Structure And High-Temperature Magnetic Properties Of Nanocrystalline (Fe_xCo_1-x)_73.5Cu₁M₃Si_13.5B₉ Alloys

The structure and magnetic properties of Co-contained FINEMET type (FexCo1-x)73.5Cu1M3Si13.5B9(x=0.5,1 ; M=Nb, Mo) alloys were investigated by nanocrystallization of amorphous alloy precursors at various temperatures. The effects of annealing temperature and the addition of Co, Mo on high-temperature magnetic properties have been mainly analysed.The XRD results indicate that annealing temperature and the addition of Co and Mo have obviously influences on microstructures. A two-phase nanocrystalline structure composed of the amorphous matrix and theα-FeCo(Si) nanocrystallites is obtained by annealing amorphous alloy precursors above crystallization temperature. With the annealing temperature increasing, the grain size and the volume fraction ofα-FeCo(Si) phase gradually increase, the thickness of the intergranular amorphous layer decreases.The high-temperature magnetic properties were studied by measuring the temperature dependence of initial permeabilityμi. The results show that partially substitution of Fe by Co in FINEMET type alloys decreases the crystallization temperature of the amorphous phase; the saturation magnetic induction and initial permeability at room temperature are dropped slightly. But the Curie point of the crystalline phase and the amorphous phase are obviously enhanced; theμi could keep stable up to 600℃and the high-temperature soft magnetic properties are markedly improved. It is observed that an evident Hopkinson peak appears at the Curie point of the amorphous phase on theμi ? T curves of as-quenched alloys, but it disappears after nanocrystallizaion, andμi decreases with the temperature increasing. The random magnetocrystalline anisotropy model is used to analyze the reason of the improvement of the high-temperature soft magnetic properties.The method of measuring the evolution of the initial permeability with temperature during heating-cooling cycles has been used to discuss the relationship between the high-temperature magnetic properties and the structure from room temperature to 750℃. It is a good method to describe the changes of the structure and the magnetic properties during the transformation from the amorphous phase to the nanocrystalline phase.