热分解法制备Bi替石榴石磁光薄膜的静态热磁模拟近似计算

对磁光薄膜进行热磁模拟可以了解影响热磁记录过程的各种因素及这些因素间的相互关系以及它们对写入信息的影响。采用近似计算方法对Bi、Al替DyIG磁光薄膜进行静态热磁模拟,得出在居里点写入的情况下写入点半径与定入功率、数值孔径、材料的反射率、材料的热导率及激光波长的关系。该方法为热磁定入过程提供了一种简捷的理论指导。     

静磁表面波对高斯光脉冲的衍射特性研究

研究了磁光薄膜波导中线性啁啾高斯光脉冲与单频连续静磁波共线作用,给出了水平磁化时基于静磁表面波的磁光耦合方程.分别采用解析法和数值法计算了1310 nm和1550 nm两种光波长入射时衍射光的压缩特性,两种求解方法得到的结果一致.计算表明,衍射光脉冲的半峰全宽(FWHM)随相位失配因子的频率变化率和啁啾系数的增大而减小;在给定的计算参数下,与1310 nm波长对应的衍射光脉冲具有较大的峰值强度,但1550 nm波长输入时可以获得更窄的衍射光脉冲,因而1550 nm光脉冲更适于作为磁光脉冲压缩的脉冲源.文章还分析了磁损耗对衍射光脉冲的光强和输出脉宽的影响,对于普通的磁光薄膜,损耗基本上不影响光脉冲压缩效果.     

C掺杂FePt铁磁薄膜光诱导超快退磁动力学研究

FePt合金薄膜由于具有较强的磁各向异性而在磁信息和磁光信息存储中具有重要的应用.C掺杂可精确调控薄膜的磁各向异性,从而可有效地改变薄膜的矫顽场.通过超短激光脉冲与铁磁薄膜相互作用,可以获得非平衡状态下电子、自旋和晶格等自由度之间的动态耦合参数,这是研究超快磁记录材料的物理基础.本文基于瞬态磁光Kerr效应,研究了两种C掺杂浓度下FePt薄膜的超快磁光响应.实验结果表明:瞬态Kerr信号与外加磁场正相关,磁场反向,Kerr信号反号,而瞬态反射率与外加磁场无关;不同C掺杂的FePt薄膜的矫顽场不同,软磁的退磁时间显著小于硬磁薄膜的退磁时间.我们还观测到超快激光在铁磁薄膜中诱导频率约为49 GHz的相干声学声子,该声子的频率与外加磁场无关.实验结果为设计和研制新型磁光薄膜提供了实验依据.     

磁性薄膜的晶格结构和磁性

采用Monte-Carlo模拟方法对六边形、正方形和三角形晶格结构磁性薄膜的磁学特性及磁畴结构进行了模拟,结果表明,磁性薄膜的磁性特征及其磁相变温度和薄膜结构密切相关并存在临界膜厚,当薄膜厚度大于临界膜厚时薄膜磁性特征稳定.在低温区,不同结构磁性薄膜的磁滞回线均出现台阶现象,结果同相关实验一致.     

HfO_2单层膜的吸收和激光损伤阈值测试

薄膜吸收是降低膜层激光损伤阈值的重要原因,为了研究薄膜吸收对激光损伤阈值的影响,对HfO2单层膜在1 064 nm处的吸收及其在不同波长激光辐照下的损伤阈值进行了测试和分析。研究结果表明:薄膜的激光损伤阈值由薄膜吸收平均值(决定于薄膜中缺陷的种类和数量)和吸收均匀性(决定于薄膜中缺陷的分布)共同决定;根据HfO2单层膜在1064 nm波长处的吸收值,不但可以定性判断薄膜在1 064 nm波长,而且还可以判断在其它波长激光辐照下的抗激光损伤能力。     

在半导体-金属相变温度附近氧化钒薄膜光学性质的异常变动

在可见光—近红外波段的不同波长下,测量了半导体-金属相变过程中氧化钒薄膜样品的反射率和透射率.在薄膜相变过程中,不同波段的反射率曲线和透射率曲线表现出不同的变化趋势.利用非相干光在薄膜中的多级反射-透射模型,计算了相变过程中不同波长下氧化钒薄膜的折射率n和消光系数k随温度的变化.结果表明,在相变温度附近氧化钒薄膜光学性质的异常变动,其原因既有薄膜的折射率和消光系数随波长的变化趋势不同,也有在吸收性薄膜中存在探测光多次反射和透射的累加效应.     

