纳米FePt颗粒:MgO多层复合薄膜的外延生长、微观结构与磁性研究

采用脉冲激光沉积法,在MgO(100)面上外延生长了FePt:MgO多层纳米复合薄膜,FePt成分为Fe48Pt52.FePt纳米颗粒周期性嵌埋于单晶MgO外延层中.原位反射式高能电子衍射分析结果表明,MgO外延层呈层状生长,而FePt纳米颗粒呈岛状生长.在整个FePt:MgO纳米复合薄膜的生长过程中,成功实现了层状-岛状生长模式的交替控制.高分辨透射电子显微镜分析结果表明,退火热处理后,结晶完整的L10-FePt纳米颗粒粒径约为5 nm,呈扁平六角形状,在MgO基底上形成逐层排列的纳米点阵.磁滞回线结果表明,退火后薄膜矫顽力增大,有序度提高,磁性增强.     

Ag对CoPt/Ag纳米复合膜的结构与磁性的影响

采用直流磁控溅射的方法制备了一系列(CoPt/Ag)_n多层膜，然后在不同温度下 进行了退火处理，并对其结构和磁性做了初步的表征，研究了Ag的含量以及薄膜中每一单元 厚度与总厚度对退火后薄膜的结构以及磁性能的影响.结果表明，膜厚较薄时(大约20 nm)有 利于薄膜沿(001)取向生长，Ag的加入不但能够抑制CoPt晶粒的过分长大还可以诱导薄膜的( 001)取向，使退火后的薄膜在垂直于膜面方向上的矫顽力大大增强.对于特定组分为Co ₄₀Pt₄₃Ag₁₇的薄膜，经600℃退火后已经显示了明显的(001) 取向，垂直于膜面方向上的矫顽力为5.6×10⁵ A/m，饱和磁化强度为0.65T, 并 且磁滞回线具有很好的矩形度，剩磁比(s)为0.95. 关键词： 磁记录材料 磁性薄膜 CoPt/Ag纳米复合膜     

氧化物隔离对Si基片上生长L1_0相FePt薄膜磁性的影响

用MgO和SiO_2两种氧化物将FePt薄膜与Si(100)基片隔离,分析隔离层在FePt层发生A1→L1_0转变过程中的作用,寻找用Si母材涂敷L1_0-FePt磁性层来提高磁力显微镜针尖矫顽力的合理方案.采用磁控溅射法在400?C沉积Fe Pt薄膜,在不同温度进行2 h的真空热处理,分析晶体结构和磁性的变化.结果表明:没有隔离层,Si基片表层容易发生扩散,50 nm厚FePt薄膜的矫顽力最大只有5kOe(1 Oe=10~3/(4π)A·m~(-1));而插入隔离层,矫顽力可以超过10 kOe;MgO在Si基片上容易碎裂,热处理温度不能高于600?C,用作隔离层,FePt的最大矫顽力为12.4 kOe;SiO_2与Si基片的晶格匹配更好,热膨胀系数差较小,能承受的最高热处理温度可以超过800?C,使得Fe Pt的矫顽力可以在5 kOe到15 kOe范围内调控,更适合用于制作矫顽力高并可控的磁力显微镜针尖.     

[(Fe/Pt/Fe)/Ag]n多层膜低温合成分离的L10相FePt纳米颗粒

制备了[(Fe/Pt/Fe)/Ag]n多层膜,研究了不同温度退火后的微结构和磁特性.实验结果表明温度高于400℃退火后,样品开始形成L10相的FePt纳米颗粒与Ag基体的复合结构.△M曲线的测量表明FePt颗粒之间不存在交换作用,非常清楚地说明非磁基体Ag有效地隔离了FePt磁性颗粒.有序相的低温合成可能和多层膜结构所造成的界面扩散以及Ag层引入的界面缺陷有关,同时,Ag原子较强的迁移性以及FePt与Ag之间表面自由能的显著差异,使FePt纳米颗粒被Ag隔离.     

利用［Fe/Pt］n多层膜降低L10-FePt有序化温度

采用直流磁控溅射方法制备了Fe/Pt多层膜和FePt单层薄膜，再经不同温度真空热处理得到 了有序相L10₀-FePt薄膜.通过x射线衍射谱和磁性研究表明，FePt单层薄膜需 要在500℃ 以上热处理，才能开始有序化转变，而Fe/Pt多层膜可以降低FePt薄膜有序化温度.［Fe(1 5nm)/Pt(15nm)］13₁₃薄膜在350℃热处理后，有序度已经增加到 06，相应矫 顽力达到了501kA/m.多层膜化促进有序化在较低的温度下进行，这是由于热处理过程中多 关键词： 0-FePt有序相')" href="#">L10₀-FePt有序相 磁控溅射 有序度 Fe/Pt多层膜     

