Structural and magnetic properties of RF sputtered FePt/Fe multilayers

Series of [FePt(4min)/Fe(t_Fe)]₁₀ multilayers have been prepared by RF magnetron sputtering and post-annealing in order to optimize their magnetic properties by structural designs. The structure, surface morphology, composition and magnetic properties of the deposited films have been characterized by X-ray diffractometer (XRD), Rutherford backscattering (RBS), scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDX) and vibrating sample magnetometer (VSM). It is found that after annealing at temperatures above 500 °C, FePt phase undergoes a phase transition from disordered FCC to ordered FCT structure, and becomes a hard magnetic phase. X-ray diffraction studies on the series of [FePt/Fe]_n multilayer with varying Fe layer thickness annealed at 500 and 600 °C show that lattice constants change with Fe layer thickness and annealing temperature. Both lattice constants a and c are smaller than those of standard ones, and lattice constant a decreases as Fe layer deposition time increases. Only a slight increase in grain size was observed as Fe layer decreased in samples annealed at 500 °C. However, the increase in grain size is large in samples annealed at 600 °C. The coercivities of [FePt/Fe]_n multilayers decrease with Fe layer deposition time, and the energy product (BH)_max reaches a maximum in the samples with Fe layer deposition time of 3 min. Comparison of magnetic properties with structure showed an almost linear relationship between the lattice constant a and the coercivities of the FePt phase.     

As-grown preparation of FePt-ordered alloy thin films from Pt/Fe bi-layered structure

A novel method to fabricate FePt-ordered alloy thin films with (0 0 1) preferential orientation from Pt/Fe bi-layered films has been developed. It is able to omit post-annealing with a furnace, and the whole process can be conducted in a chamber without exposing samples to air. In this method, the inter-diffusion and the hetero-epitaxial relation between Fe and Pt are key factors to attain an FePt-ordered alloy thin film with (0 0 1) preferential orientation. An FePt-ordered alloy thin film with (0 0 1) preferential orientation fabricated from Pt[3 nm]/Fe[3 nm] bi-layer employing this method exhibited a relatively large coercivity of 5.6 kOe and high squareness ratio of 0.94 on perpendicular magnetization property. This novel method has a potential to fabricate FePt-based perpendicular magnetic recording media more easily than several conventional methods.     

Low-temperature deposition of L10 FePt films for ultra-high density magnetic recording

A method based on strain-induced phase transformation was used to lower the ordering temperature of FePt films. The strain resulted from the lattice mismatch between the FePt film and the substrate or underlayer favored the ordering. The relationships between the lattice mismatch, the ordering of FePt film, and the corresponding magnetic anisotropic constant were investigated. A critical lattice mismatch near 6.33% was believed to be most suitable for improving the chemical ordering of the FePt films. CrX (X=Ru, Mo, W, Ti) alloys with (2 0 0) texture was used to control the easy axis and ordering temperature of FePt films on glass substrate. Large uniaxial anisotropy constant K_u?1×10⁷ erg/cm³, good magnetic squareness (∼1) and FePt(0 0 1) texture (rocking curve −5°) were obtained at the temperature T_s?250 °C when using CrRu underlayer. The diffusion from overlying layers of Ag and Cu and an inserted Ag pinning layer were effective in reducing the exchange decoupling and changing the magnetization reversal. The media noise was effectively reduced and the SNR was remarkably enhanced when a 2 nm Ag was inserted.     

L10-ordered high coercivity (FePt)Ag-C granular thin films for perpendicular recording

We report (FePt)Ag-C granular thin films for potential applications to ultrahigh density perpendicular recording media, that were processed by co-sputtering FePt, Ag, and C targets on MgO underlayer deposited on thermally oxidized Si substrates. (FePt)_1−xAg_x-yvol%C (0<x<0.2, 0<y<50) films were fabricated on oxidized silicon substrates with a 10 nm MgO interlayer at 450^oC. We found that the Ag additions improved the L1₀ ordering and the granular structure of the FePt-C films with the perpendicular coercivity ranging from 26 to 37 kOe for the particle size of 5-8 nm. The (FePt)_0.9Ag_0.1-50vol%C film showed the optimal magnetic properties as well as an appropriate granular morphology for recording media, i.e., average grain size of D_av=6.1 nm with the standard deviation of 1.8 nm.     