铁磁金属薄膜纳米点连接的各向异性磁电阻

首次运用电子束光刻技术和真空沉积技术在硅片表面制备了宽度在20纳米Ni80Fe20薄膜铁磁金属纳米点连接,通过对铁磁金属薄膜纳米点连接样品在不同温度下的磁电阻和I~V的研究,得出宽度在20纳米的铁磁金属薄膜纳米点连接中所观察到的磁电阻现象是各向异性磁电阻,其导电行为主要是金属导体导电行为,受量子化电导作用较小;通过对宽...     

基于深紫外激光-光发射电子显微技术的高分辨率磁畴成像

基于磁二色效应的光发射电子显微镜磁成像技术是研究薄膜磁畴结构的一种重要研究手段,具有空间分辨率高、可实时成像以及对表面信息敏感等优点.以全固态深紫外激光(波长为177.3 nm;能量为7.0 eV)为激发光源的光发射电子显微技术相比于传统的光发射电子显微镜磁成像技术(以同步辐射光源或汞灯为激发源),摆脱了大型同步辐射光源的限制;同时又解决了当前阈激发研究中由于激发光源能量低难以实现光电子直接激发的技术难题,在实验室条件下实现了高分辨磁成像.本文首先对最新搭建的深紫外激光-光发射电子显微镜系统做了简单介绍.然后结合超高真空分子束外延薄膜沉积技术,成功实现了L10-FePt垂直磁各向异性薄膜的磁畴观测,其空间分辨率高达43.2 nm,与利用X射线作为激发源的光发射电子显微镜磁成像技术处于同一量级,为后续开展高分辨磁成像提供了便利.最后,重点介绍了在该磁成像技术方面取得的一些最新研究成果:通过引入Cr的纳米"台阶",成功设计出FePt的(001)与(111)双取向外延薄膜;并在"台阶"区域使用线偏振态深紫外激光观测到了磁线二色衬度,其强度为圆二色衬度的4.6倍.上述研究结果表明:深紫外激光-光发射电子显微镜磁成像技术在磁性薄膜/多层膜体系磁畴观测方面具备了出色的分辨能力,通过超高真空系统与分子束外延薄膜制备系统相连接,可以实现高质量单晶外延薄膜制备、超高真空原位传输和高分辨磁畴成像三位一体的功能,为未来磁性薄膜材料的研究提供了重要手段.     

磁性液体薄膜的折射率在外加磁场作用下的变化特性研究

用两块玻璃夹持一层几个μm厚的磁性液体薄膜.将这一磁性液体薄膜垂直放置于由亥姆霍兹线圈建立的均匀磁场中.在迈克尔孙干涉仪上用对比测量法测量在不同外加磁场强度作用下磁性液体薄膜的折射率.实验发现, 磁性液体薄膜的折射率随外加磁场强度的变化而变化.结合实验研究, 提出了外加磁场改变了磁性液体颗粒链的大小, 改变了磁性颗粒链的大小和入射光波波长的比值, 从而改变了磁性液体的折射率的设想.初步建立起了磁性液体薄膜的折射率和外加磁场强度之间的关联式.为磁场测量、光学阀门等新型磁光器件的开发提供了新的技术.     

