Study On The Effect Of Magnetic Field Heat Treatment On The Soft Magnetic Properties Of FeCo-based Amorphous Alloys

Amorphous and nanocrystalline soft magnetic alloys have attracted much attention due to their excellent soft magnetic properties such as low coercivity,high permeability,high saturation magnetic induction,and low core loss.Hence they have been extensively studied in recent years.Based on the exploration of the composition of amorphous and nanocrystalline alloys,it is also found that the magnetic field heat treatment can significantly improve their magnetic properties,but its effect on the properties and structure of the alloy still needs further exploration.Considering that the FeCoBSiNb alloy demonstrates excellent glass forming ability and mechanical properties,the Cu alloying effect and magnetic field heat treatment effect on magnetic properties of{[(Fe_0.5Co_0.5)_0.75B_0.2Si_0.05]_0.96Nb_0.04}_100-xCu_x alloys have been systematically investigated.The relationship between their structure and properties was also analyzed.First,based on the FeCoBSiNb alloy,different ratio of Fe to Co element was adjusted.Through the comparison of normal heat treatment and two-step longitudinal magnetic heat treatment,the effect of magnetic field heat treatment on the magnetic properties of amorphous alloys with different ratios of Fe to Co was studied.It is found that two-step heat treatment(Normal heat treatment+magnetic field heat treatment)can further effectively improve the magnetic properties of the alloy.Taking[(Fe_0.5Co_0.5)_0.75B_0.2Si_0.05]₉₆Nb₄ as an example,the coercivity H_c of the sample after two-step heat treatment was only 1/3 of the sample after the normal heat treatment at the same temperature,while the permeability?_e increased by 88%.At the same time,the saturation magnetic flux density B_s was also slightly increased.Then,the transmission electron microscopy found that some clusters were precipitated in the amorphous matrix of the sample after two-step heat treatment,which may be one of the reasons for the improvement of the magnetic properties.At the same time,the magnetic field heat treatment can suppress structural transformation to a certain extent.In addition,through the observation of the magneto-optical Kerr microscope,it is also found that the magnetic domains of the sample become wide and regular planar magnetic domains after the two-step heat treatment,thereby greatly enhancing the magnetic properties.Different content of Cu element was added on the basis of FeCoBSiNb alloy system to study the changes of magnetic properties of these alloys after the above two heat treatments.It was found that adding Cu element can further improve the magnetic properties of the sample.Similarly,the two-step heat treatment can greatly enhance the magnetic properties of the alloy,and it performs best when the Cu content is 0.4 at.%,so that{[(Fe_0.5Co_0.5)_0.75B_0.2Si_0.05]_0.96Nb_0.04}_99.6Cu_0.4 amorphous soft magnetic alloy ribbon sample with excellent magnetic properties has been prepared,its coercivity is as low as 0.27 A/m,and the effective permeability at 1 k Hz is as high as 29600.The changes in the microstructure were analyzed by transmission electron microscopy and magneto-optical Kerr microscopy,and it was found that the cluster precipitation and structural transformation were better after adding Cu element.There were some translational symmetric clusters observed.Besides,the magnetic domain width further increased,exceeding 300?m,which is the reason for the further improvement of its magnetic properties.Finally,the effect of transverse magnetic heat treatment on the coercivity,permeability,core loss and DC superposition properties of FeCoBSiNb amorphous alloys was studied,and it was found that the two-step transverse magnetic heat treatment can effectively reduce the coercivity and core loss of the sample,increase the permeability at high frequency,and the DC superposition properties were enhanced.The best applied magnetic field intensity and time of annealing in the two-step transverse magnetic heat treatment were obtained.Observed by a magneto-optical Kerr microscope,after the two-step transverse magnetic heat treatment,the magnetic domains of the sample became transverse planar magnetic domains,and the easy axis turns perpendicular to the ribbon direction.The magnetization mechanism is mainly the magnetic moment rotation.These factors together led to the changes in the above-mentioned magnetic properties.