Granular L10 FePt (0 0 1) thin films for Heat Assisted Magnetic Recording

Granular L1₀ FePt (0 0 1) thin films were deposited on a Si substrate with Ta/MgO underlayers by rf sputtering. The effects of in-situ heating temperatures (350-575 °C), pressures (2-40 mTorr), and sputtering powers (15-75 W) on texture and microstructure were investigated for the FePt films. We obtained films with grain densities approaching 50 teragrains per in.², grains sizes down to 2.2 nm with center-to-center spacing of 4.2 nm and coercivity of 24 kOe. The order parameters for the L1₀ FePt thin films were derived and calculated to be as high as 0.91. Although the grain size is small, the spacing between grains is too large for practical heat assisted magnetic recording media. To reach the desired results, we propose that layer-by-layer growth should be promoted in the FePt layer by inserting another underlayer that provides a better lattice match to L1₀ FePt.     

Magnetic properties and static-dynamic magnetostrictive characteristics for SmFe2/Fe exchange-coupled multilayers

Giant magnetostrictive SmFe₂/Fe exchange-coupled multilayers were fabricated by ion beam sputtering deposition on glass substrates. The effects of SmFe₂/Fe exchange coupling action and vacuum annealing on soft-magnetic property and static-dynamic magnetostrictive characteristics of SmFe₂/Fe multilayers were investigated. The results showed that the soft-magnetic, static-dynamic magnetostrictive characteristics were greatly improved by SmFe₂/Fe exchange coupling action and proper vacuum annealing treatment temperature. Compared with that of SmFe₂ single film, the coercivity in the direction of easy magnetization axis for SmFe₂/Fe exchange-coupled multilayers exhibited a greater decrease. Better soft-magnetic properties were achieved (H_c=2.54 kA/m, M_s=120.38 emu/g, and M_r/M_s=0.21) after vacuum annealing at certain temperature. The magnetostrictive coefficient for SmFe₂/Fe exchange-coupled multilayers was about 135 ppm at 16 kA/m magnetic field. At first order resonant frequency (99.2 Hz), the amplitude peak-peak value for the as-deposited SmFe₂/Fe exchange-coupled multilayers was 46 μm. After the vacuum annealing treatment at 250 °C, the amplitude peak-peak value increased to 650 μm.     

Electric and thermo spin transfer torques in Fe/Vacuum/Fe tunnel junction

We present first-principle calculations of electric and thermo spin transfer torques (STT) in Fe/Vacuum(Vac)/Fe magnetic tunnel junctions (MTJs). Our quantitative studies demonstrate rich bias dependence of STT and tunnel magneto resistance (TMR) behaviors with respect to the interface roughness. Thermoelectric effects in Fe/Vac/Fe MTJs is remarkable. We observe larger ZT of 6.2 in 8 ML clean Vacuum barrier, where the heavily restrained thermal conductance should be responsible for. Thermo-STT in Fe/Vac/Fe MTJs show same order as that in Fe/MgO/Fe MTJs with similar barrier thickness.     

成分和厚度的依赖

通过调整Mn的成分，系统地研究了Ni81Fe19/Ni100-xMnx双层膜的磁学性质，特别是交换偏置场(Hex)的变化.当Ni100-xMnx中Mn的原子百分比在534%到600%之间时，对于150nm的Ni81Fe19，得到了最大的交换偏置场175kA/m，同时由于Mn对Ni81Fe19层的扩散所造成的磁矩的降低小于20%；高角x射线衍射证明Ni100-xMnx的晶格常数随着Mn成分的改变而变化，Mn含量越多，其晶格常数越大；制备态Ni100-xMnx膜晶格常数与θ相NiMn膜晶格常数的接近程度与NiMn膜θ相形成的容易程度相对应.也研究了交换偏置场随着Ni１００-xMnx厚度的变化，第一次得到了当Ni100-xMnx中Mn的原子百分比为706%时，Ni81Fe19(150nm)/Ni100-xMnx(90nm)双层膜在经过240℃，5h退火后，可以有80kA/m的交换偏置场，此时铁磁层磁矩的大小几乎不变. 关键词： Ni81Fe19/Ni100-xMnx 交换偏置场     

Effects of Fe－Fe bond length change in NaZn13-type intermetallic compounds on magnetic properties and magnetic entropy change

In this paper the effects of Fe－Fe bond length change on magnetic properties and magnetic entropy change have been investigated on LaFe_{12.4-x}Si_xCo_{0.6} and LaFe_{12.3-x}Al_xCo_{0.7} intermetallic compounds. According to the analyses of Fe－Fe bond length change, the variation of Curie temperature and the unusual magnetic phase transition which results in the large magnetic entropy change were explained. The effects of the substitution of Co and Si for Fe on magnetic entropy change and field-induced itinerant-electron metamagnetic transition in LaFe_{12.4-x}Si_xCo_{0.6} compounds were also studied and the considerable magnetic entropy change has been achieved.     

