Structure And High Temperature Magnetic Properties Of Ge Dopped FeCo Based Nanocrystalline Alloys

The microstructure and high temperature soft magnetic properties of the(Fe_0.9Co_0.1)_73.5Si_13.5B_9-xNb₃Cu₁Ge_x?x=0,1,3?and(Fe_0.8Co_0.2)_73.5-xSi_17.5B₅Nb₃Cu₁Ge_x?x=0,0.5,1?nanocrystalline alloys were studied.The differential scanning calorimetry?DSC?was used to measure the crystallization temperature of as-quenched alloys;The microstructure of as-quenched and nanocrystalline alloys was analyzed by X ray diffraction?XRD?;The initial permeability??_i?and the Curie temperature?T_c^A?were obtained through a high temperature magnetic permeability measuring instrument made by laboratory.The effect of doping Ge on the microstructureandhightemperaturesoftmagneticpropertiesin(Fe_0.9Co_0.1)_73.5Si_13.5B_9-xNb₃Cu₁Ge_x?x=0,1,3?and(Fe_0.8Co_0.2)_73.5-xSi_17.5B₅Nb₃Cu₁Ge_x?x=0,0.5,1?alloys were investigated.The experimental results show that for(Fe_0.9Co_0.1)_73.5Si_13.5B_9-xNb₃Cu₁Ge_x?x=0,1,3?alloys,the substitution of Ge for B makes the Curie temperature of the amorphous alloy decrease.With the addition of Ge the initial crystallization temperature of the quenched alloy(T_x1)and the second crystallization temperature(T_x2)first rise and then decrease,the crystallization interval temperature?T_x(?T_x=T_x2-T_x1)gradually increases.The crystallization temperature interval of(Fe_0.9Co_0.1)_73.5Si_13.5B₆Nb₃Cu₁Ge₃is increased by 51?compared with that of Ge-free(Fe_0.9Co_0.1)_73.5Si_13.5B₉Nb₃Cu₁alloy.Successive heating-cooling cycle annealing of(Fe_0.9Co_0.1)_73.5Si_13.5B₆Nb₃Cu₁Ge₃samples revealed that the samples annealed at 600?exhibited the most excellent magnetic properties.The initial permeability can maintain the highest value at room-and high-temperatures.When the heating temperature reaches up to 550?,the initial permeability can still be above 1000?measured at 10 KHz?.The XRD results of the(Fe_0.9Co_0.1)_73.5Si_13.5B₆Nb₃Cu₁Ge₃ samples annealed at 500-650?show that the alloy annealed at 600?has a higher crystallization phase volume fraction(V_cry)and a thinner amorphous layer thickness???before precipitating the hard magnetic phase,and the exchange coupling effect between the grains is enhanced significantly.(Fe_0.8Co_0.2)_73.5-xSi_17.5B₅Nb₃Cu₁Ge_x?x=0,0.5,1?family alloys were obtained by doping a small amount of Ge into(Fe_0.8Co_0.2)_73.5Si_17.5B₅Nb₃Cu₁ alloy.By doping Ge the Curie temperature of the amorphous alloy gradually increased,the initial crystallization temperature gradually decreased,and the crystallization temperature interval increased.(Fe_0.8Co_0.2)_72.5Si_17.5B₅Nb₃Cu₁Ge₁ alloy exhibits the highest Curie temperature and the largest crystallization temperature interval.The heating-cooling cycles experiment of(Fe_0.8Co_0.2)_73.5-xSi_17.5B₅Nb₃Cu₁Ge_x?x=0,1?shows that the alloy has the best soft magnetic properties after annealing at 650?.So(Fe_0.8Co_0.2)_73.5-xSi_17.5B₅Nb₃Cu₁Ge_x?x=0,0.5,1?alloys were also annealed at 650?in vacuum and the change of initial permeability with temperature was measured.The?_i-T curve shows that(Fe_0.8Co_0.2)_72.5Si_17.5B₅Nb₃Cu₁Ge₁ alloy not only has the highest initial permeability?¹4000?at room temperature but also the permeability at elevated temperature is obviously improved compared with the other two alloys,and higher?_i of above 1000?measured at 10 KHz?can be kept up to 630?.