FeCo基纳米晶合金高温交换耦合作用机理

Mechanism of high-temperature exchange-coupling interaction of FeCo-based nanocrystalline alloy

研究了500和600℃真空退火后的纳米晶Fe38.4Co40Si9B9Nb2.6Cu合金初始磁导率随温度的变化规律,发现较高温度(600℃)退火的FeCo基纳米晶合金,在非晶相居里温度以上较宽温度范围内磁导率没有明显的衰减,这是在双相纳米晶合金中观察到的一种新现象,其磁特性不同于Fe基纳米晶合金.为了探明这种现象的起源,估算了与剩余非晶相同成分的非晶合金的居里温度及纳米晶粒间发生交换耦合作用的参数.结果显示,双相纳米晶合金晶粒间发生完全交换耦合穿透作用时,晶粒间非晶层的表观居里温度可大幅提高到与晶化相居里点相同的温度(即TcA=Tcα),并计算得到α-FeCo晶粒间发生完全交换耦合穿透作用的临界厚度(Λc)大于α-Fe晶粒的Λc,解释了高温下FeCo基纳米晶合金磁导率明显高于Fe基纳米晶合金的原因.

Temperature dependence of initial permeability is investigated for nanocrystalline Fe38.4 Co40 Si9B9Nb2.6 Cu alloy annealed at 500 and 600℃ ,and the initial permeability of 600℃-annealed sample is observed not to drop sharply at the Curie temperature of the residual amorphous phase,which is a new magnetic phenomenon in dual-phase nanocrystalline alloys.The origin of the above phenomenon is explored by estimating the Curie temperature of amorphous ribbons which have the same compositions with the residual amorphous phase in annealed nanocrystalline alloys.The results indicate that the Curie temperature of the intergranular amorphous region can be enhanced drastically up to the Curie temperature of the crystalline phase （TAC = TCα ） when the exchange-field between adjacent nanograins penetrates through the amorphous interphase thoroughly.Furthermore,the effective exchange penetration length of FeCo-based nanocrystalline alloys （LFeCo） is evaluated to be 0.61 nm much larger than that of Fe-based nanocrystalline alloys,which may be the main reason of the higher permeability of FeCo-based alloys at elevated temperature.