Effect of carbon additive on microstructure evolution and magnetic properties of epitaxial FePt (001) thin films

FePt:C thin films were deposited on CrRu underlayers by DC magnetron co-sputtering. The effects of C content, FePt:C film thickness and substrate temperature on the microstructural and magnetic properties of the epitaxial FePt (001) films were studied. Experimental results showed that even with 30 vol.% C doping, the FePt films could keep a (001) preferred orientation at 350 °C. When a FePt:C film was very thin (< 5 nm), the film had a continuous microstructure instead of a granual structure with C diffused onto the film surface. With further increased film thickness, the film started to nucleate and formed a column microstructure over continuous FePt films. A strong exchange coupling in the FePt:C films was believed to be due to the presence of a thin continuous FePt layer attributed to the carbon diffusion during the initial stage of the FePt:C film growth. Despite the presence of a strong exchange coupling in the FePt:C (20 vol.% C) film, the SNR ratio of the FePt:C media was about 10 dB better than that of the pure FePt media. The epitaxial growth of the FePt:C films on the Pt layers was observed from high resolution TEM cross sectional images even for the films grown at about 200 °C. The TEM images did not show an obvious change in the morphology of the FePt:C films deposited at different temperatures (from 200 °C to 350 °C), though the ordering degree and coercivity of the films increased with increased substrate temperature.     

Thickness dependence of (001) texture evolution in FePt thin films on an amorphous substrate

Thickness dependency of (001) texture evolution in Fe₅₄Pt₄₆ thin films on an amorphous substrate was investigated using in-house X-ray diffraction or a synchrotron source. The (001) texture was well developed in Fe₅₄Pt₄₆ thin films, especially when its thickness was equivalent to the grain height. The findings show that strain relaxation anisotropy along the film axis, which leads to a (001) crystal (a crystal with a (001) plane parallel to the film plane) that is more stable than others, was large for a low thickness film. In addition, abnormal grain growth was used to explain the abrupt development of a (001) texture. The advantage of multilayered as-deposited structure is also discussed.     

Ag衬底层对FePt薄膜结构和性能的影响

采用磁控溅射方法在自然氧化的单晶Si(100)衬底上制备了双层结构的FePt-X/Ag(X=Ag或Pt)薄膜.以20nm厚的Ag做衬底,可以制备出易磁化轴垂直基片的FePt合金薄膜;Ag在FePt薄膜中优先团聚,不利于控制FePt晶粒的长大,调整Pt的含量可以控制热处理过程中FePt薄膜的晶粒尺度;通过XRD、TEM、VSM对薄膜样品的结构、晶粒尺寸的观察和磁性检测,我们认为FePt合金薄膜有序化转变的最佳热处理温度在400℃;经过500℃热处理,薄膜软硬磁耦合较好,晶粒尺寸约为100nm,有最大的矫顽力1.04×106A/m.     

Electronic and magnetic properties of ultra-thin epitaxial magnetite films on MgO(001)

The electronic and magnetic properties of epitaxial Fe₃O₄ (001) films on MgO(100) substrates were studied throughout the 2.5- to 30-nm thickness range using conversion electron Mössbauer spectroscopy. Despite the superparamagnetism that was observed for film thickness below 5 nm, the Verwey transition persisted even for the thinnest film. Temperature-dependent Mössbauer measurements between 80 K and 400 K revealed that the activation energy for the magnetic moment fluctuations in the 3-nm magnetite film is higher than the magnetic anisotropy energy by an order of magnitude.     

High-density perpendicular magnetic recording media of granular-type (FePt/MgO)/soft underlayer

Perpendicular magnetic recording media, composed of granular-type FePt-MgO films on Fe-Ta-C soft magnetic underlayer (SUL), have been fabricated on to 2.5-in glass disks. [001] textured FePt granular films with high-perpendicular magnetic anisotropy were obtained by annealing the FePt/MgO multilayer films. The FePt grain size, perpendicular coercivity, magnetic activation volume, and the exchange coupling between the FePt grains were found to be strongly dependent on the initial multilayer structures and the annealing conditions. The recording performance of the disks was evaluated by a spin-stand. The obtained results reveal a close correlation between the recording performance and magnetic properties. The thermal stability of the granular-type FePt media was studied using high-temperature magnetic force microscopy (MFM) technique, equipped with in situ sample heating, in the temperature range 25/spl deg/C-200/spl deg/C. The estimated signal decay at high temperature is ascribed to the temperature dependent magnetic anisotropy behavior.     

