Co—Nb／Cr磁性多层膜的振荡耦合

Ｃｏ－Ｎｂ－Ｃｒ磁性多层膜由高频溅射方法制得,由振动样品磁强计测量样品的磁性能。在２．６７Ｐａ溅射氩气压下,发现样品随Ｃｆ层厚度增加,铁磁层间出现铁磁性和反铁磁性的耦合振荡,饱和磁化强度Ｍｓ基本保持不变,而在０．６７Ｐａ溅射氩气压下,样品的饱和磁化强度Ｍｓ发生了振荡,这可能与春铁磁层中顺磁分量振荡变化有关。     

Co/Pt multilayer-based pseudo spin valves with perpendicular magnetic anisotropy

Pseudo spin valves(SVs) exhibiting perpendicular magnetic anisotropy were prepared by magnetron sputtering. Magnetization measurements of the Co/Pt multilayers were performed to select the reference and free layers. The selection criteria are square magnetic hysteresis loops, weaker current shunting effect, and proper coercivity. The optimal reference layer and free layer are Pt(5.0 nm)/[Co(0.4 nm)/Pt(0.6 nm)]3/Co(0.4 nm)/Cu(3.0 nm)and Cu(3.0 nm)/[Co(0.4 nm)/Pt(1.5 nm)]4, respectively.The resulting pseudo SV exhibits two well-separated hysteresis loops when the field is applied perpendicular to the film plane. The minor hysteresis loop corresponding to the free layer shifts toward negative direction of the magnetic field axis, indicating ferromagnetic interlayer exchange coupling between the two magnetic layers. The coupling also enhances the coercivity(HC) of both layers. The perpendicular giant magnetoresistance(GMR) of 2.7 % is achieved with current in plane measurement. The GMR first increases when Pt seed layer is thickened, reaches a maximum of 3.0 % at 4 nm and then decreases with the further increase of thickness. But thicker Cu spacer layer always lowers the GMR of the SV.     

Resonance modes of two-layer exchange-coupled ferromagnetic film

Ferromagnetic and spin-wave resonances in two-layer exchange-coupled ferromagnetic films have been investigated numerically at different intensities of a magnetic field when it is directed in parallel or perpendicular to the film plane. Layers of the film have finite thicknesses and possess anisotropy of the easy-plane and easyaxis types. It has been shown that at a nonzero parameter of interlayer exchange coupling the dynamic component of magnetization upon ferromagnetic resonance is distributed nonuniformly across the film thickness. Its change has been described when the external magnetic field decreases from the saturating field to zero.     

Effects of Cr interlayer on mechanical and tribological properties of Cr-Al-Si-N nanocomposite coating

Cr-Al-Si-N coatings were deposited on SUS 304 substrate by a hybrid coating system. A Cr interlayer was introduced between Cr-Al-Si-N coating and SUS 304 substrate to improve the coating adherence. The effects of Cr interlayer on the microhardness, adhesion, and tribological behavior of Cr-Al-Si-N coatings were systematically investigated. The results indicate that the microhardness of the Cr-Al-Si-N coatings gradually deceases with increasing thickness of Cr interlayers. The adhesion between Cr-Al-Si-N and SUS 304 substrate is improved by addition of the Cr interlayers. A peak critical load of ～50 N is observed for the coating containing Cr interlayer of 60 nm as compared ～ 20 N for the coating without Cr interlayer. The thicker Cr interlayers result in reduced critical load values. Moreover, the wear resistance of the Cr-Al-Si-N coatings is greatly enhanced by introducing the Cr interlayer with thickness of 60 nm in spite of the decreased microhardness. The friction coefficient of the coating system is also moderately reduced.     

Exchange bias in Cr/Gd multilayers with TC < TN

We report on the exchange bias phenomenon in Cr/Gd multilayers in which the Curie temperature (T_C) of the ferromagnetic Gd is slightly less than the Néel temperature (T_N) of the antiferromagnetic Cr. The exchange bias field H_E and the coercivity H_C of the samples display unusual temperature dependence behaviors in comparison with those of the traditional antiferromagnet (AFM)/ferromagnet (FM) multilayers with T_C > T_N. It is shown that the temperature dependence of H_E and H_C relates to the thickness of the Cr interlayer. For [Cr(20.4 nm)/Gd(18 nm)]₅ multilayers, the ferromagnetic behavior and exchange bias phenomenon persist to T > T_N; Oscillatory H_E and non-monotonic H_C with the temperature are observed. The anomalous temperature dependence of H_E and H_C results from the spin-density wave spin structure of the Cr layer and the non-collinear coupling between the Cr and Gd layers at the interfaces.     

