Influence Of Flash Annealing By Pulsed Current On The Magnetic Properties Of NiFe/FeMn

Under the trend of the miniaturization and integration of the electrical and electronic equipments,ferromagnetic?FM?thin films,presenting excellent dynamic magnetic characteristic in GHz-band,gain popularity in the fields of anti-electromagnetic?AFM?interference,microwave absorption device and so on.The ferromagnetic resonance frequency of the ferromagnetic thin films can be further enhanced through regulating its magnetic anisotropy.This is always one of the important research directions in this field.The exchange biased film,based on the exchange coupling between ferromagnetic layer and the antiferromagnetic layer,have better adjustability due to the introduction of the new unidirectional anisotropy and rotational anisotropy.In this research,with the exchange biased[NiFe?15 nm?/FeMn?10 nm?]film as the object,the pulsed current was employed to fast anneal the film and the magnetic properties,particular the rotatable anisotropy and the ferromagnetic resonance frequency,of the annealed films were focused research.The main results of this research are listed below:1.The platform for pulsed current annealing of magnetic films was built successfully,including vacuum annealing furnace,DC electrical source and pulsed current generator.The base pressure of the vacuum annealing furnace is superior to 1×10^-4 Pa.The annealing time of the film can be controlled in the time range of<0.1 s,through the controlling of the parameters of the pulsed current annealing circuit.The annealing temperature of the film could be controlled in the range from room temperature to 1000??2.Through the accuracy control of the annealing parameters,the unsaturated magnetic reversal films were successfully prepared at 40⁴5 V critical annealing voltages in the reversed magnetic field.After annealing at these critical annealing voltages,the exchange bias filed and static anisotropic field reach their minimum,while the ferromagnetic resonance frequency reach their maximum.When we annealed the film using the critical annealing voltage,the temperature of the film instantly rised to the value high that the Néel temperature of the antiferromagnetic FeMn layer,and the AFM moments became disorder;in the process of cooling down,the AFM moments would have the tendency to turn to the applied magnetic field direction;after the film temperature below the Néel temperature of FeMn,only parts of the AFM moments achieved the turn while the others oriented at different directions due to the cooling down of the film is really fast;this is the reason for the smaller static anisotropic field and exchange bias filed,and the bigger rotatable anisotropy and ferromagnetic resonance frequency;further,it is because the augment of the unstable AFM grains?rotatable-spin grains?due to the competition of the moments with different directions.3.Through the combination of the pulsed current annealing method and the Ag lines annealing circuit,the film with anti-parallel exchange bias filed was successfully prepared,which exhibited two exchange bias fields with opposite direction and two ferromagnetic resonance frequencies.And the two exchange bias fields are all smaller than the unannealed sample,while the two ferromagnetic resonance frequencies are all bigger than that of the raw film.The highest ferromagnetic resonance frequencies could reach 5.61 GHz.The film regions have the negative exchange bias represented the exchange bias direction of these film regions are oriented to the deposition magnetic field direction,while the film regions have the positive exchange bias represented the exchange bias direction of these film regions are oriented to the applied magnetic field direction.4.The unstable AFM grains of the film with anti-parallel exchange bias filed increased due to the competition between the FM and AFM moments with different directions,which causes the strengthening of the rotatable anisotropy of the film,and further induces the enhancement of the ferromagnetic resonance frequency.It was found that the film regions with smaller exchange bias presented higher ferromagnetic resonance frequency,while the film regions with bigger exchange bias presented lower ferromagnetic resonance frequency.This may be because the film regions with smaller exchange bias is narrow,so under the competition of the ambilateral moments with opposite direction,the proportion of the unstable AFM grains in this region is very high and thus the rotatable anisotropy is large.