（001）-oriented FePt/Ag composite films for perpendicular recording

FePt/Ag thin films were deposited by magnetron sputtering onto 7059 glass substrates, then were annealed at 550 ℃ for 30 min. Nanostructured FePt/Ag films were successfully obtained with the magnetic easy axis of L10 FePt perpendicular to the film plane. It was found that the development of (001) texture depended strongly on the thicknesses of FePt magnetic layer and Ag underlayer. The L10 ordered FePt(15 nm)/Ag(50 nm) with (001) orientation can be obtained. And the perpen-dicular coercivity of FePt(15 nm)/...     

Magnetron sputtering deposition of [FePt/Ag]n multilayers for perpendicular recording

[FePt/Ag]n multilayers were deposited on glass substrates by RF magnetron sputtering and ex situ annealed at 550℃ for 30 min. The effects of inserted Ag layer thickness and the number of bilayer repetitions （n） on the structure and magnetic properties of the multilayers were investigated. It was found that the difference between in-plane and out-of-plane coercivities varied with an increase of inserted Ag layer thickness in the [FePt 2 nm/Ag x nm]10 multilayers. The ratio of out-of-plane coercivity to in-plane coercivity reached the maximum value with the Ag layer thickness of 5 nm, indicating that the Ag layer thickness plays an important role in obtaining perpendicular orientation. For the [FePt 2 nm/Ag 5 um]n multilayers, perpendicular orientation is also influenced by n. The maximum value of the ratio of out-of-plane coercivity to in-plane coercivity appeared when n was given as 8. It was found that the [FePt 2 nm/Ag 5 nm]8 had a high perpendicular coercivity of 520 kA/m and a low in-plane one of 88 kA/m, which shows a strong perpendicular anisotropy.     

Effect of Ni doping on the microstructure and magnetic properties of FePt films

FePtNi films with different Ni contents were deposited on glass substrates by RF magnetron sputtering, and the Llx-FePtNi films were obtained after the as-deposited samples were subjected to vacuum annealing. The magnetic properties, structures, and orientations of the Llx-FePt films with Ni doping were studied. The results show that with increasing Ni content, the (001) peak position of the FePtNi films shifts to a higher angle in comparison with FePt. which suggests that there is partial Ni substitution in the Ll0 lattice. The perpendicular coercivity decreases from 661 to 142 kA/m and magnetization decreases from 512 to 433 kA/m with increasing Ni content. In comparison with FePt films, the FePtNi films can effectively reduce the Curie temperature, which makes FePtNi fdms promising media candidates in thermally assisted recording (TAR).     

Micromagnetic studies of perpendicular recording FePt media with controllable grain size distributions

A 3-dimensional (3D) micromagnetic model combined with Fast Fourier Transform (FFT) method was built up to study the writability in the L10 FePt perpendicular medium. The effects of controllable grain size distributions were studied by grain growth simulation. It is found that the cross-track-averaged magnetization changes little between the L10 FePt medium with uniform or non-uniform grain size distribution.     

Effects of Ag layers on the SiO2/FePt thin films deposited by magnetron sputtering

The effects of Ag layers with different locations and thicknesses on the structural and magnetic property of SiO2/FePt multilayer films were investigated.The non-magnetic Ag layer plays an important role in inducing（001） orientation and ordering of FePt grains,as well as the SiO2-doping reducing the grain size and the magnetic exchange coupling between grains.When the 10 nm Ag layer is moved from the bottom to the top of the SiO2/FePt multilayer film,the coercivity gradually decreases;the largest difference between the out-of-plane coercivity and the in-plane one is obtained in the sample of [SiO2（2 nm）/FePt（3 nm）]3/Ag（10 nm）/[SiO2（2 nm）/FePt（3 nm）]2.Furthermore,the location of Ag layers was fixed and the thickness was changed.The XRD curves suggest that the intensity of the（001） peak becomes the strongest with the addition of 10 nm Ag layers.     