Ag底层对TbFeCo薄膜磁性能的影响

采用射频磁控溅射法在玻璃基片上制备了TbFeCo/Ag非晶垂直磁化膜，研究了Ag底层厚度对TbFeCo薄膜磁性能的影响。原子力显微镜、振动样品磁强计与磁光盘测试仪测量结果表明：薄的银底层具有较高的表面粗糙度可以显著增大TbFeCo薄膜的矫顽力，改善TbFeCo薄膜的磁光温度特性，该薄膜有望用作高密度垂直记录介质与光磁混合记录介质。     

溅射工艺及底层对SmCo薄膜磁性能的影响

用多靶射频磁控溅射系统在玻璃基片上制备了SmCo磁性薄膜。并采用控制变量法研究了溅射功率、溅射时间以及溅射气压等工艺参数对薄膜磁性能的影响。结果发现，当磁性层溅射功率为60W,溅射气压为0.5Pa，溅射时间为8min；底层溅射功率为125W，溅射气压为0．5Pa，溅射时间为4min时，薄膜的矫顽力高达2．79×10^5。底层对SmCo薄膜的磁性能也有影响，振动样品磁强计测量结果表明：相比Cr、Ti底层，以Cu作为底层所得到的SmCo薄膜磁性能更好，薄膜矫顽力分别比用Cr、Ti作底层时高出56％，40％。     

FePt单层连续膜和颗粒膜的制备与磁性能研究

利用磁控溅射在不同Ar气压下制备了不同膜厚的FePt薄膜。利用透射电镜(TEM)研究了溅射气压和膜厚对薄膜形貌的影响,利用振动样品磁强计(VSM)研究了溅射气压和膜厚对薄膜磁性能的影响。结果表明溅射气压和膜厚对溅射态单层FePt薄膜的表面形貌、颗粒尺寸有很大影响。随着溅射气压的增大,颗粒尺寸减小,从连续膜转变成颗粒膜;随着膜厚的增加,颗粒尺寸变大,从颗粒膜变成连续膜。通过调节溅射气压可以控制FePt的岛状结构,从而获得较理想的FePt颗粒薄膜。溅射气压和膜厚对经过热处理的L10-FePt薄膜的磁性能有很大影响。随着溅射气压增加,形核场由正值转变成负值,矩形比有增大趋势;随着厚度的增加,无序-有序相转变更充分。     

Substrate effects on surface morphologies and magnetic properties of nanostructured FePt thin films

The substrate effects on surface morphologies, crystal structures, and magnetic properties of the sputter-deposited FePt thin films on Corning 1737, normal glass, and Si wafer substrates, respectively, were investigated. High in-plane coercivities of 10 kOe were obtained for the air-annealed films on Corning 1737 and Si wafer, where both films similarly have granular-like morphologies. Besides, increasing grain size and surface roughness of all the FePt films with the post-anneal temperature were observed. Moreover, partially separated grains were seen in the film on Si wafer, where the formation of Fe silicides during post-anneal is suspected, in which has enhanced the magnetic ordering.     

Effect of Ag underlayer on microstructures and perpendicular magnetic properties of CoPt nanocomposite thin films

CoPt/Ag films were prepared by magnetron sputtering on glass substrates and subsequent annealing. The dependence of degree of ordering and magnetic properties on Ag film thickness and annealing conditions were investigated. It was found that the Ag underlayer played a dominant role in inducing the (001) texture of the CoPt film after annealing. CoPt films with a thickness about 20 nm and Ag underlayers with a thickness about 70 nm are easy to obtain a large degree of ordering and a perpendicular magnetic anisotropy after annealing at 700 degrees C for 30 min. CoPt/Ag films with out-of-plane coercivity (Hc (perpendicular)) in the range of 13.5-14.0 kOe and a out-of-plane squareness (S(perpendicular)) of 0.97 were obtained after annealing at 700 degrees C for 30 min. Ag underlayer is beneficial to enhance the Hc(perpendicular)and S(perpendicular) of CoPt film significantly. The degree of ordering and perpendicular magnetic properties of the CoPt films which deposited on Ag underlayer are larger than those of the single layer CoPt films.     

