High-Temperature And High-Frequency Magnetic Properties Of FeCoSiBNbCu Nanocrystalline Alloys

The structural characteristics and magnetic properties were investigated for Co-substituted FINEMET type ((Fe_1-xCo_x)_78.4Si₉BB₉Nb_2.6Cu₁ (x=0.35, 0.5, 0.65) alloys and (Fe_0.5Co_0.5)(79.4-x)Si₉B₉BNb_2.6Cu_x (x=0.5, 1.0, 1.5) alloys after annealing at various temperatures. The dependence of high-temperature and high-frequency magnetic properties on Co content, Cu content and annealing temperature were mainly studied.XRD was used to analyse the microstructures. The results show that, Changing Co content, Cu content and annealing temperature have great inflence on microstructures. A two-phase nanocrystalline structure composed of the amorphous matrix and theα-FeCo(Si) nanocrystallites is obtained by annealing samples at different temperatures from 460℃to 640℃for 0.5 h. The grain size is about 16 nm when annealing temperature is 490℃. With annealing temperature increasing, the grain size gradually increased. Both Co content and annealing temperature have a great influence on the lattice parameter, indicating that the proportion between the Co content distributed in the crystalline phase and that in the residual amorphous phase depends on Co content and annealing temperature.The high-temperature soft magnetic properties are studied by means of the temperature evolution of initial permeability. The results show that, the Curie point of the amorphous phase of FINEMET type alloy is enhanced by the partial substitution of Fe by Co. Onμi ? T curves of as-quenched alloys, a characteristic Hopkinson peak is observed at the Curie point of the amorphous phase, but it vanishes onμi ? T curves of crystallized alloys. For crystallized alloys,μi decreases with the temperature increasing, while the decreasing rate decreases with the annealing temperature increasing. The improvement of the high-temperature soft magnetic properties can be ascribed to the exchange coupling penetration. The random magnetocrystalline anisotropy model and the exchange coupling penetration are used to analyze the reason of the improvement of the high-temperature soft magnetic properties.The permeabililty spectra are measured so as to investigate the high-frequency soft magnetic properties. It is shown that, by adding Co to FINEMET type alloy,μi decreases while f0 remarkably increases. The equaton of domain wall motion and the domain wall pinning mechanism are used to analyze the relationship between high-frequency soft magnetic properties and Co content.