| Perpendicular magnetic recording is still important,its storage density is aproaching physical limit due to the so-called “trilemma problem” encountered in the development of magnetic recording media.In order to solve this problem,many new materials and technologies based on perpendicular magnetic recording have been put forward by researchers.Exchange coupled composite media(ECC media),as a new type of perpendicular magnetic recording media,has attracted much attention since it can decrease the coercivity while maintaining the thermal stability.In general,ECC media is composed of soft and hard magnetic layers,and can be divided into two kinds of coupling structures,which are:(1)the direct coupling structure with the hard and soft magnetic layers in direct contact and(2)the indirect coupling structure with a middle layer between the soft and hard magnetic layers.A large number of research results show that the soft magnetic layers with negative magnetocrystalline anisotropy can help to reduce the reversal field of the composite particles,that is,the magnetic moment of the hard layer is much easier to turn over under the influence of the soft layer.Therefore,we choose Co Ir with strong negative magnetocrystalline anisotropy and high saturation magnetization as the soft magnetic layer of our ECC media.A series of Co Pt/Co Ir ECC media thin films with excellent properties were prepared by magnetron sputtering.The crystal structure,static magnetic properties and microstructure of the prepared films were studied.The main contents of this thesis are as follows: 1.Preparation of Co Pt hard layer with high perpendicular magnetic anisotropy.In order to induce the c-axis orient growth of the Co Pt hard layer with excellent mangetic properties,we first prepared the seed-layers of Ta,Pt,and Ru with very good properties.In this thesis,the sputtering conditions(sputtering pressure,power and film thickness)of the thin films are explored by means of controlvariables method.By comparing the crystal structure and static magnetic properties of our films obtained under different conditions,we have obtained the optimal sputtering conditions for preparing the Co Pt hard magnetic layer.This is the foundation for further preparation of the ECC media investigated in this thesis.2.Preparation and magnetic properties of Co Pt/Co Ir ECC media thin films.ECC media with a layered structure of Si-substrate/Ta/Pt/Ru/Co Pt/Co Ir were prepared by growing Co Ir soft layer on top of the Co Pt hard layer following the same procedure.Transmission electron microscopy(TEM)results show that the hard-layer of our sample exhibits a columnar type microstructure with well isolated grains and the soft layer with hcp-structure grows on top of the hard layer with the same texture.Therefore,strong coupling of the two layers have been realized as evidenced by the magnetic characterization.Importantly,we observe a more effective reduction of the coercivity of the ECC media by using soft layers with negative magnetocrystalline anisotropy when compared to the use of soft layers with positive or negligible magnetocrystalline anisotropy.The experimental results are corroborated by theoretical calculations.3.Preparation and magnetic properties of Co Pt/Pt/Co Ir ECC media thin films.In order to get Co Pt/Pt/Co Ir ECC media films with better perpendicular magnetic anisotropy,we have prepared three groups of Co Pt/Pt/Co Ir composite films with different Co Ir soft layer thicknesses.Our results show that the introduction of the Pt interlayer can effectively reduce the exchange coupling strength between the soft and hard magnetic layers,thus increasing the rectangular ratio of the media and increasing the perpendicular magnetic anisotropy of the whole film.However,as the thickness of the Pt layer increases,the exchange coupling strength between the soft and hard layers decreases,leading to an increasement of the coercivity of the ECC media. |
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