溅射方法对FePt:Ag颗粒膜磁性能及微观结构的影响

分别采用共溅射和多层膜溅射方法制备了FePt:Ag颗粒膜.样品的磁性能和微观特性分别用振动样品磁强计(VSM)、磁力显微镜(MFM)和透射电镜(TEM)进行了表征.研究结果表明:多层膜溅射制备的FePt:Ag颗粒膜能在较低的退火温度下发生有序化相变;而共溅射制备的FePt:Ag颗粒膜经过相同的退火条件后,具有更高的矫顽力,及更细、分布更均匀的晶粒和磁畴结构.     

Crystallographic structure and magnetic properties in L1(0) FePt thin films deposited at different temperature

The crystallographic structure and magnetic properties of L1(0) FePt thin films deposited at different substrate temperature were investigated systematically in present paper. The ordered L1(0) FePt thin film was developed when substrate temperature is higher than 300 degrees C. The ordering parameter S, the degree of tetragonality c/a, and the epitaxial quality of the films, increase with increasing substrate temperature. The squareness and coercivity in the direction perpendicular to the film increase as the substrate temperature is increased and the perpendicular anisotropy is developed when the substrate temperature is higher than 300 degrees C. The magnetic anisotropy Ku increases with increasing substrate temperature and it might be concluded that the magnetic anisotropy of ordered L1(0) FePt thin films mainly stems from the magnetocrystalline origin and also possibly due to pair ordering mechanism.     

Structure of ultrathin MgO films on Mo(001)

We have studied the structure of ultrathin MgO films grown on a single crystal Mo(001) surface. Scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) were used to investigate the effect of substrate temperature and oxygen partial pressure on the growth and morphology of these films. LEED indicates the growth of (100) films with MgO 〈110〉 directions oriented along 〈100〉 directions of the substrate. Despite the insulating nature of bulk MgO, films up to 25-Å thick are sufficiently conducting to perform STM measurements. STM reveals Mg deposition in an oxygen ambient at substrate temperatures from 300 to 900 K produces uniform films. Films as thick as eight atomic layers typically have only three layers exposed. These films consist of small domains between 20 and 60 Å in diameter. The domain shapes are random and the perimeters show no preferred orientation. In contrast, films grown at temperatures in excess of 1000 K exhibit larger three-dimensional MgO islands (Volmer-Weber growth). Steps on these high temperature films orient preferentially along thermodynamically favored MgO 〈100〉 directions. STM images of films deposited at high temperature exhibit a checkerboard pattern. The dimensions and symmetry of this pattern are consistent with the coincidence arising from the mismatch of the MgO(100) and Mo(001) lattice. Annealing room temperature deposited films results in island coalescence and produces uniform films with domains in excess of 100 Å. The perimeters of these domains are oriented along MgO 〈100〉 directions.     

Effects of MgO and MgO/Pd seed-layers on perpendicular magnetic anisotropy of CoPd thin films

We studied the effects of MgO and MgO/Pd seed-layers on perpendicular magnetic anisotropy in co-sputtered CoPd films. CoPd films with the MgO seed-layer showed perpendicular magnetic properties that were superior to those with another after annealing. The loop squareness was unity, indicating strong perpendicular magnetic anisotropy, when the MgO seed-layer was thicker than 2 nm. We observed that the out-of-plane CoPd (111) texture was strongly developed, as well as the in-plane tensile stress in the CoPd films. The magnetoelastic anisotropy coming from a negative magnetostriction λ₁₁₁ under the in-plane tensile stress dominating over other anisotropies is likely responsible for creating such strong perpendicular magnetic anisotropy. In the case of the MgO/Pd seed-layer, the CoPd films showed mixed anisotropy having both in-plane and out-of-plane magnetic anisotropy components after annealing. The appearance of the strong (100) texture of the CoPd films with the MgO/Pd seed-layer is believed to have caused the decrease in the perpendicular magnetic anisotropy that originated from the magnetoelastic anisotropy due to the additional contribution from the positive magnetostriction λ₁₀₀ but less contribution from the negative magnetostriction λ₁₁₁ when the CoPd films are under in-plane tensile stress.     

