稀土永磁薄膜材料

简要地介绍在纳米复合稀土永磁薄膜材料、各向异性稀土永磁薄膜材料方面的进展。在纳米复合稀土永磁薄膜材料中实现磁性交换耦合和剩磁增强效应，系统地研究了其结构与磁性的关系。制备成功高磁能积的各向异性稀土永磁薄膜材料，比较了Ti或Mo缓冲层对Nd-Fe-B薄膜的表面形貌、磁畴结构和磁性能的影响。发现薄膜的表面形貌强烈地依赖于缓冲层的厚度。由于它极大地影响薄膜的成分，溅射速率被证明是控制薄膜的显微结构、表面形貌和磁性能的一个重要因素。在微磁学模型的基础上，通过分析从5到300K的矫顽力温度依赖关系。研究了各向异性Pr-Fe-B薄膜的矫顽力机制。在晶粒表面，由于磁各向异性的降低和局域退磁场的提高导致的反转畴的形核被确定为控制各向异性Pr-Fe—B薄膜的磁化反转过程的首要机制。     

Experiments on the reflection of cold atoms from magnetic thin films

We report the results from a series of experiments in which ferromagnetic thin films were used as atom mirrors for laser-cooled rubidium atoms released from a magneto-optical trap. The thin films were made of cobalt and lanthanum calcium manganite (LCMO) with thicknesses between 20 and 300 nm. The magnetic domains in these thin films have a periodic structure where the spatial period is of the order of the thickness of the film, and the field decays exponentially above the film over a length scale comparable to the domain size. Thus, the neutral atoms reflect off these films from distances comparable to the thickness of the film, resulting in modification of the reflectivity due to the competition between the repulsive magnetic force and the attractive short-range forces such as van der Waals and Casimir forces. The smoothness of the atom mirror is also modified due to the proximity of the magnetic domains. The reflectivity is sensitive to the domain structure and size, which can be modified in LCMO by applying a modest external magnetic field. In this paper, we discuss the evaluation of the thin films as magnetic mirrors for atom optics, and the measurement of the van der Waals force with an accuracy of about 15%, using cobalt thin films. We also discuss some preliminary results on the temperature-dependent reflectivity for atoms near the ferromagnetic transition at 250 K in the LCMO film, and on the domain dynamics and relaxation.     

Short-range order in Valenta model of thin films

The present paper deals with the Valenta model for magnetic thin films extended to the entropy construction in its pair representation. The problem of the thin films theory is old, but the Valenta model introduced fifty years ago seems to be still an effective approach requiring however, some modifications. The most important one is connected with the improvement of the entropy construction in the self-consistent way when the correlations are taken into account. The idea is introduced in the present paper and discussed in detail.     

An in-situ study of structure and magnetic properties of Fe films on the sulphur passivated Ge(100) surface at 150°C

Ultra-thin Fe films have been grown on the sulphur passivated Ge(100) surface at 150°C. The growth, structure and the magnetic properties of the thin films were studied with LEED, AES, angle resolved AES and in-situ magneto-optical Kerr effect measurements. For the first five monolayers of Fe, no long-range order was observed . However, angle resolved AES data suggest that local order occurs with a small fraction of the Fe atoms adsorbed on bcc sites. For thicker Fe films, the growth becomes ordered. A comparison of the present study and with a previous study of the growth of Fe on sputter cleaned Ge(100)(2×1) surface, shows that sulphur passivation effectively prevents Fe–Ge intermixing. During the Fe deposition process, most of the sulphur atoms migrate to the growing surface, thus acting as surfactants. The presence of sulphur at the surface also affects the growth and magnetic properties of the thin films.     