Ti衬底层对FePt颗粒膜的微结构和磁特性的影响

在室温下,应用对靶直流磁控溅射设备在普通玻璃基片上制备了FePt(30nm)/Ti(tnm)颗粒膜样品,随后,在真空中进行了原位退火.详细研究了Ti衬底层对FePt颗粒膜的微结构和磁特性的影响.X射线衍射图谱表明样品形成了较有序的L10织构,Ti和FePt形成了三元FePtTi合金.当Ti层厚度t=5 nm、退火温度Ta=500℃时,样品具有高度有序的L10织构、小的颗粒尺寸和优异的磁特性.矫顽力超过了6.7 kOe,饱和磁化强度为620emu/cc.并且具有较小的开关场分布.结果表明FePt/Ti颗粒膜系统可作为超高密度磁记录介质的候选者.     

Ti衬底层对FePt颗粒膜的微结构和磁特性的影响

在室温下,应用对靶直流磁控溅射设备在普通玻璃基片上制备了FePt(30nm)/Ti(tnm)颗粒膜样品,随后,在真空中进行了原位退火.详细研究了Ti衬底层对FePt颗粒膜的微结构和磁特性的影响.X射线衍射图谱表明样品形成了较有序的L10织构,Ti和FePt形成了三元FePtTi合金.当Ti层厚度t=5 nm、退火温度Ta=500℃时,样品具有高度有序的L10织构、小的颗粒尺寸和优异的磁特性.矫顽力超过了6.7 kOe,饱和磁化强度为620emu/cc.并且具有较小的开关场分布.结果表明FePt/Ti颗粒膜系统可作为超高密度磁记录介质的候选者.     

Effects of Ag layers on the microstructure and magnetic properties of CoPt/BN multilayer films

Ag/[BN/CoPt]5/Ag and [BN/Ag/CoPt]5/Ag thin films were deposited on glass substrates by magnetron sputtering and then annealed in vacuum at 600 ℃ for 30 min.The structures and magnetic properties of CoPt/BN multilayer films were investigated as a function of Ag layer thickness.It was found that the face-centered tetragonal (fct) (001) texture of CoPt was improved greatly by introducing the Ag toplayer or sublayer together with an Ag underlayer.Good (001)-oriented growth,low intergrain interactions as well as...     

花状自组装FePt纳米颗粒的制备

选用硼氢化钠(NaBH4)作为还原剂,聚乙二醇(PEG2000)作为表面活性剂,利用简单的湿化学还原工艺,在室温下制备花状自组装的FePt纳米颗粒。XRD和TEM表征显示:所制备的FePt纳米颗粒是化学无序的面心立方(fcc)结构。颗粒形貌主要由平均粒径分别为19.2和4.9nm的梭形和球形颗粒组成。这些梭形的"花瓣"和球形的"花蕊"自组装形成大小不等的花状结构。推测认为,纳米颗粒的花状自组装主要是表面活性剂集合的结果。VSM显示所制备FePt纳米颗粒的磁性能室温下为超顺磁性,饱和磁化强度Ms约为10.9(A·m2)/kg,相同条件下PVP作为表面活性剂时Ms约为0.6(A·m2)/kg,两者比较,选用PEG作为表面活性剂,Ms大约增大18倍。     

原位一步法合成Ag/Fe2O3磁性核壳纳米粒子

采用原位法在低温下一步合成Ag/Fe2O3磁性核壳纳米粒子,并采用XRD,TEM和UV光谱研究了Ag-Fe2O3核壳纳米复合材料的结构。结果表明,纳米银粒子表面被Fe2O3层包覆,Ag核的平均粒径大约为35nm,Fe2O3壳层平均厚度约为7.5nm或15nm,形成了核壳结构的电磁复合纳米粒子。在室温下,饱和磁化强度达到0.98(A·m2)·kg-1,矫顽力8.48×103A/m;Ag/Fe2O3核壳粒子的导电率达到0.62S/cm。通过此法可以比较容易的控制核和壳的尺寸以及复合粒子的单分散性,并得到较高的产率,在催化剂、医药、光电等领域有着广阔的应用前景。     

Micromagnetic simulation of Au interlayer in L1_0-FePt nanocomposite recording medium

