| Ll0FePt alloy is a promising candidate for the next generation of ultra high density magnetic storage medium due to its high uniaxial magnetocrystalline anisotropy energy, large saturated magnetization intensity and stable chemical properties, etc. However, the maximum magnetic field that can be abtained from the write head can’t make the recording unit made of L10FePt magnetization reversal. The ordered B2(a" phase) FeRh alloy undergo a magnetic transition from antiferromagnetic(AFM) to ferromagnetic(FM) behavior by heating above room temperature. The reversal field of recording unit may be reduced obviously by inserting a FeRh function layer above or below the recording layer using exchange spring in the FeRh/FePt composite film. In this thesis, the FeRh/FePt and FePt/FeRh bilayer film(the former film is the underlying layer) were prepared by magnetron sputtering on MgO(001) single crystal substrate. In order to explore the growth technology of exchange-coupled FePt/FeRh bilayer films, the structure, surface morphology, magnetization characteristic and thermal magnetic properties of the thin films were anylized by XRD, SEM and VSM, respectively. The main results are as follows:1. The Fe0.8Rh1.2thin film on the500℃substrate appear less ordered a" phase content and the paramagnetic y phase. After a vacuum annealing at temperature of600℃, the ordered a" phase content increase obviously, which indicate a higher degree of order of the film. Due to the slow diffusion of Rh atoms, the content of γ phase does not decrease. The annealed Fe0.8Rh1.2film exhibit a first-order magnetic phase transition between AFM and FM in the process of heating. The phase transition temperature Ttr depends on the size of the external magnetic field. With the increase of the external magnetic field. Ttr decrease. Fe1Rh1film annealed at450℃has begun to order and There is noγ phase diffraction peak in FeRh X-ray spectrum. Anneaed at600℃, the half high width of a" diffraction peak become narrow, which indicate that the degree of order of thin film has been improved. The peak position of a" moves to the right, which show that the length of c axis of FeRh lattice become shorter when the annealed temperature increase. Annealed at600℃, the film of FePt which is a composite of disordered soft magnetic A1phase and ordered hard magnetic L10phase begins to order and the coercive force magnetized along the vertical direction and the in-plane direction reached respectively6.4kOe and13kOe. Annealed at700℃, the film’s ordering process has been done much more thoroughly. The magnetization curves magnetized along the horizontal direction is almost a straight line through the origin point with a positive slope. When applied magnetic field is along the vertical direction, the coercive force of film is significantly greater than20kOe.2. The coupled bilayer thin film is growed on the heated MgO(001) substrate. According to the different order of growth, thin film can be divided into FeRh/FePt film and FePt/FeRh film. Due to the interlayer diffusion, the upper layer of the film can not suffer from the temperature which is higher than400℃. Because of the high ordered temperature of FePt, the FePt layer of the FeRh/FePt film layer is failed to be ordered. But the ordered FeRh in the FePt/FeRh was successfully done by prolonging the annealing time of FeRh. FePt/FeRh phase transition temperature is significantly higher than FeRh/FePt film, which should be due to the long time of heat treatment to make a few Pt atoms diffuse into the FeRh layer.The hysteresis of magnetization is both observed in FeRh/FePt and FePt/FeRh, which may be due to the supercooling and/or superheating of the parent phase in the product matrix across the magnetic transition. From the magnetization curves at different temperature, the interaction between FePt layer and FeRh layer change from exchange bias to exchange spring as FeRh layer undergoes the magnetic transition. |
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