Effect of organic additives on characterization of electrodeposited Co-W thin films

Co-W thin films were electrodeposited from aqueous bath with different organic additives. Electrochemical analysis showed that the transient state was limited and polarization behaviors were more evident during Co-W electrodeposition in the presence of organic additives. SEM measurement indicated that the surface morphology was affected by the nature of the organic additives to a large extent. Homogeneous Co-W thin films were obtained from the solutions containing ethyl methacrylate. Moreover, it was obvious that the presence of organic additives, in the electroplating bath, modified the structure and magnetic properties of the Co-W thin films according to the XRD and VSM measurements.     

外加磁场对磁控溅射制备氮化硅陷光薄膜的影响

在基底与靶材之间放置磁性强弱不同的永久磁铁来研究外加磁 场对磁控溅射制备氮化硅陷光薄膜的影响. 通过X射线衍射、原子力显微镜 (AFM) 以及紫外分光光度计分别测试了外加磁场前后所制备薄膜的组织结构、表面形貌和光学性能. 结果表明, 外加磁场后, 氮化硅薄膜依然呈现非晶结构; 但是表面形貌发生明显改变, 中心磁场1.50 T下, 薄膜表面为特殊锥状尖峰结构"类金字塔"的突起, 而且这些突起颗粒垂直于基底表面; 在 可见光及近红外范围内, 中心磁场1.50 T 下的薄膜样品平均透射率最大, 平均透射率达到90% 以上, 比未加磁场的样品提高了近1 倍, 具有很好的陷光特性. 关键词： 外加磁场 磁控溅射 氮化硅薄膜 陷光效应     

Swift heavy ion induced surface modifications in nano-crystalline Li-Mg ferrite thin films

The swift heavy ion (190 MeV Au¹⁴⁺) induced modifications in surface morphologies of the nanocrystals of ferrite thin films have been extensively studied through the images of atomic force microscopy (AFM). In most of the irradiated films significant features like, the ditch and dike structures, have been observed through out the surface. We try to explain the observed changes on the basis of thermal spike model followed by momentum transfer induced lateral mass transport. In addition to these changes some new and interesting features have been noticed after irradiation in 8F and 9F ferrite thin films. These new features are attributed to sputtering phenomenon due to the presence of defects like latent tracks.     

Distribution and magnetization of Co near the rutile TiO2 (110) surface: A first-principles study

The room-temperature ferromagnetism demonstrated by Co-doped TiO₂ films remains a challenge to our understanding, notwithstanding intensive experimental and theoretical investigations. We have calculated the binding energy and spin-polarization of Co atoms doped in the rutile TiO₂ (110) surface using first-principles method, aiming to elucidate the relationship between structure and magnetism of Co-doped TiO₂ films. In a defect-free surface the binding energy of Co substituting for Ti reduces slightly with the depth into the surface, suggesting a very minor Co depletion near the surface. More interestingly, the stability of ferromagnetic coupling over anti-ferromagnetic coupling of Co atoms decreases rapidly when it goes from surface to the bulk region. The residual ferromagnetism in the surface will give rise to a non-vanishing average magnetic moment of the thin film. The calculated pairing energy of Co is 0.12 eV/Co in the surface layer and 0.20 eV/Co in the middle layer of the film, an indication that Co atoms have a tendency to aggregate in both regions and that pairing will not modify the Co concentration in the direction vertical to the surface.     

Free-standing urethane/urea elastomer films undoped and doped with ferro-nano-particles

We report on an experimental study of the structures presented by urethane/urea elastomeric films without and with ferromagnetic nanoparticles incorporated. The study is made by using the X-ray diffraction, nuclear magnetic resonance (NMR), optical, atomic and magnetic force (MFM) microscopy techniques, and mechanical assays. The structure of the elastomeric matrix is characterized by a distance of 0.46nm between neighboring molecular segments, almost independent on the stretching applied. The shear casting performed in order to obtain the elastomeric films tends to orient the molecules parallel to the flow direction thus introducing anisotropy in the molecular network which is reflected on the values obtained for the orientational order parameter and its increase for the stretched films. In the case of nanoparticles-doped samples, the structure remains nearly unchanged although the local order parameter is clearly larger for the undoped films. NMR experiments evidence modifications in the molecular network local ordering. Micrometer size clusters were observed by MFM for even small concentration of magnetic particles.     