Ag和Ti底层对[Fe/Pt]n多层膜有序化的影响

利用磁控溅射的方法，在热玻璃基片上制备了以Ag，Ti，Cu，Cr，Pt和Ta为底层的［Fe/Pt］_n多层膜，后经不同温度真空热处理，得到L1₀有序结构的FePt 薄膜（L1₀-FePt）.实验结果表明，以Ag和Ti为底层，通过采用基片加温，同时 利用［Fe/Pt］_n多层膜结构，可以促进FePt薄膜的有序化过程，使FePt-L1_０有序化温度从500℃降低到350℃.在较高的温度下退火，以Ag为底层对薄膜的磁性 能影响较小，而以Ti为底层在高于500℃退火后，矫顽力明显下降.在400℃退火20min后，以 Ag和Ti为底层的样品平行膜面的矫顽力分别达到597kA/m和645kA/m，剩磁比分别达到0.81和 0.94，为将来FePt-L1_０有序相合金薄膜用于未来超高密度磁记录介质打下基础. 关键词： ０-FePt薄膜')" href="#">L1_０-FePt薄膜 有序化温度 底层 多层膜结构     

[(Fe/Pt/Fe)/Ag]n多层膜低温合成分离的L10相FePt纳米颗粒

制备了［（Fe/Pt/Fe）/Ag］n多层膜,研究了不同温度退火后的微结构和磁特性.实验结果表明温度高于400℃退火后,样品开始形成L10相的FePt纳米颗粒与Ag基体的复合结构.ΔM曲线的测量表明FePt颗粒之间不存在交换作用,非常清楚地说明非磁基体Ag有效地隔离了FePt磁性颗粒.有序相的低温合成可能和多层膜结构所造成的界面扩散以及Ag层引入的界面缺陷有关,同时,Ag原子较强的迁移性以及FePt与Ag之间表面自由能的显著差异,使FePt纳米颗粒被Ag隔离. 关键词： L10相 FePt 交换作用     

FePt薄膜中磁相互作用

采用磁控溅射方法在自然氧化的单晶Si(100)衬底上制备了纳米结构的Fe₅₃Pt₄₇薄膜，并研究热处理后薄膜中的磁相互作用、晶粒尺寸与热处理温度的关系.经400℃热处理后，FePt薄膜中有明显的面心四方相形成，薄膜表现出硬磁性，晶粒尺度在20 nm，薄膜内部存在软硬磁交换耦合作用；随着热处理温度升高，硬磁相含量增加.同时由于FePt薄膜的晶粒长大，部分软硬磁晶粒之间的交换耦合作用失效；600℃热处理后，FePt的面心立方相已经完全转变为面心四方相，薄膜矫顽力由硬磁相之间的静磁作用贡献. 关键词： 磁性薄膜 纳米晶 磁性能 热处理     

利用[Fe/Pt]n多层膜降低L10-FePt有序化温度

采用直流磁控溅射方法制备了Fe/Pt多层膜和FePt单层薄膜,再经不同温度真空热处理得到了有序相Ll0-FePt薄膜.通过x射线衍射谱和磁性研究表明,FePt单层薄膜需要在500℃以上热处理,才能开始有序化转变,而Fe/Pt多层膜可以降低FePt薄膜有序化温度.[Fe(1.5 nm)/Pt(1.5 nn)]13薄膜在350℃热处理后,有序度已经增加到0.6,相应矫顽力达到了501 kA/m.多层膜化促进有序化在较低的温度下进行,这是由于热处理过程中多层膜界面的消失提供了有序化过程额外的驱动力.     

Co-Pt-C颗粒膜的磁性

利用磁控溅射方法制备多层膜后，再经热处理得到Co-Pt-C颗粒膜.热处理使Co-Pt颗粒从非晶相转向fcc CoPt3和fct CoPt稳定有序相，C则保持非晶态.Pt成分占Co，Pt总体积的70%时，膜的矫顽力Hc可超过400?kA/m.C插层厚度为0.2—0.6nm时，Hc最大，且在磁滞回线上出现“肩膀”.分析认为这是由于存在两个磁性不同的Co-Pt晶相，受C成分比的影响，使它们之间的耦合性质和强度不同造成的. 关键词： Co Pt C 磁滞回线 颗粒膜     

垂直取向FePt/Ag纳米颗粒薄膜的结构和磁性

用磁控溅射法在单晶MgO(100)基片上制备了［FePt 2 nm/Ag dnm］₁₀多层膜， 经真空热处理后，得到具有高矫顽力的垂直取向L1₀-FePt/Ag颗粒膜.x射线衍射结 果表明，在250 ℃的热基片上溅射，当Ag层厚度d=3—11 nm时，FePt颗粒具有很好的［001］取向，随着Ag层厚度的增加，FePt颗粒尺寸减小.［FePt 2 nm/Ag 9 nm］₁₀经过6 00 ℃真空热处理15 min后，颗粒大小仅约8 nm，垂直矫顽力达到692 kA/m.这种无磁耦合作用的颗粒膜，适合用作超高密度的垂直磁记录介质. 关键词： 磁控溅射 垂直磁记录 纳米颗粒膜 0-FePt/Ag')" href="#">L1₀-FePt/Ag     