Fe/FeO/FeS混合物的Hugoniot线研究

 在50～210 GPa的压力范围内,用二级轻气炮和电探针技术对平均密度ρ₀＝(6.69±0.06) g/cm³的三组元Fe/FeO/FeS（质量分数分别为58.96%、35.83%、5.21%）混合物的Hugoniot线进行了实验测量,所得的Hugoniot参数为：C₀＝(3.97±0.07) km/s,λ＝1.58±0.03。该混合物Hugoniot线的实测结果与用体积可加性原理计算得到的相同组分混合物的Hugoniot线的符合性很好;根据实验数据还计算了混合物的0 K等温压缩线,发现它与体积可加性原理对单质Fe、FeO和FeS的0 K等温压缩线的计算结果相一致,证明了实验结果的合理性与体积可加性原理的适用性,也表明了此混合物在冲击压缩过程中没有发生过可察觉的化学反应。研究结果亦为今后对外地核各种浓度比Fe-O-S体系候选组分高温高压物态方程及物性的进一步研究奠定了基础。     

Magnetization temperature dependence in Fe/Cr superlattices

We report the temperature dependence of the saturation magnetization, M_s(T), of Fe(t)/Cr(40 Å) superlattices grown on MgO(1 0 0) and MgO(1 1 0) and its variation with Fe-layer thickness (5 Å<t<80 Å). The structure was characterized by X-ray diffraction. M_s(t) vs. T, as measured by DC magnetization and ferromagnetic resonance, show a large interface effect. The origins of this effect are discussed.     

Iron Species Present in Fe/ZSM-5 Catalysts – Influence of the Preparation Method

The Fe species present in Fe/ZSM-5 catalysts prepared by ionic exchange in aqueous solution or in the solid state are investigated. The samples were characterized by XRD, EPR, Mössbauer Spectroscopy (MOS-S) and chemical analysis. XRD showed that the peak intensity decreased with the increase in Fe content in the samples. EPR and MOS-S showed that the Fe atoms in all the activated samples appear as Fe⁺³, independently of the method used in the catalyst preparation. The MOS-S data also showed that Fe/ZSM-5, prepared by ion exchange in the solid state presented lower hematite content and more Fe species in charge-compensation sites, the responsible for the catalytic activity, as confirmed by the behavior in the propane oxidation.     

用于双色全息存储（Fe，Cu）：LiNbO3晶体的参量优化计算

在确定Cu在LiNbO3晶体中对应于365nm和633nm的激发系数、复合系数、光伏系数的基础上，采用龙格-库塔（Runge-Kutta）数值方法理论研究了双掺杂（Fe，Cu）：LiNbO3晶体的深浅能级的掺杂组分比、氧化-还原状态对双色全息存储的记录灵敏度和动态范围的影响，并探讨了同时取得尽可能大的灵敏度和动态范围的晶体条件。结果表明，为了同时得到较大的记录灵敏度和动态范围，在实际应用中选用浅能级掺杂浓度为5．0×10^25m^-3，深能级掺杂浓度为3×10^24～3×10^25m^-3之间的弱氧化晶体是合适的。     

Magnetic phase transition in (Fe,Mn)65Ni35 alloys

Magnetization measurements on the Fe₆₀Mn₅Ni₃₅ and Fe₅₀Mn₁₅Ni₃₅ alloy samples were carried out in the temperature range 80T300 K and in magnetic fields up to 8 kOe. The Fe₆₀Mn₅Ni₃₅ was found to order ferromagnetically with a Curie temperature, T_c, above 300 K. From the temperature dependence of the spontaneous magnetization, M_s, it was concluded that the magnetic behavior of Fe₆₀Mn₅Ni₃₅ follows Wohlfarth theory of weak itinerant ferromagnet. The Fe₅₀Mn₁₅Ni₃₅ sample exhibits a magnetic phase transition from ferromagnetism to paramagnetism at T_c=242 K. The critical amplitudes and critical exponents (β, γ and δ) have been determined by using Arrott plots, Kouvel–Fisher method and scaling plots of the reduced magnetization and reduced magnetic field. The values of β, γ and δ are discussed and compared with the results obtained for various theoretical models and also with the experimentally determined values for related systems obtained by others.     

The effect of thickness and annealing condition on the microstructure and magnetic properties of Fe/Pt multilayer thin films

[Fe(0.5 nm)/Pt(0.5 nm)]₄₀, [Fe(1 nm)/Pt(1.5 nm)]₂₀ and [Fe(3 nm)/Pt(3 nm)]₁₀ multilayer were prepared by DC magnetron sputtering. By conventional furnace annealing (CA) at 270–600 °C for various time, all of the films still remained the disordered structure with the soft magnetic phase. By rapid thermal annealing (RTA) at 500 °C for various time, we obtained the [Fe(1 nm)/Pt(1.5 nm)]₂₀ and [Fe(3 nm)/Pt(3 nm)]₁₀ films with L1₂ ordered FePt₃ phase which was almost ferromagnetic at room temperature. However, the [Fe(0.5 nm)/Pt(0.5 nm)]₄₀ films was still disordered state even under RTA. Compared with CA, RTA exposed an outstanding effect on accelerating the phase transition when the film thickness is over [Fe(0.5 nm)/Pt(0.5 nm)]₄₀.     

