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题名 超过密度磁记录磁头材料Fe-Co薄膜的研究
姓名 付煜
院系 物理科学与技术学院
专业 凝聚态物理
学位名称 理学博士
外文题名 Studies of FeCo Thin Films for Ultra-high Density Magnetic Recording Write-head
第一导师姓名 杨正
关键词 磁记录材料;溅射薄膜;FeCo;软磁性
外文关键词 magnetic recording materials;sputtering thin films;FeCo;soft magnetic properties
学科 理学
摘要 对于超高密度的纵向磁记录和垂直磁记录,使用高饱和磁化强度的材料作为写头磁极材料是其本质要求。对于成分为Fe65Co35的Fe-Co合金是一种很有竞争优势的材料,因为在铁磁材料中,它具有最高的饱和磁化强度24.5 kG. 但是Fe-Co合金薄膜由于本身具有大的磁晶各向异性和饱和磁致伸缩,因此一般具有大的矫顽力。本论文主要研究了选择合适的衬底材料来降低Fe-Co薄膜的矫顽力,从而获得良好的软磁性能。得到了以下结果: 1. 通过两种方法成功制备了软磁性的高饱和磁化强度的FeCo薄膜:平面磁控溅射和对向靶溅射。 2. 采取平面磁控溅射系统,研究了Ni79Fe21, Co100-yFey(0≤y≤11), Cu和Fe衬底对Fe65Co35薄膜微结构和软磁性的影响。对于FeCo单层Co含量在30~40 at.%的成分区域内,薄膜具有高的饱和磁化强度4Ms~24 kG,基片温度为360 oC时,Fe65Co35(100 nm)薄膜的矫顽力为20 Oe。采用Ni79Fe21(1-10 nm), Co93Fe7 (1-10 nm), Cu(1-3 nm)的衬底,Fe65Co35 (100 nm)薄膜获得了优秀的软磁性和面内单轴各向异性,4Ms~24 kG,Hce ~11-14 Oe, Hch~ 1-3 Oe, Hk ~ 50~80 Oe。薄膜的软磁性与微结构有密切的关系。XRD结果表明,Fe65Co35单层薄膜具有(110)择优取向,而在衬底层Ni79Fe21 (1-10 nm), Co93Fe7 (1-10 nm), Cu(1-3 nm)上生长的 Fe65Co35薄膜的择优取向为(200); 对于Cu衬底具有厚度依赖性,当Cu衬底厚度大于3nm,Fe65Co35薄膜的择优取向又变成(110), 同时矫顽力增加;Fe(1~5 nm)衬底没有改变Fe65Co35薄膜的择优取向,对薄膜的软磁性改善方面也不是很好。 3. 采用对向靶溅射系统,研究了Co衬底对Fe65Co35薄膜的应力,织构,晶粒尺寸,形貌,以及起始生长的影响。Fe65Co35薄膜具有几乎各向同性的面内磁滞回线和大的矫顽力>100 Oe。Fe65Co35(200 nm)/Co(5 nm)薄膜展现出良好的面内单轴各向异性:4Ms~24 kG,Hce ~10 Oe, Hch~ 3 Oe, Hk ~ 60 Oe。Fe65Co35(400 nm)/Co(5 nm)薄膜的有效磁导率为250,铁磁共振频率为1GHz。对于Fe65Co35单层薄膜饱和磁致伸缩为5.2  10-5,内应力为0.8 GPa,采用衬底层后二者均有所降低。Fe65Co35单层薄膜的织构具有厚度依赖性,当膜厚小于200 nm时,薄膜为(200)织构,随着膜厚的增加,转变为(110)织构。采取Co衬底层抑制了Fe65Co35薄膜的(200)织构,在不同的厚度范围,均表现出(110)织构。Co衬底的采用使Fe65Co35薄膜的晶粒尺寸D大大降低:Fe65Co35单层D~74 nm,Fe65Co35/Co (5 nm)薄膜D~8.2 nm。 4. FeCo/Co薄膜矫顽力的大大降低可以通过晶粒尺寸效应来解释,这与Hoffmann的涟波理论是一致的。 5. 薄膜软磁性的改善伴随着织构的演变,并且对两种溅射系统,表现出相反的织构改变。衬底对薄膜织构的影响可以用薄膜的生长模式和表面自由能最小解释。 6. 软磁材料的高频应用,磁各向异性为一个很重要的参数。对于磁各向异性场Hk的控制主要采用了两种方法。一种是通过调整基板-靶的距离改变薄膜的微结构来控制薄膜的各向异性,另一种是采用预弯曲的基片感生应力各向异性,获得的最大的Hk为250 Oe, 并且保持了良好的软磁性。
外文摘要 The use of high-moment pole materials in inductive write heads is an essential requirement to achieve adequate writeability at ultrahigh areal density longitudinal as well as perpendicular magnetic recording. Fe-Co alloy with composition around Fe65Co35 is a competitive candidate because of the highest saturation magnetization 4Ms of 24.5 kG among ferromagnetic materials. But it has large magnetocrystalline anisotropy (10 kJ/m3) and large magnetostriction (4-6×10-5), which results in potentially high covercivity Hc. In this thesis, The method that uses suitable underlayers to give rise to soft magnetic properties in Fe65Co35 thin films was studied. The results are as follows: 1. Magnetically soft FeCo thin films were prepared successfully using two deposition methods: (1) conventional planar magnetron sputtering. (2) facing targets sputtering. 2. By planar magnetron sputtering system, excellent soft magnetic properties were obtained by choosing suitable underlayers: Ni79Fe21, Cu and Co93Fe7. For FeCo singelayer, the saturation magnetization is as large as 24 kG in the composition range of Fe100-xCox (30x40). Films have coercivity as large as 150 Oe sputtered at room temperature. With the sputtering temperature increasing, the value of coercivity decreases rapidly to 24 Oe at 360 C. The soft magnetic properties of Fe65Co35 films are much improved by using the underlayers: 4Ms~24 kG,Hce ~11-14 Oe, Hch~ 1-3 Oe, Hk ~ 50~80 Oe. It is found that the texture of Fe65Co35 with an underlayer is dependent on the material and the thickness of underlayer. It indicates that soft magnetic properties are much improved with the texture change from (110) type to (200) type. 3. By facing targets sputtering system, the effect of Co underlayer on stress, texture, grain size, morphology, initial growth and interface was studied systematically. The FeCo single layer shows almost isotropy with the coercivity larger than 100 Oe. FeCo/Co films exhibit a well-defined in-plane uniaxial anisotropy with coercivities of 10 Oe and 3 Oe along the easy axis and the hard axis. The effective permeability of the films remains flat around 250 up to 800 MHz. The saturation magnetostriction is 5.2  10-5 and the intrinsic stress is 0.8 GPa in FeCo single layer, both are slightly reduced by Co underlayer. The Co underlayer changes the preferred orientation of the FeCo films from (200) to (110), but more significantly, reduces the average ...
研究领域 磁学与磁性材料
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