Structure And Magnetic Properties Of L1₀-FePt Based Coupling Thin Films

Magnetic recording media play an important role in current data storage.The demand for better information storage devices is growing rapidly.It is an urgent need to study magnetic recording media with high recording density and reliable operating performance.FePt alloys have attracted much attention in recent years because of their excellent magnetic properties and high chemical stability.Therefore,they have potential applications in the basic research of advanced systems and devices.But the flipping field is much larger than the magnetic head writing in the field,which makes it difficult to write the information.Then the exchange spring and the exchange coupled magnetic recording medium are put forward,the soft magnetic drive hard magnetic reversal,the hard layer and the soft layer coupling to reduce the switching field,while maintaining the thermal stability.In this paper,the film was deposited on MgO?001?substrate at 400?by magne-tron sputtering.The vacuum heat treatment was performed at 2 h,T_a=[500?,700?],and its morphology,structure and magnetic properties were studied.The surface of the film after heat treatment at 500?and 600?is smooth and continuous,which shows hard magnetism and the coercive force is not very large.It will continue to grow A1-FePt or MgO/A1-FePt on it to reduce the requirement of the medium,and analyze its magnetic characteristics.The following conclusions are obtained:?1?the monolayer FePt film of 30 nm thick is grown on the MgO?001?substrate.The surface of the film without heat treatment is smooth and smooth and the grain size is small.It grows along?001?direction with a disordered soft magnetic phase.The magnetization is easy to be in the surface and the coercivity is small.After heat treatment,different degrees of phase transition occurred.T_a=500?,the magnetic domain is clear,the film phase changes,the L1₀ phase has been formed,the order degree is 0.6,the magnetization is changed from the surface to the vertical film surface,and the coercive force is obviously increased.T_a=600?,the grains fuse into large single crystals,the magnetic domain increases,the domain walls move freely in the single crystal,and the coercive force decreases.T_a=700?,the films are basically ordered,but both continuous and epitaxial growth are destroyed.?2?L1₀-FePt/A1-FePt double layer exchange spring membrane,AFM image and monolayer,there is no obvious difference,but the magnetization curve of the double shoulder phenomenon,magnetization reversal is completed in two steps.In the H>H₁segment,the A1-FePt closest to the upper surface is separated from the exchange effect of the hard magnetic phase,the magnetization intensity is not saturated,and the magnetic moment tends to be directed toward the in-plane direction.In the H₂<H<H₁section,the A1-FePt near the hard magnetic/soft magnetic interface is pinned by the hard magnetic phase,the slope of the magnetic intensity decreases,and the magnetic moment directing to the vertical direction.When H=H₂,the domain wall in the A1-FePt layer breaks through the hard magnetic/soft magnetic interface into the L1₀-FePt layer.Therefore,the H<H₂ section is the process of magnetization reversal in the hard magnetic layer,and the slope of the magnetization decrease is greater.T_a=500?,the area of the bright and dark area in the MFM diagram becomes larger.The soft magnetosphere covered by the covering makes the particles separated from the hard magnetosphere coupled with the soft magnetosphere,forming an exchange spring and reducing the coercivity.T_a=600?,the area of bright and dark area in MFM diagram increases,and the hard magnets of large crystals are shielded by soft magnetic force,and some magnetic lines of force are closed,so the coercivity increases slightly.?3?L1₀-FePt/MgO/A1-FePt three layer exchange coupling film,when the growth temperature of the MgO layer is room temperature,compared with the double layer film,after inserting the middle layer MgO,the shoulders are more obvious.Because the interlayer separates the direct exchange between the soft and hard magnetic field,the domain wall can not enter the hard magnetic layer directly after the reverse magnetic domain nucleation is large during the reverse magnetization process 500?.The coerci-vity of the film after heat treatment is larger,but the change of the thickness of the middle layer has little influence on the coercive force.When the growth temperature of MgO is 400?,the magnetization curve is more stable and the magnetization curve in the surface is more abrupt in the vicinity of the zero magnetic field.The length of the exchange action is 35 nm<l_ex<40 nm,indicating that the growth temperature of MgO in the middle layer is higher.The crystallinity is better,but the worse the hard magnetic layer is,the more unclear the grain boundary is.The films with heat treatment at 600?have good crystallinity and continuity.The coercivity of the magnetization curve is the same as that of the bilayer.