Influence Of Magnetic Field Annealing On The Soft Magnetic Properties For The Dual-phase Nanocrystalline Alloys

The influence of lognitudinal magnetic field annealing on the soft magnetic properties for nanocrystalline Fe74.5Cu1Nb2Si22.5-xBx(x=5-13),(Fe0.5Co0.5)73.5Cu1Nb3Si13.5B9and Ni25(Feo.5Co0.5)48.5Cu1Nb3Si13.5B9alloys were intervestigated. The variations of saturation magnetostriction and effective magnetic anisotropy together with the initial permeability after magnetic field annealing for the dual-phase nanocrystalline alloys were mainly discussed.X-ray diffraction (XRD) showed that the dual-phase nanocrystalline structure with bcc a-Fe(Co,Ni)Si and residual amorphous phase was formed in the studied alloys after vacuum annealing at proper temperatures, the crystal phase volume fraction and the grain size changed with the annealing temperature and alloy composition. According to the μi～T curves, the Curie temperature of Fe-based, FeCo-based and NiFeCo-based amorphous alloys were detected as365℃,460℃and225℃, respectively, which offered the basis of magnetic annealing temperature.The evolution of saturation magnetostriction λs and effective magnetic anisotropy <K> after magnetic field annealing was observed to be different. The λs of nanocrystalline alloys decreased to varying degrees, which is due to the rearrangement of magnetic atoms along the applied field. Particularly, for620℃-annealed FeCo-basd nanocrystalline alloy, the value of λs dropped by84%after magnetic field annealing. However, the<K> of nanocrystalline alloys increased because of the induced uniaxial anisotropy, i.e., the<K> value of500℃-annealed FeCo-based nanocrystalline alloy increased by53%after field annealing, which is unfavorable for soft magnetic properties.As two key factors, saturation magnetostriction λs and effective anisotropy<K>, corretated with initial permeability μi, their variation remarkably affect the behavior of μi. In the present investigation, because the variation of λs and<K> was different in magnitude, the relative variation of<K> is usually larger than that of λs, so the changes of μi value is mainly controlled by the variation of<K>. Among the studied nanocrystalline alloys, the value of μi increased after magnetic field annealing only for the540℃-annealed Fe74.5Cu1Nb2Si17.5B5and620℃-annealed (Feo.5Coo.5)73.5Cu1Nb3Si13.5B9alloys, which is attributed to the greatly reduced magnetostriction. While for the other alloys, the μi decreased in different degree due to the increased effective magnetic anisotropy.