Sm–Co films for high-density magnetic recording media

In this experiment, Cr–Cu thin film was used as an underlayer for Sm–Co film. The magnetic properties and crystal structure of Sm–Co films prepared onto this kind of underlayer have been studied. Grain size and surface roughness have been reduced with the introduce of Cr. The Cr addition into the Cu underlayer also improves the c-axis orientation of Sm–Co films. As a result, films with squareness ratio as high as 0.95 and perpendicular coercivity as high as 12.3 kOe have been prepared.     

Ginzberg-Landau理论对超导薄膜的适用性

本文指出虽然三十年来Ginzberg-Landau理论(以下简称G-理论)被人们广泛地用于描述超导薄膜的临界场,而且它还是描述强耦合超导薄膜临界场的唯一理论,但G-L关于薄膜临界场的理论不仅一直未得到实验证明,而且它既不能用于描述结晶态的弱耦合超导薄膜的临界场,也不适用于描述强耦合超导薄膜的临界场。本文还提出了一个在薄膜极限下定域的新判据:ξ<<λ,ξ<关键词：     

Mechanical properties of sol-gel derived lead zirconate titanate thin films by nanoindentation

Lead zirconate titanate (PZT) thin films are deposited on platinized silicon substrate by sol-gel process. The crystal structure and surface morphology of PZT thin films are characterized by X-ray diffraction and atomic force microscopy. Depth-sensing nanoindentation system is used to measure mechanical characteristics of PZT thin films. X-ray diffraction analyses confirm the single-phase perovskite structures of all PZT thin films. Nanoindentation measurements reveal that the indentation modulus and hardness of PZT thin films are related with the grain size and crystalline orientation. The increases of the indentation modulus and hardness with grain size are observed, indicating the reverse Hall-Petch effect. Furthermore, the indentation modulus of (1 1 1)-oriented PZT thin film is higher than those of (1 0 0)- and random-oriented films. The consistency between experimental data and numerical results of the effective indentation moduli for fiber-textured PZT thin films using Voigt-Reuss-Hill model is obtained.     

The magnetization model of multilayered composite thin films: Beyond the effective-medium theories

Multilayered composites consisting of many thin ferromagnetic films with in-plane magnetic anisotropy separated by non-magnetic dielectric layers of different sizes are experimentally and theoretically investigated. Thin samples as well samples with transverse sizes comparable with longitudinal ones are used. The measured static magnetic properties of the bulk sample are found to be different from the properties of constituent thin films. This is an evidence for strong interactions between the magnetic layers in the sample, which interact at distances exceeding greatly the distance between adjacent magnetic layers. A theoretic model is developed taking into account magneto-dipole interactions between iron films in a multi-layer system. The model explains the anomalously high demagnetization field of the sample observed in the measurements.     

FLUCTUATIONS OF FLUX LINES ONTHE SURFACE OF SUPERCONDUCTOR

In this paper, we study the magnetic structure of the half-ring flux line ended on the surface of a superconductor. The elemental modes for these half-ring flux lines are the half-ellipse flux lines ended on and perpendicular to the surface. The statistics of these half-ring flux lines is, in a certain degree, similar to the vortex-antivortex pairs in thin superconducting films. An abrupt change of the thermodynamic properties for this system takes place at a temperature lower than Tc. It is analogous to the KT transition in thin superconducting films in certain sense.     

Ni-Ge nanostructures: Role of the interface and the magnetic properties

The surface morphology and local structure of layers in the Ni-Ge and Ge-Ni-Ge-Ni-Ge films have been investigated. It has been shown that the surface of the films follows the roughnesses of the substrate surface, which have characteristic dimensions of 2–4 nm in height and ～100 nm in plane. It has been found that an interface with the depth ranging from 9 to 18 nm is formed at the boundaries between the Ni and Ge layers. The data obtained have been used to explain the specific features of the magnetic properties of the studied films, such as the asymmetry of hysteresis loops at low temperatures and the difference between the temperature dependences of the magnetization of the samples for two cooling modes: in a magnetic field and without a magnetic field.     