Magnetic properties of Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> nanoparticles in carbon nanotubes

The interlayer coupling in an Fe/Cr/Fe layer system with wedge-type chromium spacers was investigated as a function of the chromium-layer thickness and temperature using Kerr magnetometry. The system with a moderate roughness demonstrates an interlayer coupling that can be well described in the framework of the biquadratic coupling model. The smoother sample shows interlayer coupling that can be described using both the biquadratic coupling and the proximity magnetism model proposed by Slonczewski.     

Phase diagram of magnetic structures in Fe/Cr/Fe films with nanoscale geometric inhomogeneities of interfaces

Results of an analysis of magnetic structures (mutual orientations of the iron-layer magnetizations) in three-layered Fe/Cr/Fe films formed due to the exchange interactions inside the layers of iron and chromium and on the Fe/Cr interfaces are given. The analysis was performed under the following assumptions: (1) the iron layers are ferromagnetic, and the magnetic structure of chromium layers has the form of transverse linearly polarized spin-density waves; (2) the iron-chromium exchange interaction is considered as a weak disturbance as compared to the exchange interactions inside the iron and chromium layers; therefore, they were considered as first-order and second-order perturbation-theory corrections; (3) the relative value of these corrections depends on the degree of roughness of the Fe/Cr interfaces; it was assumed that the roughness has a nanometer scale. With such approximations, the mutual orientation of the magnetizations of iron layers can be parallel, antiparallel, or noncollinear. The limits of stability of these structures depending on the thickness of the chromium interlayer and on the ratio of the first-to-second-order corrections have been determined. The main attention was paid to the conditions of the loss of stability with respect to changes in the phase of the spin-density wave, which can result in jumps in the curves of magnetization and magnetization reversal of the Fe/Cr films.     

High-frequency properties of two-layer exchange-coupled ferromagnetic structures

A numerical study of peculiarities of ferromagnetic resonance (FMR) in a two-layer exchange-coupled ferromagnetic structure has been performed at various magnitudes and directions of an external magnetic field. The layers have a finite thickness and are characterized by an anisotropy of the easy-plane or easy-axis type. The FMR frequencies have been found to decrease relative to the frequencies calculated in the model of an infinitely thin film. It has been demonstrated that with an increase in the layer thickness the direction of the displacement of the lower FMR mode depends on the magnitude and direction of the external magnetic field and that the frequency of the higher mode decreases at any direction of the external field. The amplitudes of the resonance curves decrease with increasing magnetic field, with the ratio of the half-width of the resonance curve to the resonance frequency decreasing up to the saturation point, after which this parameter varies only slightly. The FMR frequencies have been studied as a function of the constant of the interlayer exchange interaction for fields located in the saturation region.     

Crystal structure and magnetic properties of Fe/Cr/Gd superlattices

Results of investigations of structural and magnetic properties of Fe/Cr/Gd superlattices that differ in the thicknesses of the Cr interlayer have been reported. The insertion of the Cr interlayer between Gd and Fe layers has been found to lead to structural changes in Gd layers and the appearance of an additional fcc phase in them along with the main hcp phase. The new fcc phase is uniformly distributed across the thickness of the layer and is not localized near layer boundaries or in the center of Gd layers. Polarized-neutron reflectometry was used to show that the aforementioned structural changes are accompanied by a substantial (two-fold to threefold) decrease in the average magnetization of gadolinium over a wide temperature range. Near interfaces of the Gd layer, a layer appears that is two-to-three monatomic layers thick and characterized by increased magnetic moment.     

Al2O3和Cr过渡层对Ag膜光学性质及其附着力的影响

研究了在玻璃基底上镀制Al2O3和Cr过渡层对Ag膜反射率及附着力的影响.分光光度计测试了Ag膜的反射率,结果表明,与Cr过渡层相比,Al2O3过渡层对Ag膜反射率的降低相对较小;而且,随着Al2O3厚度的增加,Ag膜的反射率先增大后减小.XRD与AES测试表明,引入Al2O3或Cr可明显细化Ag晶粒,减弱Ag膜(111)织构;Al2O3作过渡层时,Al原子向Ag层中扩散显著;而Cr作过渡层时,只有少量Cr原子扩散进入Ag层.因此,Al2O3作过渡层能显著增强薄膜与玻璃基体之间的附着力.     

