| With the man has entered information age, the digital information resources grow in an exponential mode. Today, the storage and security of data facing a challenge which is how to storage most data and keep stable for longtime. Now the main storage media is hard disk drives(HDDs). With increasing areal density in magnetic recording systems, perpendicular recording has successfully replaced longitudinal recording to mitigate the superparamagnetic limit. The extensive theoretical and experimental research associated with perpendicular magnetic recording media has contributed significantly to improving magnetic recording performance. A multilayer composite film based on FePt alloy is presented in this paper. It is well know that the L10 phase FePt and SmCo5 with highest single magnetocrystalline anisotropy Ku. L10 phase FePt has the second largest magnetocrystalline anisotropy of all common magnetic materials. But, unlike SmCo5, it is not only magnetically stable, but also chemically stable. An L10 ordered FePt magnetic particle is thermally stable even its size is as small as 3 nm. Therefore, it was considered as the most promising candidate for future extremely high density magnetic recording media material, especially for the HAMR media. The L10 phase FePt has very large magnetocrystalline anisotropy, and experimentally demonstrated coercivity as high as 105 kOe in FePt thin film. Therefore, the L10 phase FePt particles has so large switching field in such small size, so the issue of improve the areal density and keep thermal stability can be resolve. But the switching field is too large and far exceeds the writing field which write head provided(15 kOe – 18 kOe). The coercivity of magnetic grains of is known to decrease with increasing temperature for common magnetic materials. Therefore, by temporarily heating the media during recording processes, information can be written on the grains with ultrahigh room-temperature coercivity by available write head fields. But there are others problem about heat dissipation and power in HDDs. The switching field decreased in media recording which induced by a material that we needed. FeRh is antiferromagnetic at room temperature and it undergoes a metamagnetic transition to ferromagnetic state at round 100oC. Therefore, this FePt and FeRh multilayer composite films structure can provide thermal stability at room temperatures while the coupling between FePt and FeRh reduces switching field after the metamagnetic transition by slightly heating.In this paper, the single layer of FePt and FeRh, the composite multilayers films structure of the FePt/FeRh and FePt/FeRh/FePt were deposited onto the MgO(001) substrate by magnetron sputtered system. The work is mainly including the follows four aspect:1. The effects of annealing on the structure, magnetic behavior and morphology properties of FePt were analyzed, where the FePt(30nm) were deposited on MgO(001) substrate at400oC.The results showed that the heated MgO(001) substrate can induce the growth of FePt along [001] direction, and the FePt was A1 phase and soft magnetically, and the film continuity, no obvious coercivity. When the 450oC≤Ta ≤ 600oC,the coexistence of two phase in FePt layer and the granular began to appear agglomeration to formed island structure with different size, the coverage rate of films was 100%. Annealing at Ta=700oC, the FePt has ordered, the grains disintegrates as much bigger island-shaped particles, the coverage rate of films was less than 25%.2. Study the structure and magnetic of the FeRh monolayer films. It is found that annealing at 450oC for 24 h, FeRh film has been ordered, and change the annealing temperature the antiferromagnetic-ferromagnetic transition temperature transition did not change significantly.3. The antiferromagnetic-ferromagnetic properties of the FePt/FeRh has been studied and the magnetization curves at different temperature. It was found that during the process of A1 transition to L10 phase, the Pt atom will be precipitated from FePt layer and diffused into FeRh layer. This lead to the first order phase transition temperature of FeRh layer increased to 205oC in FePt/FeRh composite bilayer film. The magnetic stability of the composite film can be improved. The maximum coercivity~7.2kOe. The temperature blows 300oC, the coercivity can be decreased to more than half.4. Try to prepare L10-FePt/B2-FeRh/A1-FePt layer composite film. FeRh forms a thin layer between L10-FePt and A1-FePt and works as an exchange switching layer to turn on/off the coupling between L10-Fe Pt and A1-FePt upon heating/cooling. Preliminary study indicates that the first order phase transition temperature of FeRh in the trilayer composite films was some as FePt/FeRh. Trilayer films compared with the bilayer, the coercivity of the trilayer films was further reduced at different temperature measurement. |
PDF Full Text Request