Nanocomposites and nanomaterials
Influence of thermomagnetic treatment on frequency magnetic properties of nanocrystalline Fe73Nb3Cu1B7Si16 cores 
Nosenko A.V., Mika T.M., Boshko O.I., Yevlash I.K., Semyrga O.M., 
Nosenko V.K.

G.V. Kurdyumov Institute for Metal Physics of National Academy of Sciences of Ukraine, 36, Academician Vernadsky Boulevard, Kyiv, 03142, Ukraine. 
E-mail: itrij@ukr.net 

The amorphous Fe73Nb3Cu1B7Si16 ribbon crystallized by heat treatment in an external magnetic field of 0.12T, applied across the ribbon axis (TMT). Thermal treatment of the Fe73Nb3Cu1B7Si16 alloy leads to the formation of Fe(Si) nanocrystals, which improves its magnetic properties. The volume fraction of nanocrystals in them is 75-80%, and their sizes are about 10nm. The attachment of an external magnetic field during annealing or cooling of the core results inducing in ribbon a uniaxial magnetic anisotropy. The magnitude of the induced magnetic anisotropy can be varied by the temperature at which the magnetic field is applied. It is shown that the magnetic anisotropy is easier to induce at temperatures near the Curie point of 6070C of α-Fe nanocrystals.
A comparison of the magnetic properties of the cores after convention annealing and TMT at a temperature of 3300С and 5800С was done. It was established that an increase in the temperature of the TMT (up to 5800C) core compared with the convention annealing leads to a decrease: the initial magnetic permeability (i1=170000  85000), the rectangularity coefficient (from 0.89 to 0.54) and core loss. In particular, for a frequency of 80kHz, a maximum magnetic induction of 0.2T, this reduction is 43W/kg (standard annealing 48W/kg). An increase in the temperature of the TMT (up to 5800C) increases the frequency stability of the initial magnetic permeability of the core.
In particular, for a frequency of 50kHz, it is 50000 (convention annealing of 26000). The advantage of the core of annealed in external magnetic field is the independence of the effective magnetic permeability of the core from the magnitude of the field up to the achievement of saturation induction.