Anisotropy field-annealing induced

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. 

It should be noted that annealing treatments in a magnetic field of specified direction induce atomic rearrangements which provide an additional anisotropy termed uniaxial anisotropy K. It can be used to modify the field dependence of magnetic induction in such a way that the hysteresis loop takes drastically different forms, as shown in Fig. 4.3-13. 

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