【作者】 李宝河；

【导师】 朱逢吾；

【作者基本信息】 北京科技大学 ， 材料物理与化学， 2005， 博士

【摘要】 在超高密度磁记录中,记录介质的稳定性成为关键问题。要进一步提高磁记录密度,磁性记录晶粒的尺寸将低于10nm,这样小的晶粒尺寸,热扰动引起的超顺磁行为将影响磁记录介质的稳定性。L10-FePt有序合金由于具有极高的磁晶各向异性（7×10⁶J/m³）,可以在极小晶粒尺寸（3⁵nm）下仍能具有很好的热稳定性。所以近年来对L10有序结构的L10-FePt薄膜的研究成为磁记录的一个热点。L10-FePt相纳米复合薄膜作为超高密度垂直磁记录介质的实用化还需解决两个关键问题:一是降低L10-FePt薄膜的有序化温度;二是L10-FePt颗粒薄膜的垂直（001）取向。本文针对这两个问题进行了系统的研究。（1）　FePt薄膜的低温有序化研究利用磁控溅射法制备了系列FePt和FePtCu单层膜,薄膜厚度控制在50nm。利用直流共溅射方法精确控制Fe和Pt的原子比。实验结果表明, Fe和Pt的原子比为1.1:1的Fe₅₂Pt₄₈样品在350℃真空热处理20 min后,矫顽力达到605 kA / m,有序度达到0.87,实现了较低温度下FePt薄膜的有序化。Fe₅₂Pt₄₈样品中添加Cu不能促进FePt的有序化,但是对于FePt化学原子定比或富Pt的样品,添加Cu可以促进FePt有序化,当（FeCu）/Pt原子比达到1.1¹.2的范围时,即可实现较低温度的有序化。对于Fe₅₂Pt₄₈薄膜,研究了薄膜厚度、退火温度、退火时间对薄膜有序化的影响。结果表明,在较低的温度下退火,样品的厚度和退火时间均起着很重要的作用。在热处理温度低于400℃时,样品的有序度和矫顽力随样品厚度的增加而提高,但当薄膜厚度大于50nm后,厚度的变化对薄膜有序度的影响不大。当FePt的成分为Fe49Pt51时,利用Fe/Pt多层膜和FePt/Cu多层膜化可以降低FePt薄膜有序化温度。与Fe49Pt51（40nm）单层薄膜相比,利用多层膜化可以使有序化温度降低约100℃。以Ag和Ti为衬底层,在400℃热处理后,发现能够有效提高[Fe/Pt]n多层膜的矫顽力。经400℃退火20min后,以Ag为底层的样品平行膜面的矫顽力达到597 kA/m,以Ti为底层的样品400℃退火20min后,矫顽力可达到645kA/m。（2）　FePt纳米颗粒薄膜的垂直取向研究在MgO单晶基片上利用磁控直流共溅射的方法制备了不同厚度的FePt薄膜,并经600℃真空热处理15min。溅射过程中基片保持室温或250℃恒温。结果表明:加热基片有助于获得较好的L10-FePt（001）织构。薄膜厚度越小,越有利于FePt薄膜沿MgO（001）单晶异质外延生长,从而可获得较好的沿膜面法向取向[001]生长。对于溅射时基片保持250℃恒温,厚度仅为5nm的FePt薄膜,垂直矫顽力达到240 kA/m,晶粒平均尺寸为7 nm,具有很好的垂直磁各向异性。在热MgO基片（250℃）制备了FePt/BN颗粒薄膜。[FePt （2nm）/ BN （0.5nm）]10多层膜和[FePt （1nm）/ BN （0.25nm）]20多层膜经700℃真空热处理1h后,获得具有良好垂直取向的L10-FePt/BN颗粒膜。样品具有很强的垂直磁各向异性,且垂直磁滞回线的矩形度很好,具有很好的开关特性。用磁控溅射在单晶MgO（100）基片上制备了[FePt （2nm）/Ag （d nm）]10多层膜,通过加热基片和精确控制FePt薄膜中的Fe和Pt原子比,提高了薄膜矫顽力而且实现了FePt/Ag颗粒薄膜垂直取向,得到具有高矫顽力垂直取向的L10-FePt/Ag颗粒膜。随着Ag层厚度的增加,L10-FePt晶粒尺寸减小。一个典型的结果是[FePt （2nm） /Ag （5nm）]10多层膜经600℃真空热处理15min后,多层膜界面消失形成颗粒膜,L10-FePt晶粒大小仅约8nm,具有很好的垂直磁各向异性,垂直矫顽力达到979 kA / m。δM的研究结果表明,晶粒间无磁交换耦合作用。这种无磁耦合作用的颗粒膜,适合用于将来超高密度的垂直磁记录介质。以上对降低FePt薄膜有序化温度和控制FePt[001]垂直薄膜取向的研究,对未来超高密度垂直磁记录介质的实用化有重要参考意义。更多还原