Study of near-infrared nonvolatile two-center holographic recording in LiNbO3:Fe:Rh crystal

The near-infrared nonvolatile holographic recording has been realized in a doubly doped LiNbO₃:Fe:Rh crystal by the traditional two-center holographic recording scheme, for the first time. The recording performance of this crystal has been investigated by recording with 633 nm red light, 752 nm red light and 799 nm near-infrared light and sensitizing with 405 nm purple light. The experimental results show that, co-doped with Fe and Rh, the near-infrared absorption and the photovoltaic coefficient of shallow trap Fe are enhanced in this LiNbO₃:Fe:Rh crystal, compared with other doubly doped LiNbO₃ crystals such as LiNbO₃:Fe:Mn. It is also found that the sensitizing light intensity affects the near-infrared recording sensitivity in a different way than two-center holographic recording with shorter wavelength, and the origin of experimental results is analyzed.     

Fe/Si多层膜的层间耦合与界面扩散

对以本征Si及重掺杂ｐ型和ｎ型Si作为中间层的Fe/Si多层膜的层间耦合进行研究，并通过退火，增大Fe，Si之间的扩散，分析界面扩散对层间耦合的影响. 实验结果表明，层状结构良好的制备态的多层膜，Fe，Si之间也存在一定程度的扩散，它是影响层间耦合的 主要因素，远远超过了半导体意义上的重掺杂，使不同种类的Si作为中间层的层间耦合基本 一致.进一步还发现，在一定范围内增大Fe，Si之间的扩散，即使多层膜的层状结构已经有了相当的退化，Fe/Si多层膜的反铁磁耦合强度基本保持不变. 关键词： Fe/Si多层膜 层间耦合 界面扩散     

An estimation of the magnetic disorder at Fe/Cr interfaces in coupled and non-coupled Fe/Cr multilayers

The antiferromagnetic coupling at the Fe/Cr interfaces, inferred from the orientation of the Cr magnetic moments, is used to estimate the magnetic disorder resulting from the interfacial roughness in Fe/Cr multilayers. A crossover from in-plane to out-of-plane orientation of Cr moments depends on the energy cost in either case: (i) to break the interfacial Fe–Cr antiferromagnetic coupling or (ii) having sites with frustrated Cr–Cr antiferromagnetic coupling in the Cr interlayers. A quantitative model of the magnetic frustration due to interfacial disorder in Fe/Cr multilayer systems is described. The step edge density, or terrace size, required to break the interfacial Fe–Cr coupling and destroy the Fe–Fe interlayer exchange coupling is estimated.     

Fe/Si薄膜中相干声学声子的光激发研究

本文通过抽运-探测技术, 利用飞秒激光脉冲激发并探测了Fe/Si薄膜中的高频相干声学声子. 通过经典的阻尼谐振函数, 对声学声子的动力学行为进行了拟合. 实验及拟合结果表明, 该声学声子的共振频率约为0.25 THz, 其退相时间约为12 ps, 且都与激发光的波长和能量密度无关. 声学声子的振幅随着激发光能量密度的增加而线性地增强. 临界参数12_τe-ph/T约为0.6, 表明相干声学声子的驱动力主要来源于电子热应力的贡献. 最后, 结合薄膜的厚度和质量密度, 可以得到室温下垂直于该Fe/Si薄膜表面(out of plane) 的弹性常数C_⊥约为283 GPa.     

Ru-O/Ru hybrid type of underlayer for CoPtCr-SiO2 perpendicular recording media on flexible tape

Ru/CoPtCr-SiO₂ bilayer prepared at 4 and 26 mTorr of Ar gas pressure for the deposition of Ru and CoPtCr-SiO₂ layers, respectively, exhibits better magnetic properties suitable for perpendicular magnetic recording media when they are deposited at room temperature on a Pt seed layer prepared at 450 °C. The Ru-O seed layer fabricated by a reactive sputtering method improves the Ru (0 0 1) texture deposited on a Ru-O layer. The Ru-O/Ru hybrid type of underlayer causes the improvement of the c-axis orientation of CoPtCr crystallites in the CoPtCr-SiO₂ layer deposited on it. Fine granulation of magnetic grains in the CoPtCr-SiO₂ layer is also attained when they are deposited on the Aramid type of flexible tape substrates.