磁光光子晶体结构的法拉第效应增强

在超薄薄膜的基础上,基于时域有限差分法原理,利用FDTD Solutions仿真软件分别研究了基于两种多层膜结构和一种金属光栅结构的磁光光子晶体法拉第旋光效应。研究表明,多层膜结构的法拉第旋光效应增强原理为入射光在薄膜中心层的透射谱谐振,而金属光栅周期结构的法拉第效应增强是通过金属光栅激发表面等离子体实现的;在三种结构中,金属光栅周期结构具有更广的法拉第偏转角增强域。进一步通过参数优化,实现对金属光栅周期结构工作波长的可调节性研究,为薄膜型磁光器件设计提供了理论依据。     

Below-diffraction-limited hybrid recording using silicon thin film super-resolution structure

We report on new experimental results for below-diffraction-limited hybrid recording. In our experiments, by means of focused laser assisted magnetic recording, the magnetic domains within TbFeCo thin films are obtained under an external perpendicular direct magnetic field. For a single magnetic medium, the domain size is mainly determined by the focused spot, which is about 620~nm for the laser wavelength λ =406~nm, and a numerical aperture of the lens of 0.80. However, when a silicon thin film structure is inserted between the substrate and the magnetic medium, the recording domains can be reduced obviously. By optimizing the experimental condition, even the size can be reduced to about 100~nm, which is below the diffraction limit, i.e. about 1/6 of the spot size. This is very useful for improving the hybrid recording density in practical applications.     

Magnetic recording materials since 1975

When information is to be recorded and stored on a re-usable medium, magnetic recording, in one form or another, has been and is today the dominant technology. Magnetic particles or thin films having a coercivity of several hundred oersteds, are easily capable of retaining a magnetic pattern of recorded information (at densities of tens of thousands of bits/inch and track densities of thousands of tracks/inch) for hundreds of years and yet when desired, the pattern can be changed by simply writing the new information over the old. Since the recording process requires only a change in direction of the electron spins, the process is infinitely reversible and the new information may be read immediately with no development process being required. This paper deals with developments of the magnetic (and some important non-magnetic) properties of recording media that have occurred since 1975. It describes their current embodiment in particles of cobalt-modified iron oxides, chromium dioxide, barium ferrite and metals and in thin films of metals, alloys and oxides. The curious and currently unexplained aspects of the behavior of these important materials is noted.     

L1_0-FePt合金单层磁性薄膜的微磁学模拟

具有四方结构的L10-FePt合金因其具有高磁晶各向异性和良好的化学稳定性而成为超高密度薄膜磁记录介质的最佳选择.对实验制备得到的磁性能良好的垂直取向L10-FePt合金单层膜进行了微磁学分析.在传统微磁学模型的基础上,根据晶体的对称性,引入了四角磁晶各向异性能密度的唯象表达形式;又依据薄膜生长过程中晶格对称性的破坏,考虑了薄膜面内的应力,并引入了磁弹性能.以四角磁晶各向异性能和磁弹性能为重点,对L10-FePt合金单层膜的磁滞回线进行了详细的分析,并且用微磁学方法确定了薄膜面内应力的大小.     

Sputtered amorphous Co-Pt-P thin films for soft underlayer of perpendicular magnetic recording

In this paper, a novel amorphous Co-Pt-P thin film fabricated by DC sputtering was proposed for soft underlayer in perpendicular recording. The structural and magnetic properties of the films were investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM), respectively. The results show that maximum permeability of Co-12 at%Pt-P films sputtered at room temperature (RT) is quite low when the phosphorus content is less than 5.2 at%, but Co-12 at%Pt-7 at%P thin film, is of amorphous state and has a high permeability of ∼500. The excellent soft magnetic properties of maximum permeability (500), coercivity (18 Oe) and saturation magnetization (760 emu/cm³) indicate that the amorphous Co-12 at%Pt-7 at%P film is expected to be a promising soft magnetic underlayer of perpendicular magnetic recording. The Co-12 at%Pt-7 at%P thin film is gradually crystallized with increasing substrate temperatures. The crystallization temperature of the Co-12 at%Pt-7 at%P thin film is ∼200 °C.     

Magnetic properties and microstructure of CoCr and CoCrTa thin films sputtered at high pressure on a PET substrate

Thin magnetic films (CoCr/Cr, CoCrTa/Cr and CoCrTa/Cr/SiO) are deposited by DC-magnetron sputtering on a PET substrate. The optimum sputter pressure, giving rise to the highest coercive force, is found to be around 50 mTorr. However, the deposition parameters influence the value of this optimum pressure. The addition of Ta to CoCr leads to phase segregation, resulting in CoCrTa films in which the magnetic interaction between the grains is more dipolar than in CoCr films. The magnetic interactions in CoCrTa films are less dependent on the sputter parameters than those in CoCr films. The evaporation of a seedlayer of, e.g. SiO prior to the deposition of the Cr underlayer increases the coercive force of the CoCrTa thin films, especially when the CoCrTa layer is thinner than 50 nm. This makes these films more suitable for high-density magnetic recording.     