【Abstract】 To further improve the density of magnetic recording meadia, the magnetic grain size should be reduced to below 10 nm. But at this level of grain size, the superparamagnetic effect caused by thermal fluctuation will affect the thermal stability of magnetic recording media. With large magnetocrystalline anisotropy （ Ku = 7×106 J/m3）, the L10-FePt ordering alloy film has good thermal stability even when the grain size is about 5nm. So the L10-FePt ordering film has recently become a hot issue in magnetic recording field. However, for ultrahigh density perpendicular magnetic recording media, two key issues for the application of L10-FePt nanoparticle films remain to be solved: one is to decrease the ordering temperature of L10-FePt nanoparticle films, the other to obtain the L10-FePt nanoparticle films with perpendicular （001） texture. This dissculation has pyetematically inrestigated the two issues.（1） Study on the reduction of the ordering temperature of FePt thin films Series of FePt and FePtCu thin films with a fixed thickness of 50nm have been prepared by magnetron sputtering. The atomic ratio of Fe to Pt atoms have been accurately controlled by DC co-sputtering. After vacuum annealing at 350℃for 20 min, the coercive force of about 605 kA/m is obtained for the Fe₅₂Pt₄₈ thin films （The atomic ratio of Fe to Pt atom is 1.1:1） with the ordering parameter of about 0.87, which leads to the ordering of the FePt thin films at a lower annealing temperature. The ordering of the FePt thin films is not enhanced by the addition of Cu to Fe₅₂Pt₄₈ films, but the addition of Cu to the Pt-rich or stoichiometric thin films couled promote the L10 FePt ordering. As a rule, we find that L10 phase can be obtained at a lower annealing temperature only for the films with the ratio of the （FeCu） : Pt in the range of 1.1¹.2.The effects of films thickness, annealing temperature and time on the ordering of Fe₅₂Pt₄₈ films have been studied. When the films are annealed at a temperature lower than 400℃, theordering parameter and the coercive force increase with the increase of the thickness of the films. The thickness has little effect on the ordering parameter when the film is thicker than 50 nm.With a fixed composition of Fe49Pt51 films, the ordering temperature of FePt thin films can be lowered by the preparation of Fe/Pt multilayers or FePt/Cu multilayers. Compared with Fe49Pt51 films （40nm）, the ordering temperature of Fe/Pt multilayers can be decreased by about 100℃. The coercive force of [Fe/Pt]n multilayers is significantly increased by sputtering Ag or Ti underlayer on the glass substrate. After vacuum annealing for 20 min at 350°C, the coercive force of about 597 kA/m and 645 kA/m is obtained for multilayers with Ag and Ti underlayer, respectively. Meanwhile, the surface roughness and the surface particle size of multilayers with Ti underlayer are close to those of the films without any underlayer.（2） Study on the perpendicular orientation of FePt nanoprticle filmsThe FePt thin films with different thickness have been prepared on （100） MgO single crystal substrates with magnetron sputtering and then vacuum annealed at 600℃for 15 min. The substrate temperature is kept at ambient temperature or 250℃. It has been found that heating of the substrate is useful for the formation of strong L10-FePt （001） texture. The thicker the thin film is, the better its epitaxial growth on MgO （100） single crystal, which leads to oriental growth along the [001] direction normal to the film plane. For the 5nm FePt thin film prepared on the 250℃substrate, the coercive force can reach 240 kA/m and the average grain size is 7nm, showing good perpendicular magnetocrystalline anisotropy.FePt/BN particle films have been prepared on the heated MgO substrates （ 250℃） . L10-FePt/BN particle films with strong perpendicular orientation can be obtained after [FePt（1nm）/BN（0.25nm）]20 multilayer has been vacuum annealed at 700℃for an hour. The results have shown strong perpendicular magnetic anisotropy and good squareness.[FePt （2nm）/Ag （d nm）]10 multilayers have been prepared on MgO （100） single crystal substrates with magnetron sputtering. The low ordering temperature and perpendicular orientation of L10-FePt/Ag particle films with high coercivity have been obtained by controllingaccurately the atomic ratio of Fe to Pt of L10-FePt films and heating the substrate. The average size of L10-FePt grains decreases with the increasing the thickness of Ag layer.A typical example is the [FePt （2nm）/Ag （5nm）]10 multilayers after vacuum annealed at 600℃for 15 min. The interface in multilayers disappears and a particle film is obtained. The average size of L10-FePt grains is about 8nm, and its perpendicular coercive force reaches 979 kA/m.δM results has shown that this particle film has little magnetic exchange coupling.The above results about the ordering of FePt thin films at a lower temperature and control of FePt [001] perpendicular orientation are very useful for the application of future perpendicular magnetic recording media with ultrahigh density.更多还原