Effects of cooling rate and post-heat treatment on properties of ZnO thin films deposited by sol-gel method

Sol-gel spin-coated ZnO thin films are cooled with different rates after the pre-heat treatment. Atomic force microscopy (AFM), X-ray diffraction (XRD), Raman, and photoluminescence (PL) were carried out to investigate the effects of the cooling rate during pre-heat treatment on structural and optical properties of the ZnO thin films. The ZnO thin films cooled slowly exhibit mountain chain structure while the ones cooled rapidly have smooth surface. The ZnO thin films cooled rapidly have higher c-axis orientation compared to the ones cooled slowly. The narrower and the higher near-band-edge emission (NBE) peaks are observed in the ZnO thin films cooled rapidly.     

FLUCTUATIONS OF FLUX LINES ON THE SURFACE OF SUPERCONDUCTOR

In this paper, we study the magnetic structure of the half-ring flux line ended on the surface of a superconductor. The elemental modes for these half-ring flux lines are the half-ellipse flux lines ended on and perpendicular to the surface. The statistics of these half-ring flux lines is, in a certain degree, similar to the vortex-antivortex pairs in thin superconducting films. An abrupt change of the thermodynamic properties for this system takes place at a temperature lower than T_c. It is analogous to the KT transition in thin superconducting films in certain sense.     

Microwave and static magnetic properties of multi-layered iron-based films

Thin ferromagnetic films with in-plane magnetic anisotropy are promising materials for obtaining high microwave permeability. To produce a bulk massive sample from thin films, multi-layer films made of a number of many thin films may be used. The paper reports on an experimental study of microwave and static magnetic properties of multi-layer iron-based films and composite samples made of these. The multi-layer films under study are deposited onto a mylar substrate by a magnetron-sputtering process performed in Ar atmosphere with controlled N₂ admixture. The sputtered iron layers are alternated with SiO₂ layers. The measured static and microwave magnetic properties of the bulk sample are found to differ from the properties of constituent films. This is an evidence for strong interactions between the magnetic layers in the sample, which interact at distances exceeding greatly the distance between adjacent magnetic layers. A theoretic model is developed to account for magneto-dipole interactions between iron films in a multi-layer system. The model explains the anomalously high demagnetization field of the sample observed in the measurements.     

Magnetic properties of CrSb compounds with zinc-blende and wurtzite structures

The electronic structure and magnetic properties of Cr-Sb compounds with zinc-blende and wurtzite structure have been studied by means of the Korringa-Kohn-Rostoker (KKR) band structure method. The occurrence of a half-metallic behavior has been investigated for the bulk systems as a function of lattice parameter, as well as for thin films deposited on different substrates. In the latter case the influence of the surface and interface on the electronic structure is discussed in addition. To study magnetic order in the bulk and within the films, exchange coupling parameters have been calculated from first principles. They have been used for subsequent Monte Carlo simulations, based on a classical Heisenberg Hamiltonian, to obtain the Curie temperature.     

Magnetic and magneto-optical properties of FeRh thin films

The magnetic and magneto-optical properties of FeRh thin films epitaxially deposited onto MgO(1 0 0) substrates by RF sputter-deposition system have been investigated in conjunction with the structure. An intriguing virgin effect has been found in the M–T curves of the as-deposited FeRh thin films, which is presumably interpreted in term of a change in structural phase when heating. Also, a (negative) maximum peak of Kerr rotation at around 3.8 eV has been observed when FeRh thin films are in ferromagnetic state. The polar Kerr rotation angle is found to increase at temperatures above 100 °C, which corresponds to the antiferromagnet (AF)–ferromagnet (FM) transition of FeRh thin films.