CoPt–Al 2 O 3 Nanocomposite Films: Synthesis,Structure, and Magnetic Properties

The structure and magnetic properties of CoPt–Al2O3 nanocomposite films synthesized by the annealing of Al/(Co3O4 + Pt) bilayers on a MgO(001) substrate at 650°C in vacuum are investigated. The synthesized composite films contain ferromagnetic CoPt grains with an average size of 25–45 nm enclosed in a nonconducting Al2O3 matrix. The saturation magnetization (Ms ~ 330 G) and coercivity (Hc ≈ 6 kOe) of the films are measured in the film plane and perpendicular to it. The obtained films are characterized by a spatial rotational magnetic anisotropy, which makes it possible to arbitrarily set the easy magnetization axis in the film plane or perpendicular to it using a magnetic field stronger than the coercivity (H > Hc).     

Effect of annealing in an external magnetic field on the microstructure and magnetic properties of the Fe/FePt/Pt multilayer system

The effect of annealing in an external magnetic field applied perpendicular to the plane of the film on the kinetics of Ll ₀ phase transformation of the microstructure and the magnetic properties of the Fe(2 nm)/FePt(20 nm)/Pt(2 nm) multilayer system has been investigated. The relations between the hysteresis loop shape, magnetic correlation length, and structural disorders, which are characteristic of magnetic information carriers, have been analyzed. It has been found that the annealing of the Fe(2 nm)/FePt(20 nm)/Pt(2 nm) multilayer system at a temperature of 470°C in an external magnetic field of 3500 Oe, which is applied perpendicular to the film plane, leads to the formation of a face-centered tetragonal structure of the Ll ₀ phase in the FePt film, which is characterized by the high coercivity H _c , the (001) preferred texture, the magnetic anisotropy perpendicular to the film plane, small sizes of FePt grains in the film, and weak exchange coupling between the particles. The energy of the external magnetic field encourages the process of transformation of the FePt film into the Ll ₀ phase. Thus, a method has been developed for fabricating multilayer films based on the FePt Ll ₀ phase with the parameters necessary for information carrier materials with perpendicular-type magnetic recording.     

Effect of interfacial diffusion on microstructure and properties of FePt/B4C multifunctional multilayer composite films

FePt/B₄C multilayer composite films were prepared by magnetron sputtering and subsequent annealing in vacuum. By changing Fe layer thickness of [Fe/Pt]₆/B₄C films, optimal magnetic property (8.8 kOe and remanence squareness is about 1.0) is got in [Fe(5.25 nm)/Pt(3.75 nm)]₆/B₄C sample whose composition is Fe rich and near stoichiometric ratio. The characterizations of microstructure demonstrate that the diffusion of B and C atoms into FePt layer depends strongly on B₄C interlayer thickness. When B₄C interlayer thickness of [Fe(2.625 nm)/Pt(3.75 nm)/Fe(2.625 nm)/B₄C]₆ films is bigger than 3 nm, stable value of grain size (6-6.5 nm), coercivity (6-7 kOe) and hardness (16-20 GPa) is observed. Finally, the multifunctional single FePt/B₄C composite film may find its way to substitute traditional three-layer structure commonly used in present data storage technology.     

Thickness dependence of microstructure and magnetic properties in FePt/B<Subscript>4</Subscript>C multilayer thin films

FePt/B₄C multilayer films with different single FePt layer thickness were prepared by magnetron sputtering and subsequently annealing in vacuum. Influence of single FePt layer thickness on microstructure and magnetic property of FePt/B₄C films is investigated. Experimental results suggest that the Fe and Pt rich regions will appear in the interior of single FePt layer. The increasing of FePt layer thickness leads to the increase of grain size and volume fraction of order phase f ₀, which eventually induce satisfied coercivity (5.8 kOe).     

Low-temperature ordering and enhanced coercivity of L10-FePt thin films with Al underlayer

FePt multilayer films with and without Al underlayer were prepared by magnetron sputtering on SiO₂ substrate and subsequently annealed in vacuum. Experimental results suggest that the existence of Al underlayer can effectively reduce the ordering temperature and increase the coercivity of FePt films. Due to the slight larger lattice constant of Al underlayer than that of FePt films, [Fe (0.66 nm)/Pt (0.84 nm)]₃₀ films begin to order at 350 °C and the coercivity of them reach to 5.7 kOe after annealing at 400 °C for half an hour.