Owing to the epitaxial inducement of Au atom,Au interlayer was introduced to increase the perpendicular anisotropy and the coercivity in L1_0-FePt nanocomposite film.Micromagnetics can be used to reveal the relationship between microstructure and magnetic properties of materials,and give the information of the perpendicular anisotropy and coercivity.In this work,the effect of the Au interlayer on annealed[Fe(0.5 nm)/Pt(0.5 nm)/Au(d nm)]_(10) nanocomposite recording medium by a micromagnetic model was studied.The model contains three phases:hard magnetic phase,soft magnetic phase,and nonmagnetic phase.The calculated result shows that perpendicular orientation degree of the texture and proportion of a hard magnetic phase to the total phase in the annealed film are both enhanced by increasing Au interlayer thickness.This result can be conducive to the improvement of the perpendicular anisotropy and the coercivity of the FePt nanocomposite film in the experiments.     

Electrodeposited Ni,Fe,Co and Cu single and multilayer nanowire arrays on anodic aluminum oxide template

The Ni, Fe, Co and Cu single and multilayer nanowire arrays to make perpendicular magnetic recording media were fabricated with nanoporous anodic aluminum oxide (AAO) templates from Watt solution and additives by the DC electrodeposition. The results show that the diameters of Ni, Fe, Co and Cu single and multilayer nanowires in AAO templates are 40–80 nm and the lengths are about 30 μm with the aspect ratio of 350–750. The magnetic properties of the prepared nanowires are different under different electrodepositing conditions. The remanences (B_r) of Ni/Cu/Fe multilayer nanowires are lower than those of others multilayer nanowires, and coercivity (H_c) of Ni/Cu/Fe multilayer nanowires are lower than those of others multilayer nanowires. These are compatible with the required conditions of high density magnetic media devices that should have the low coercivity to easily success magnetization and high remanence to keep magnetization after removal of magnetic field.     

Magnetization arrangement of hard magnetic phases and mechanism of magnetization and reversal magnetization of nano-composite magnets

During the process of directional solidification, laser remelting/solidification in the layer on sintered magnets, die-upsetting of cast magnets, or die-upsetting of nano-composites, the arrangements of the easy-magnetization-axes of the hard magnetic phases (Nd₂Fe₁₄B, SmCo₅ or Sm₂Co₁₇ type) in their designed directions have been studied. In Fe-Pt nano-composite magnets, attempts have been taken to promote phase transformation from disordered, soft magnetic A1 to ordered, hard magnetic L1₀ FePt phase at reduced temperatures. The dependence of the magnetization and reversal magnetization processes on the microstructures, involving the morphology and three critical sizes of particles of the FePt nano-composite magnets, are summarized. With the decrease of the nominal thickness of the anisotropic FePt film epitaxially grown on the single crystal MgO (001) substrate, the reversal magnetization process firstly changes from full domain wall displacement to partial magnetic wall pinning related to the morphology change, where the coercive force increases abruptly. The reversal magnetization process secondly changes from magnetic wall pinning to incoherent magnetization rotation associated with the particles being below the first critical size at which multi-domain particles turn into single domain ones, where the coercive force is still increased. And the reversal magnetization mode thirdly changes from incoherent to coherent rotation referred to the second critical size, where the increase of the coercive force keeps on. However, when the particle size decreases to approach the third critical size where the particles turn into the supperparamagnetic state, the coercive force begins to decrease due to the interplay of the size effect and the incomplete ordering induced by the size effect. Meanwhile, due to the size effect, Curie temperature of the ultra-small FePt particles reduces.     

Study on magnetization reversal of perpendicular recording media by in-field MFM observation

In-field MFM observation technology was employed to study the perpendicular recording medium under various perpendicular magnetic fields. A magnetization reversal field (H_R) map method was performed to reveal the magnetization reversal behavior of the medium. Under low magnetic field, some specific areas firstly reversed at a random position and then these reversed areas grew up. Under a high magnetic field, the magnetization reversal process tended to occur at the boundary between the reversed area and the non-reversed area. The simulation results implied that the long-range spatial interaction exists in the real media, which results in the bigger magnetic cluster. A simple experimental method was first proposed to estimate activation volume. The experimental activation volume agreed with the result calculated by the dynamic coercivity method.     

