Abstract
The soft magnetic behaviors at elevated temperatures for magnetic field annealed nanocrystalline Fe73.5Cu1Nb3Si13.5B9, (Fe0.5Co0.5)73.5Cu1Nb3Si13.5B9 and Ni10(Fe0.5Co0.5)63.5Cu1Nb3Si13.5B9 alloys were investigated by the temperature evolution of initial permeability (μi-T curve). The results show that magnetic field annealing gives rise to a persistent increasing μi from room temperature to a relatively higher temperature for Co- and NiCo-containing Finemet. Especially for the magnetic field annealed NiCo-containing Finemet, the μi is evidently improved in the temperature range between 200-600°C with respect to the sample without magnetic field annealing.
Highlights
The soft magnetic performance at high temperature arises from the presence of intergranular magnetic coupling between adjacent nanocrystals through the residual amorphous phase,4 and this coupling depends both on the size of nanocrystallites and more importantly on the amount, chemistry, thickness and in particular the Curie temperature of the intervening amorphous phase
The decoupling of the ferromagnetic grains occurs when the operating temperature is close to the Curie temperature of residual amorphous matrix, leading to the deterioration of magnetic softness for most nanocrystalline alloys
The previous reports on magnetic field annealing mainly focus on the improved magnetic softness at ambient temperatures,12,13 and hardly pays attention to the evolution of exchange-coupling interaction between nano-sized grains by magnetic field annealing for nanocrystalline soft magnetic alloys
Summary
The investigation on nanostructured soft magnetic materials represents a topic of growing interest in the field of dualphase nanocrystalline alloys for high-temperature application. The soft magnetic performance at high temperature arises from the presence of intergranular magnetic coupling between adjacent nanocrystals through the residual amorphous phase, and this coupling depends both on the size of nanocrystallites and more importantly on the amount, chemistry, thickness and in particular the Curie temperature of the intervening amorphous phase. the decoupling of the ferromagnetic grains occurs when the operating temperature is close to the Curie temperature of residual amorphous matrix, leading to the deterioration of magnetic softness for most nanocrystalline alloys. In the previous works, improvements in intergranular exchange coupling have been explored by variations in the magnetic metal composition of the alloys, the effective remedy is the addition of cobalt to Finemet- and Nanoperm-type alloys. It has been identified that partial substituting Fe by Co in Finemet-type alloy can enhance the exchange correlation length and increasing the volume fraction of crystallites can reduce the thickness of amorphous phase in the nanocomposite, both of which can suppress the decoupling of grains at elevated temperatures. The soft magnetic performance at high temperature arises from the presence of intergranular magnetic coupling between adjacent nanocrystals through the residual amorphous phase, and this coupling depends both on the size of nanocrystallites and more importantly on the amount, chemistry, thickness and in particular the Curie temperature of the intervening amorphous phase.. The decoupling of the ferromagnetic grains occurs when the operating temperature is close to the Curie temperature of residual amorphous matrix, leading to the deterioration of magnetic softness for most nanocrystalline alloys.. The previous reports on magnetic field annealing mainly focus on the improved magnetic softness at ambient temperatures, and hardly pays attention to the evolution of exchange-coupling interaction between nano-sized grains by magnetic field annealing for nanocrystalline soft magnetic alloys. The observed temperature evolution of μi is analyzed within the framework of magnetic exchange-coupling interaction between the ferromagnetic grains
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