Effects Of Oxide Isolation Layer On Magnetic Properties Of L1₀ FePt Film Grown

In recent years,with the explosive development of electronic industry,the demand for high-capacity and high-density memory has increased dramatically.In order to achieve ultra-high-density magnetic storage,the smaller grain size is needed.However,the smaller the grain size will lead to higher the superparamagnetic effect and the loss of signal.L1₀-FePt?Face Centered Tetragonal,FCT?hard magnetic alloy has high uniaxial magnetism.Crystalline anisotropy and small superparamagnetic limit size?³ nm?which is an important materials for the fabrication of a new generation of thermally assisted vertical magnetic recording media,exchange-coupled composite magnets and high coercivity magnetic probes.The first part of this paper is to compound L1₀ phase and A1 phase FePt alloy in nano-dimension,and introduce soft magnetic layer to form hard/soft magnetic composite structure.L1₀-FePt/MgO/A1-FePt three-layer films were prepared by inserting non-magnetic MgO isolation layer into the structure.By adjusting the thickness of the isolation layer,improving the coupling between the two phases,one can explore the influence of non-magnetic isolation layer on the magnetic properties of the exchange coupling system.On the other hand,the preparation of MgO substrates is not easy,the price is high,and the process of exchange coupling multi-layer films is complex,which is not conducive to industrial production.In the second part of this paper,a single layer thin film was grown on a cheap Si?100?substrate.The effect of non-magnetic oxide isolation on the magnetic properties and structure of L1₀-FePt was analyzed.It provides a useful reference for the industrialized production of magnetic storage technology and the preparation of high coercivity MFM needle tips with Si as the base material.The analysis is as follows:?1?FePt monolayers with 30 nm thickness deposited on MgO?001?substrates can induce orientation growth of FePt.At T_a=500?,superlattice diffraction peaks FePt?001?and FePt?003?peaks appear and ordering process begins.The film coverage rate keeps 100%,the coercivity is close to 5 kOe,and the magnetization curve is square.T_a=600 C,more A1 phases are transformed into L1₀ phases,Although the coverage rate remains 100%,the coercivity decreases for the more continuous film.T_a=700 C,the film begins to penetrate and the coverage rate decreases.?2?L1₀-FePt?30 nm,500??/A1-FePt?x nm?double-layer magnetic exchange spring was prepared.When the thickness of soft magnet layer?x?is 20 nm,the remnant magnetic ratio in the direction perpendicular to the film surface is close to 1 and keeps a good square,which indicate that whole the soft magnet layers were pinned by the hard magnet layer and magnetized together,showing rigid hard magnetic behavior;when the thickness of soft magnet layer increased to 30 nm,the vertical magnetization curve appeares double shoulder phenomenon.Therefore,the interaction length between layers should be 20 to 30 nm,and the domain wall in the soft magnetosphere should be 180°Bloch type.?3?L1₀-FePt?001??30 nm,500??/MgO?t nm?/A1-FePt?y nm?three-layer film?soft magnet layer thickness?y?is 20 nm?also has double shoulder phenomenon.But the soft magnet layer is strongly affected by the hard magnet layer.When the thickness of MgO?t?is 5 nm,even the soft magnet layer thickness?y?is 30 nm,the domain wall in the soft magnet layer is 180°Bloch type.When t=10 nm and y=30 nm,the soft magnet layer appears 90°domain wall in the soft magnet layer.In-plane magnetization curve without area can produce 180°domain wall in soft magnetosphere,that is,the effect of MgO interlayer to separate soft magnetosphere from hard magnetosphere pinning is more obvious on in-plane magnetization curve.?4?FePt monolayers with 50 nm thickness is deposited on Si?100?single crystal substrates.Without heating treatment,the FePt films deposited at 400?exhibites strong FePt?111?diffraction peaks and weak FePt?200?peaks,which the film is in A1-FePt phase.T_a=600?,the FePt?110?peaks could not be neglected.The area of the loop perpendicular to the film surface also increases and ordering process begins.T_a=700?,there are obvious impurity peaks,and serious diffusion appears between FePt and Si substrates.?5?The magnetic thin films of Si?100?/MgO/FePt and Si?100?/SiO₂/FePt are prepared by adding non-magnetic MgO and SiO₂ as isolation layers.After inserting MgO isolation layer,T_a=500?,FePt?220?peak increase and in-plane coercivity of Hc suddenly increase to 10.7 kOe with A1 phase transformed to L1₀ phase.T_a=600?,in-plane coercivity of A1 phase is 12.4 kOe,which indicates that the phase transition is nearly completed at 500?.T_a=700?,Magnesium oxide layer breaks and the film morphology is destroyed.Superlattice diffraction peaks of FePt?110?and FePt?330?appear when SiO₂ is used as isolation layer when deposited at 400?without heating treatment.After heating treatment at 500?,the in-plane coercivity increases to 10.5kOe.T_a=600?and 700?,the shape of magnetization curve does not change significantly and the coercivity increases to 11.8 kOe and 12.0 kOe respectively.The film ordering process is continuing.The morphology of FePt film remains complete at T_a=800?without serious diffusion.It shows that using SiO₂ as isolation layer can not only reduce the ordering temperature of FePt but also make the film not easy to damage or deteriorate.?6?Si?100?/SiO₂/FePt?x nm,T_a=600??was prepared by using SiO₂ as isolation layer.Comparing the thickness effect of film magnetism,it can be concluded that using L1₀-FePt as magnetic coating for MFM tip should not be less than 20 nm to maintain the continuity of FePt layer with SiO₂ Isolation layer.