Effects Of Substrate And Thickness On Structure And Magnetic Properties Of CoPt Film

The 1₀ phase iron group-noble metal binary alloy with face-centered tetragonal(fct)structure has particularly large uniaxial magnetocrystalline anisotropy Ku,small superparamagnetic limit size(several nm),and high coercivity(Room temperature can reach tens of k Oe),squareness ratio(close to 1),and chemical properties are quite stable.There are obvious important applications in the fields of magnetic recording media,magnetic random access memory,micro-nano-sized magnetic sensors,and integrated circuit bias magnets.Among them,the uniaxial magnetocrystalline anisotropy of1₀-CoPt is about 4.9×10⁷erg/cm³,which is not as large as1₀-Fe Pt(7×10⁷erg/cm³).However,it is not as difficult as1₀-Fe Pt to reverse the magnetization direction of nano-scale particles,so it is still favored enough.Generally,CoPt alloy synthesized by magnetron sputtering in a vacuum chamber at room temperature,Co and Pt atoms randomly occupy lattice points to form an A1phase with a face-centered cubic(fcc)structure.High-temperature heat treatment in a vacuum furnace causes the atoms in the solid to overcome the energy barrier and jump,which can transform from a metastable phase to a stable phase.Co and Pt atoms alternately occupy each atomic layer perpendicular to the c axis,that is,1₀ phase.The properties of the magnetic film have a great relationship with the substrate,which is related to the orientation of the film induced by the substrate and the stress generated in the film caused by the substrate.In this paper,three substrates of Si,MgO,Si/MgO(10 nm)are used as substrates,DC sputtering and radio frequency sputtering are used to deposit CoPt films of different thicknesses and structures under different substrates in the vacuum system,and high vacuum is used to quickly heat The high-temperature heat treatment equipment heat-treats the samples at different temperatures.Perform X-Ray Diffraction(XRD)analysis with copper K_?rays(?=0.15406 nm),discuss the crystal structure of the sample,and use a Vibrating Sample Magnetometer(VSM)with a magnetic moment resolution limit of 5×10^-5emu(1emu=10^-3A·m²),maximum magnetic field 15 k Oe)to measure magnetism and hysteresis loop.Use atomic force microscope(Atomic Force Microscope,AFM)to observe the surface morphology,roughness,average height,and maximum height difference of the film.Use magnetic force microscope(Magnetic Force Microscopy,MFM)to observe the changes in the magnetic domain structure of some samples in a magnetic field.The main results obtained are as follows:(1)Si substrate and MgO substrate are selected as substrates,and 50 nm CoPt film is directly grown on the surface.The results show that the key factor for the transformation of CoPt film from disordered fcc(face-centered cubic structure)to ordered fct(face-centered tetragonal structure)is the heat treatment temperature T_a,with the increase of T_a,the coercivity of the CoPt film gradually increases,and the squareness ratio becomes better;Whether it is annelied or not,Si/CoPt(50 nm)(110)peak appears in both,but no vertical orientation is formed,no(001)peak is formed,and the easy axis of magnetization is in-plane;MgO substrates have higher heat resistance than Si substrates and CoPt films.(2)Three samples of Si/MgO(10 nm)/CoPt(x nm)with different film thicknesses(x=30,40,50)were prepared,Whether they were annelied or not,there was no obvious(001),(200),(002)peaks,but(110)peaks appear,indicating that the MgO layer can induce CoPt to produce(110)orientation;compared with the direct growth of CoPt films on Si substrates,the addition of MgO as an isolation layer can isolate CoPt Diffusion with Si substrate to improve heat resistance;After annealing at the same time and temperature,it can be found that the coercivity of Si/MgO(10 nm)/CoPt(30 nm)is greater,in other words,the thinner CoPt film has greater coercivity.(3)Analyzing the magnetic domain structure and magnetization behavior of the Si/MgO(10 nm)/CoPt(x nm)samples with different film thicknesses,it can be found that as the film thickness increases,the gradient of the leakage magnetic field gradually weakens;comparing the AFM images of the unannealed and the annealed samples,it can be found that in the annealed samples,the influence of magnetic force on the atomic force phase will disappear.(4)1₀-CoPt/A1-CoPt double-layer film was prepared on MgO substrate,and non-magnetic MgO was inserted on this basis,and1₀-CoPt/MgO-A1-CoPt three-layer film was prepared.The addition of the MgO intermediate layer can avoid the diffusion of the interlayer,reduce the interface exchange coupling effect,reduce the recording noise,and further regulate the magnetic properties.