This is a new type of soft magnetic materials.

By melt-spinning method (roll method) obtained amorphous bands, such as they are heated to above the crystallization temperature to maintain a period of time (such a heat treatment called annealing), crystallization of amorphous bands will begin to , internal organizational changes from amorphous to crystalline state. If you control the annealing temperature and time properly, you can control the microstructure within the bands, making the crystallization of the grain size has been controlled in the range of 10 ~ 15nm, and that these grains are dispersed in the form distributed among the remaining amorphous phase, so that you can get nanocrystalline materials. For example, the composition of Fe73.5Cu1Nb3Si13.5B9 amorphous alloy annealed at 550 ℃ for 1 hour in the best magnetic properties of the state, the interior contains three-phase, one body-centered cubic structure of the FeSi phase, its composition of 20% Si and 80% Fe (atomic percent); not yet crystalline second phase is the residual amorphous phase, containing about 10% to 15% of Nb and B, the total volume of 20% to 30%; third phase is significant enrichment of Cu clusters. Adding a small amount of copper and niobium is to make these nanocrystals become the key to excellent soft magnetic materials. They are not dissolved in the body-centered cubic structure FeSi phase. However, Cu atoms form clusters in the early annealing, making it FeSi grain nucleation centers for the FeSi grain nucleation. Nb into the residual amorphous phase FeSi can prevent grain growth, while in the crystallization process, inhibiting the formation of Fe2B phase. If the annealing temperature higher than 600 ℃ Fe2B first phase will be formed, leading to overall deterioration in performance.

For nano-crystalline alloy, there is an exchange coupling length L0 = [A/K1] 1 / 2. Here, A is the exchange constant, K1 is a ferromagnetic alloy magnetic anisotropy constant phase. For the Fe-Cu-Nb-Si-B alloy, L0 = 35nm. When the grain size is less than L0, the magnetic moments of adjacent grains through the exchange interaction tends to be parallel. Therefore, the local anisotropy of the exchange coupling length of the response included within the scope of the average grain number of request, so the effective anisotropy constant of the material

<K> = K1 (D/L0) 6 = K14D6/A3.

Where, D is the size of nanocrystals. For the 20% Si-80% Fe alloy, K1 = 8 × 103J/m3, calculated from the above equation, the nanocrystals, the average anisotropy constant K1 <K> than about three orders of magnitude smaller, and only 0.5J / m3, thus reducing the material coercivity. As the Fe-Si grains and residual amorphous phase with the opposite sign of the magnetostriction coefficient (the former is negative, which is positive), so the two-phase alloys containing λs will be reduced, which can estimate permeability rate by one order of magnitude. This alloy is very thick domain wall, assuming that the residual amorphous magnetic anisotropy can be ignored, the domain wall thickness by the formula δ = π (A / <K>) 1 / 2 considered to 3μm, the domain wall thickness is much larger than grain size. As a result, the direction along the domain wall thickness, containing about 200 to 300 FeSi small grains. This, and the traditional materials on the contrary, it is this structure, although the grain size small as 10nm, but the two-phase interface is no longer likely to produce larger domain wall pinning effect. In addition, because the Fe-Si grain size is 10nm, while the interval between the grain and grain distance of 1 ~ 2nm, the residual amorphous phase volume fraction is low, they alloy the saturation magnetic flux density can still be up to 1.5 T, than the famous high permeability of permalloy (Ni79Fe21) and cobalt-based amorphous alloy is higher. For a thickness of 18μm bands, under the protection of inert gas at 550 ℃ annealing 1 hour, FeSi grain size of 13nm, corresponding soft magnetic properties as: μ1kHz = 100000, Bs = 1.24T, Hc = 0.5A / m , much lower than the loss of permalloy and cobalt-based amorphous same.

In recent years, such as nanocrystalline soft magnetic alloys, except alloy, has a new purpose. Because they have giant magneto-impedance effect, that is, when high-frequency current through the strip at the same time, such as along the strip before applying a DC magnetic field, the relative band impedance changes as high as 80% to 400%, and showing a high magnetic field sensitivity, therefore, become a very sensitive magnetic sensors excellent new material.

In addition to Fe73.5Cu1Nb3Si13.5B9, the nanocrystalline materials are also Fe-MC, Fe-MN (M = Ta, Hf, Ti, Nb, Zr) and Fe-MO (M = Zr, Hf) films. These materials were amorphous thin film by sputtering, then, to a certain temperature two-phase crystallization has been organized. One phase is the grain size of about 10nm body-centered cubic Fe-rich phase (bcc Fe), the other phase is the size of 1 ~ 3nm carbides (such as TaC), nitrides (such as ZrN) or oxide phase, They are distributed in the neighboring grain boundary intersection. As the carbides or nitrides of the grain size is less than the grain size of Fe-rich, Fe-rich magnetic coupling between grains is maintained; and because carbides or nitrides of the grain size is much smaller than the domain wall thickness, they do not will be pinning domain wall motion. Therefore, these thin films have good soft magnetic properties. Typically μ1MHz = 5000, Bs = 1.6 ~ 1.7T, λs = 10-7. Fe-MO (M = Zr, Hf) films in frequencies up to 100MHz is still high permeability, a typical performance μ100MHz = 2000, Bs = 1.5T, λs = (1 ~ 3) × 10-6.