2004-2005年金属磁性功能材料研究新进展

本综述性论文开始写于1995年,其后每年撰写。本年综述的内容包含：（1）FePt薄膜磁性材料;（2）快淬的Pr-Fe—Co系磁性材料;（3）高饱和磁化强度薄膜磁性材料;（4）纳米磁性材料;（5）稀土磁性铁氧体。     

Controlling stress and diffusion for the low-temperature-ordering of L1<Subscript>0</Subscript> ordered FePt films

Low-temperature-ordering of L1₀ ordered FePt films have been extensively studied in recent years due to its potential for future application on magnetic perpendicular media. The predominant issue of the ordering process is the diffusion of iron and platinum atoms from a disordered to an ordered phase. The diffusion can be enhanced by adjusting diffusivity, providing extra energy, or reducing energy barriers. In addition to reducing the ordering temperature of FePt, (001)-oriented granular films require perpendicular media because the magnetic easy axis of the ordered phase is [001]. Atomic-scale multilayer deposition is proposed to achieve designed film structures.     

下一代高密度磁记录介质——L10FePt、CoPt研究进展

垂直磁记录是现今主要的信息存储技术.当前以CoCrPt为记录介质的垂直磁记录已达到密度极限,进一步提高记录密度需要采用磁晶各向异性能更高的材料.L10 FePt、CoPt被认为是下一代高密度磁记录的理想介质材料.本文系统综述了L10 FePt、CoPt记录介质的研究进展.     

Structural transformation of FePt nanocomposite films during annealing and its effects on magnetic properties

Fe100-xPtx(x=30at.%-60at.% ) nanocomposite films were deposited on natural-oxidized Si(100) substrates by magnetron sputtering. The as-deposited films were annealed between 373 and 1073 K. In situ X-ray diffraction shows that the FePt nanocomposite films undergo a phase transformation from a disordered FCC phase to an ordered L10 phase between 673 and 773 K. The coercivity is 306 kA·m-1 whiles the average grain sizes is about 10 nm in the optimized FePt alloy film sample annealed at 673K. The adjustable coercivity and fine grain size suggest that this FePt nanocomposites system is suitable as recording media at extremely high areal density.     

L1_0有序FePt薄膜的研究进展

L1_0有序FePt合金由于其极大的磁晶各向异性常数而成为下一代超高密度磁记录的候选材料,如何制备具有L1_0有序FePt薄膜成为近年来的研究热点。介绍了制备具有L1_0有序FePt薄膜的方法,包括选择合适的基底材料、单原子层沉积多层膜结构、引入下底层或中间层、添加合金元素或第三组元等,并阐述了这几种方法的主要特点和存在的问题,展望了今后FePt薄膜的发展方向。     

Accelerating disorder–order transitions of FePt by preforming a metastable AgPt phase

Many approaches had been reported to successfully reduce the transition temperature of FePt from A1 to L1₀ phase, though without detailed knowledge. In this work, we deposited the metastable AgPt layer adjacent to the Fe layer and addressed the importance of vacancies in the disorder–order transition of FePt at reduced temperatures on the basis of a kinetic diffusion model. The decomposition of the metastable AgPt phase, creating excess vacancies during the post-deposition annealing process, accelerated the intermixing between Fe and Pt and the nucleation of L1₀ FePt. The evolution of phase transformation from AgPt–Fe to L1₀ FePt–Ag was monitored by in situ high temperature X-ray diffractometry and was also validated by first-principles calculations. The intermixing between Fe and Pt and the nucleation of L1₀ FePt after annealing at 230 °C were directly observed by transmission electron microscopy and grazing incidence X-ray diffractometry, respectively. With the assistance of the decomposition of AgPt, we obtained a (0 0 1)-dominated L1₀ FePt film with an out-of-plane coercivity as large as 13.3 kOe after annealing at a temperature as low as 350 °C. The principles of the proposed method can be applied for versatile disorder–order phase transitions.