Competition between interfacial and interlayer exchange couplings in Co/Cr2O3/Fe trilayers

The temperature dependence of competition between interlayer and interfacial couplings is observed at different temperatures in Co (3 nm)/Cr₂O₃ (t)/Fe (10 nm) trilayers with t = 3 nm, 6 nm, 15 nm and 25 nm, respectively. The interlayer coupling enhances and the interfacial coupling weakens with increasing temperature. The balanceable temperature between interfacial and interlayer couplings shifts to low temperatures with increasing spacer thickness. Furthermore, the competition between interfacial and interlayer couplings greatly affects the magnetotransport properties of the trilayers. The negative magnetoresistance and the minimum resistance corresponding to balanceable temperature are found in trilayers.     

气相沉积铁钇多层膜的磁学性能

研究了气相沉积技术制备的Fe/Y多层膜的磁学性能,试验结果表明,当多层膜中铁层厚度减少到1．4nm时,薄膜由铁磁性转变为超顺磁性;多层膜的饱和磁化强度随铁层厚度的减少和钇层厚度的增加而显著降低。     

The origin of stresses in magnetron-sputtered thin films with zone T structures

In order to understand the origin of the residual stress state in thin films and its thickness dependence, the structure–stress relation of magnetron-sputtered Cr and CrN layers with thicknesses ranging from 100 nm to 3 μm was investigated in detail. Based on correlations between the layer-thickness-dependent grain size, texture and morphology and the magnitude of the intrinsic and thermal components of the residual stress, a model is proposed that explains the origin of internal stresses of thin polycrystalline films with zone T structures. The model was further extended for the CrN/Cr dual-layer system, where the CrN top layer is epitaxially aligned with the underlying highly (2 0 0)-oriented Cr interlayer. It is shown for the first time that both the intrinsic and thermal stress components are thickness-dependent, which is associated with the layer microstructure.     

Adaption of graded Cr/CrN-interlayer thickness to cemented carbide substrates' roughness for improving the adhesion of HPPMS PVD films and the cutting performance

High Power Pulsed Magnetron Sputtering (HPPMS) techniques jointly with the deposition of a graded Cr/CrN-nanointerlayer on cutting inserts can increase the film adhesion and consequently the tool life. These improvements depend on the roughness of the employed cemented carbide substrates. The investigations described in the present paper intend to explain the effect of Cr/CrN-interlayer thickness and substrate roughness on the coating adhesion and cutting performance. To attain various roughnesses, the applied cemented carbide inserts were superficially treated. These treatments were grinding at a medium roughness level, or grinding with subsequent polishing for enhancing the surface integrity and finally, in all cases, micro-blasting by fine Al₂O₃ grains. After Ar-ion etching, graded Cr/CrN adhesive layers with different thicknesses were deposited by HPPMS technology on the variously pretreated substrates. Subsequently, an approximately 3 μm thick (Ti,Al)N film was deposited by HPPMS PVD on all used inserts. Rockwell C indentations and inclined impact tests were performed to assess qualitatively and quantitatively the films' adhesion. The cutting performance of the coated tools was investigated in milling of 42CrMo4 QT. FEM supported calculations of the developed stresses during the material removal process contributed in explaining the obtained tool wear results. In these calculations, the adhesion, dependent on the substrate roughness characteristics and on the adhesive interlayer thickness, was taken into account. The results revealed that the effectiveness of HPPMS adhesive graded Cr/CrN-nanointerlayer strongly depends on the substrate surface integrity and on the interlayer thickness. Thus, the film adhesion and consequently the cutting performance can be significantly improved if the interlayer thickness is adapted to the substrate roughness.     

Magnetic anisotropy of Co/Cu/Co nanocrystalline films upon magnetic annealing

The magnetic anisotropy of Co/Cu/Co films with the thickness of the copper spacer corresponding to the antiferromagnetic and ferromagnetic indirect exchange coupling between Co layers has been studied. The films deposited on naturally oxidized (111) Si single crystals were produced by magnetron sputtering. The films were annealed at 240°C. Such an annealing virtually neither changes the grain size nor leads to the mixing of layers; i.e., no disturbance of the coupling type between the cobalt layers takes place. Changes in the surface and induced magnetic anisotropy and in the effective energy of indirect exchange coupling have been studied upon annealing in the presence and absence of a magnetic field. It has been found that the shape of surface inhomogeneities in the films changes upon annealing in the magnetic field applied along the film plane, which substantially affects, the surface anisotropy. In the films characterized by antiferromagnetic coupling, the easy axis of magnetization is induced only in the magnetic fields exceeding the saturation field. The induced-anisotropy constant estimated theoretically agrees well with those determined experimentally.     

