Exchange Coupling Properties Of In-plane Oriented L1₀/A1-FePt Bilayer Films

The capacity of information record has shown growth of power series since the rapid development of IT industry and continuous improvement of information technology.Therefore,it is urgent to develop the ultra-high density magnetic recording media.With the swift evolution of signal processing technology,properties of medium turn into the key limitation of storage density.Some researchers have proposed diverse approaches,in order to solve the corresponding problems,e.g.the restriction of head write field and the thermal disturbance caused by the loss of information.Exchange coupling effect could effectively reduce the coercivity of hard magnetic particles so as to achieve the needs of writing.And the high magnetocrystalline anisotropic hard magnetic particles could shrink the magnetic recording unit to further improve the magnetic storage density.In addition,thermal auxiliary magnetic recording could also overcome the material problems.However,these methods are often restrictive.Thus,the direct transformation of the structure of material itself has become indispensable in this field.Among the plenty of substances,FePt is a kind of ideal material to manufacture the magnetic recording exchange coupling medium due to its stable hard magnetic and soft magnetic phases at room temperature.Moreover,the utilization of FePt,which is different heterogeneity of the same material,could overcome the problem that the lattices do not match.In this paper,the two-layer structure of the exchange coupling was studied based on the excellent properties of FePt.And the corresponding characteristics were studied detailed the magnetization reversal mechanism.Both the vertical exchange coupling and the in-plane exchange coupling could improve the magnetic recording density.Besides,the exchange of coupling media on different substrates will result in materials with different easy axis,Hence the choice of substrate is also important.FePt was sputtered on different substrates to prepare FePt films.Then the films were annealed at diverse temperatures for 2 h to obtain L10-FePt.The vertical magnetic recording exchange coupling medium requires that the magnetization easy axis perpendicular to the film surface direction,while the in-plane magnetic recording exchange coupling medium requires the magnetization of the easy axis in the in-plane direction.Therefore,the vertical magnetic recording of exchange coupling medium was prepared by using Si(001)substrate and MgO(001)substrate,and the in-plane magnetic recording exchange coupling medium was prepared by MgO(110).Since the difference between the lattice constants of monocrystalline Silicon and FePt,lots of lattice distortion will emerge in the growth process.According to the experimental data,FePt diffused intensely in the films through the high temperature heat treatment,and magnetization easy axis that was perpendicular to the membrane didn't appear in the films in which no strongly diffusion occurred.The lattice constant of MgO is between that of Si and FePt.Thus MgO was employed as the isolation layer to get(001)texture.And then FePt got its epitaxial growth to achieve(001)texture.Nevertheless,the experimental results showed that the magnetization easy axis wasn't perpendicular to the membrane and the MgO layer only separated the substrate and the FePt film.Although FePt could present(001)texture with the direct use of MgO(001)substrate.And also the magnetization was vertical to the film surface.Considering it is necessary to see the exchange coupling properties and measure the in-plane exchange of coupled samples to study the intrinsic properties of exchange coupling.Therefore,the MgO(001)substrate was not taken into account.The in-plane orientation,which was necessary to get the in-plane exchange coupling,existed in FePt film grown by the MgO(110)substrate.After the heat treatment at 500 ° C,it was possible to obtain L10-FePt with a magnetically easy axis in the plane and a hard magnetic property required.The soft magnetic layers with different thicknesses were grown on hard magnetic layers with different thicknesses to explore the relationship between the thickness and exchange length of the exchange coupling.After the heat treatment at 500 ?,the exchange length of FePt film of 30 nm was between 20-30 nm.In the exchange coupling medium,an MgO layer of 10 nm was insert to separate the soft magnetic layer from the hard magnetic layer.And it was found that the soft magnetic layer exceeding the length of the exchange coupling was also restricted by the exchange coupled composite.The existence of the MgO layer made it easier for the soft magnetic layer over the exchange coupling length to reverse the magnetization.