Thin film properties by facing targets sputtering system

In this study, film thickness distribution and c-axis crystalline orientation of deposited thin films were studied after preparing Co–Cr thin films, a promising ultra-high density perpendicular magnetic recording media, with a facing targets sputtering (FTS) apparatus. Electrical discharge characteristics needed for the optimum operation of sputter device was also studied in order to prepare thin films of superior c-axis crystalline orientation with FTS method (apparatus) in which thin film of fine quality can be formed because temperature increase of substrate due to the bombardment of high-energy particles can be restrained.As a result of the study, it is confirmed that the FTS method can give stable working under broad magnetic field and range of gas pressure and stable electrical discharge under low Ar gas pressure. Film thickness of prepared thin film shows fairy regular distribution and could obtain good thin films whose dispersion angle of c-axis crystalline orientation is about 3.5°.     

Ordering intermetallic alloys by ion irradiation: a way to tailor magnetic media

We show how, combining He ion irradiation and thermal mobility below 600 K, the transformation from chemical disorder to order in thin films of an intermetallic ferromagnet (FePd) may be triggered and controlled. Kinetic Monte Carlo simulations show that the initial directional short range order determines the transformation. Magnetic ordering perpendicular to the film plane was achieved, promoting the initially weak magnetic anisotropy to the highest values known for FePd films. Applications to ultrahigh density magnetic recording are suggested.     

Magnetic interactions in Co-based alloy thin films

The interactions in ternary and quaternary Co-based alloy thin films for longitudinal recording media, with different thickness, are studied. The analysis is performed through the measurement of the initial magnetization and ordinary hysteresis curves. The interactions result stronger in quaternary than in ternary alloy films and when the film thickness is smaller. These findings are discussed in relationship with the evolution of the magnetization switching, characterized by a tendency towards a more coherent rotation of the magnetization in single-domain grains of thinnest and quaternary films, owing to the complex structure of these films. The impact of this evolution on the thermal stability of the magnetic properties is also discussed.     

Magnetic tuning of biquadratic exchange coupling in magnetic thin films

The effective interlayer coupling between antiferromagnetically coupled hard and soft ferromagnetic thin films is investigated as a function of the magnetic bit length in the hard layer, which is controlled using a magnetic recording system. The interlayer coupling is explored by studying the magnetization reversal of the soft layer. As the bit length decreases, the coupling evolves from antiferromagnetic to biquadratic to uncoupled. These results are reproduced using a micromagnetic model and determine the applicability range of Slonczewski's fluctuation model of biquadratic coupling.     

Improvement of magnetic properties and read/write characteristics in SmCo5 perpendicular thin films

An SmCo₅ alloy is a promising candidate for ultra-high density magnetic recording media because of its strong uniaxial magnetocrystalline anisotropy, whose constant, K_u, is more than 1.1×10⁸ erg/cm³. Recently, we successfully obtained high perpendicular magnetic anisotropy for a sputter-deposited SmCo₅ thin film by introducing a Cu/Ti dual underlayer. However, it is necessary to improve magnetic properties and read/write (R/W) characteristics for applying SmCo₅ thin films to perpendicular magnetic recording media. In this study, we focused on reduction of magnetic domain size and change of a magnetization reversal process of SmCo₅ perpendicular magnetic thin films by introducing carbon (C) atoms into the constituent Cu underlayer. The magnetic domain size became small and the ratio of coercivity (H_c) against magnetic anisotropy (H_k) which is an index of the magnetization reversal process was increased by adding C atoms. We also evaluated the R/W characteristics of SmCo₅ double-layered media including C atoms. The medium noise was decreased and signal-to-noise ratio increased by introducing the C. The addition of C into the Cu underlayer is effective for changing the magnetization reversal process, reducing medium noise and increasing SNR.