Ferromagnetic resonance in a two-layer exchange-coupled ferromagnetic film with a combined uniaxial and cubic anisotropy in the layers

Dynamic properties of ferromagnetic two-layer exchange-coupled (100) films with a combined cubic and uniaxial magnetic anisotropy of layers have been studied numerously upon the magnetization along the [100], [010], and [011] directions. The allowance for cubic anisotropy substantially affects the dependence of the frequencies of the ferromagnetic resonance on the field strength. Repeated changes in the localization of the ferromagnetic-resonance modes between the layers of the film have been found to occur with an increase in the strength of the magnetic field. At a certain relationship between the constants of the combined anisotropy for the directions [010] and [011], an increase in the field leads to a shift of the maximum of the dynamic-susceptibility distribution toward the interlayer boundary without a change in the localization of the modes.     

保温时间对TiAl合金与镍基合金扩散连接界面组织结构及连接强度的影响

采用纯钛箔做中间层扩散连接TiAl合金与镍基高温合金(GH99).利用扫描电镜、电子探针和X射线衍射等手段对界面产物及接头的界面结构进行分析.结果表明,GH99/Ti界面主要由四个反应层组成,分别为(Ni,Cr)ss,富Ti-(Ni,Cr)ss,TiNi和Ti2Ni.当保温时间较短时,Ti/TiAl界面反应层主要为Ti(Al)ss.延长保温时间,此界面反应层转化为Ti3Al和Al3NiTi2.随着保温时间的延长,TiNi反应层厚度持续增加,而Ti2Ni反应层厚度先增加后减小.随保温时间的延长接头的抗剪强度先增加后减小,然后又增加.由接头断口形貌可以看出,接头主要断裂于Ti2Ni反应层.     

The growth of carbon coating layers on iron particles and the effect of alloying the iron with silicon

Magnetic fine particles of metallic Fe coated with graphitic carbon layers were synthesized by annealing Fe₂O₃ particles with carbon powders at 1673 K in nitrogen atmosphere. For comparison, SiC was added to Fe₂O₃. X-ray diffraction measurement showed that the lattice constants of Fe changed depending on the Si contents. Mössbauer spectroscopy confirmed that Fe-Si alloys were formed by the Si addition and that the iron carbide disappeared. Electron microscope images revealed that the thickness of carbon coating layers increased from 24 nm to 36 nm as a result of the Si addition. Soaking tests showed that the corrosion resistance of the carbon-coated Fe particles was improved by the addition of Si. The results suggest that Si caused C to leave the Fe cores and move to the surface to form a carbon coating.     

金属Fe／Cu超晶格的结构和铁磁共振

用直流磁控溅射技术在玻璃衬底上制得了金属Fe/Cu超晶格薄膜。用X射线衍射和电子显微镜观察和分析了它们的调制特性和晶格结构;用铁磁共振(FMR)技术和振动样品磁强计进行了磁学性质的研究。新的实验结果揭示了在邻近Fe层间的耦合特性和它对超晶格磁性的影响。     

Exchange interactions and magnetic properties of intermetallic compounds

1　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｉｎｔｅｒｍｅｔａｌｌｉｃｃｏｍｐｏｕｎｄｓＲＭｎ2 Ｇｅ2 ｃｒｙｓｔａｌｌｉｚｅｉｎｔｈｅｂｏｄｙ ｃｅｎｔｅｒｅｄ ｔｅｔｒａｇｏｎａｌＴｈＣｒ2 Ｓｉ2 ｔｙｐｅｓｔｒｕｃｔｕｒｅ(ｓｐａｃｅｇｒｏｕｐｉｓＩ4 /ｍｍｍ) ,ｗｈｉｃｈｉｓｃｏｎｓｉｓｔｅｄｏｆＲ ,ＧｅａｎｄＭｎｌａｙｅｒｓ ,ｓｔａｃｋｅｄｉｎｔｈｅｓｅｑｕｅｎｃｅＲ Ｇｅ Ｍｎ Ｇｅ Ｒ ａｌｏｎｇｔｈｅｃ ａｘｉｓ[1] .Ｆｒｏｍｔｈｅｍａｇｎｅｔｉｃｐｏｉｎｔｏｆｖｉｅｗ ,ＲＭｎ2 Ｇｅ2 ｃｏｍｐｏｕｎｄｓｈ…