alloys, in combination with the effects of field annealing,... 

Fig. 41. Magnetostriction loops (parallel and perpendicular measurement direction) of an as-deposited (open symbols) and a magnetic-field annealed Tbo.4Feo.6(7 nm)/Feo 5C00 5(9 nm) multilayer (closed symbols) ...

A systematic study by Herzer [44] on the effect of Si content on the field induced Ku in the nanocrystalline Fe-Si-B-Nb-Cu alloys indicated that Ku is mainly induced in the crystallites. By appropriate choice of alloy composition and annealing conditions, transverse field annealing of nanocrystalline Fe-Si-B-Nb-Cu alloys allows to induce anisotropies in the range of Au 5 - 100 J/m3. This corresponds to initial permeabilities of about fii 104 - 2 x 105. They perfectly cover the needs of applications like common mode chokes or earth leakage circuit breakers [45] which require high permeabilities. 

In the Ni-Fe system at room temperature, the a phase extends from 0 to 7% Ni, then a. Fy mixtures from 7 to 50% Ni, and the y phase from 50 to 100% Ni. y-Phase alloys in the Ni-Fe system, known as Permalloys, exhibit a wide variety of magnetic properties, which may be controlled precisely by means of well-established technologies. Initial permeabilities up to 10 in an extremely wide temperature range, as well as coercive fields between 0.16 and 800 A/m, can be obtained (Chin Wemick, 1980). Induced anisotropy of 65-85% Ni alloys can be drastically varied by field annealing and mechanical deformation (slip-induced anisotropy) an order-disorder transformation occurs for Ni3Fe finally, preferential orientation can be induced in 50%Ni-50%Fe. 

Combined with small alloy variations, primary treatments and field annealing treatments, a wide variety of annealed states can be realized to vary the induction behavior. The field dependence of the permeability of some high-permeability Ni—Fe alloys (designations according to Vacuumschmelze GmbH) are shown in Fig. 4.3-14 [3.16]. 

The saturation polarization ranging from 0.55 to LOT is lower than in Fe-rich amorphous alloys but comparable to the 80 wt% Ni crystalline permalloy materials. By applying magnetic field annealing, weU-controlled Z-type and F-type loops can be realized. 

Table 4.3-24 shows the magnetic and physical properties of some commercially-available nanocrystalline alloys for conqtarison to amorphous and Ni—Fe-based crystalline soft magnetic alloys. Magnetic field annealing allows the shape of the hysteresis loops of... 

Pang H, Chen C, Zhang Y-C, Ren P-G, Yan D-X, Li Z-M (2011) The effect of electric field, annealing temperature and filler loading on the percolation threshold of polystyrene containing caibon nanotubes and graphene nanosheets. Carbon 49 1980... 

In principle, all of the parameters in this equation are measurable so it should be possible to determine the mobility from the voltage dependence of the current. However, the actual behaviour of cells of this type is critically dependent on the nature of the interface. The currents obtained can also depend on the history of the cell. One example of this and of another way that ppm levels of ionic impurities can cause problems is provided by the field anneal phenomenon [25, 26]. If the sample is heated into the isotropic phase and a DC current applied to the cell for a period of time ionic impurities become adsorbed on the electrode surface where they help to facilitate charge injection. Thereafter the I/V characteristics of the Col phase are found to be totally different and, in extreme cases, the measured conductivity can (apparently) be orders of magnitude higher Because of the extreme sensitivity of sandwich cell measurements to small difference in the electrode surface and, because experimentally the voltage dependence of the current often deviates quite markedly from the expected (V-Vc) behaviour, reliable determination of mobilities from the I/V curves is difficult and this approach is rarely used [27]. 

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