Preparation Of Fept Hard Magnetic Composite Magnetic Recording Film On Si(001) Substrate

With the rapidly rising of the data amount,demands for more efficient digital information storage techniques continue to increase.Therefore,it is of great importance to develop disks with higher magnetic storage density.Using the CoCrPt system as a recording medium,an areal storage density of 100 Gbit/in² has been obtained at present through perpendicular magnetic recording technology.To raise the storage density beyond 100 Gbit/in²,the grain size of the recording material should be reduced to nanoscale.Below the critical dimension,the superparamagnetic limit is more pronounced,and the magnetization of the particles becomes unstable due to thermal fluctuations.Thus,this system is unsuitable for permanent magnetic storage.However,in order to increase this value to a new limitation of 1 Tbit/in² to satisfy the growing requirements,we must find new materials and improve corresponding process technology.L1₀-FePt is one of the most promising candidate materials for ultra-high density magnetic storage,due to its excellent properties,i.e.high uniaxial magnetocrystalline anisotropy?K_u=7.0×10⁷ erg/cm³?,high coercivity,high saturation magnetization and good chemical stability.In addition,the high anisotropy of the FePt system increases the anisotropic energy?K_uV?.And when the L1₀-FePt particle size is as low as 3 nm,it shows good thermal stability.Hence,using FePt as a kind of magnetic storage medium could substantially increase the areal density.And it is the first choice for ultra-high density magnetic recording materials.Most researchers employ epitaxial FePt?001?thin films synthesized on single crystal MgO substrates to produce FePt films.However,MgO is easy to be affected with damp and the cost of single crystal MgO substrate is very high,which make MgO unattractive.This article focuses on studying a different substrate of single crystal Si?001?.Since silicon is cheap and readily available,and more importantly,we can also integrate the storage component with various microelectronic devices through Si?001?substrates.In this paper,Si?001?is used as the base material,and a FePt monolayer film and a FePt multilayer film with a buffer layer of MgO are deposited by magnetron sputtering method.The effect of the buffer layer on the structure and magnetic properties of the prepared FePt thin film was analyzed.The results of this paper are as follows:1.FePt?50nm?and MgO?10nm?/FePt?50nm?thin films were prepared with an MgO buffer layer in them.The MgO buffer wasn't added at first.Then Fe and Pt atoms diffused into the Si lattice and the FePt preferred to grow along?111?plane.It is not desirable to grow FePt directly on Si substrate.Therefore,it is necessary to add an MgO buffer layer to control the growth orientation of FePt.Insertion of the MgO layer as a stencil buffer medium results in the growth of FePt along a hard magnetic[001]orientation.2.The MgO buffer layer controls the growth of FePt along the hard magnetic c-axis,and it also acts as an effective diffusion barrier.When the heat treatment temperature reaches 600°C,the coercive force is large,and it is found that the non-magnetic MgO could be used to adjust the coercive force of the film.MgO?10nm?/?FePt+MgO??51 nm?films and MgO?10 nm?/??MgO+FePt??10.2 nm?co-sputtering-MgO?2 nm??films were fabricated next.The co-sputtering effect of the magnetic substance causes the non-magnetic MgO layer to intercalate between the two phases,and affect the exchange coupling interaction between the two phases to adjust the coercive force.And the influence of the latter film is more pronounced.3.Exchange-coupled thin films with an isolation layer?10 nm?made of MgO were also prepared,including L10-FePt/FePt?a nm?,?FePt+MgO?co-sputter/FePt?b nm?,L1₀-FePt/Fe?c nm?/MgO?10 nm?and?FePt+MgO?co-sputtering/FePt?d nm?/MgO?10 nm?.Among them,a=b=20-30 nm,the phenomenon of in-plane hysteresis loop shoulders is obvious,indicating that the thickness of soft magnetic layer is higher than the critical thickness.For films when b=20-30 nm,the coercive force is larger because doped non-magnetic material MgO weakens the coupling effect between magnetic particles.The length of hard and soft magnetic exchange coupling of L10-FePt/FePt system is 20-30 nm.When c=d=10 nm,the in-plane hysteresis loop presents a distinct double shoulder status because the thickness of the soft magnetic layer has exceeded the exchange coupling length.Therefore,the L1₀-FePt/Fe hard magnetic exchange coupling length is 6-10 nm,while the?FePt+MgO?/Fe hard magnetic exchange coupling length is 4-6 nm,which is due to that the incorporation of MgO particles between the magnetic particles make the coupling effect weak.