Effects of Os inserted layers on the microstructures and magnetic properties of the FePt films

The microstructure and magnetic properties of multilayer [Os(t)/FePt(x)]n films on a glass substrate with a 10 nm Os buffer layer by ion beam sputtering have been studied as a function of the annealing temperatures between 300 and 800 degrees C. Here, t = 0.2, 1 or 5 nm and x varied from 10, 20, 25, 50, to 100 nm with its associated n value of 10, 5, 4, 2, and 1, respectively. No diffusion evidence was found in samples with a thin Os layer and t > or = 1 nm. The average grain size of the multilayer films can be well controlled by both annealing temperature and thickness of the FePt layer by a very thin Os space layer with t > or = 1 nm. The enhancement of H(c) can be understood from the fact that for a FePt film with an Os spacer layers, the increasing number of Os layer will inhibit the grain growth of FePt grains and enriches the grain boundary. We have experimentally demonstrated that even with a very thin 1 nm Os spacer layers, the [Os(t)/FePt(x)]n multilayer films can exhibit good hard magnetic properties and are attractive candidates for ultrahigh density magnetic recording media.     

Effects of annealing time on the structural and magnetic properties of L10 FePt thin films

Thermal annealing of [Fe 1.65 nm/Pt 1.84 nm]₅₀ multilayers at 673 K for various annealing times between 60 and 12000 s leads to the direct formation of the fully ordered L1₀ FePt phase with (111) texture. The average grain sizes, determined from X-ray diffraction size-strain analysis, are smaller than the critical size for multi-domain FePt particles, suggesting the presence of single-domain (SD) grains. The coercivity increases with annealing time and increasing grain size and reaches values of about 955 kA/m. The remanence values are typical for randomly oriented weakly-interacting particles. A decrease of the remanence with annealing time suggests a decrease of the intergrain exchange interactions with annealing time. Analysis of minor loops and the initial magnetization curves shows the presence of a broad distribution of critical fields, which the individual SD particles have to overcome for the magnetization reversal.     

Giant pyroelectric coefficient of Mn-doped PLT thin films epitaxially grown on (001) Pt/MgO

The c-axis-oriented epitaxial thin films of Mn-doped Pb_1−xLa_xTi_1−x/4O₃ (PLT) on (001) Pt/MgO substrates were prepared by rf-magnetron sputtering. To investigate the effect of the doped ion, 0-1.7 mol% MnO₂ added to the PLT target powder. The temperature dependence of the relative dielectric constant ?_r measurements and modified Curie-Weiss plots suggested that the increasing of diffuseness n was induced by high-La substitution and the diffuseness n of PLT thin films decreased by the addition of Mn, considerably. Inner stress and thermodynamic analysis were carried out and the results propose that the increasing of γ with Mn doping caused by increasing the misfit strain of the c-axis-oriented epitaxial PLT thin films and substrate. As a result, giant pyroelectric coefficient (γ = 15.8 × 10⁻⁸ C/cm² K) of Mn-doped epitaxial PLT thin film was achieved.     

Piezoelectric properties of (K,Na)NbO3 thin films deposited on (001)SrRuO3/Pt/MgO substrates

(K(x),Na(1-x))NbO(3) (KNN) thin films were deposited on (001)SrRuO(3)/(001)Pt/(001)MgO substrates by RF-magnetron sputtering, and their piezoelectric properties were investigated. The x-ray diffraction measurements indicated that the KNN thin films were epitaxially grown with the c-axis orientation in the perovskite tetragonal system. The lattice constant of the c-axis increased with increasing concentrations of potassium. The KNN thin films showed typical ferroelectric behavior; the relative dielectric constant epsilon(r) was 270 to approximately 320. The piezoelectric properties were measured from the tip displacement of the KNN/MgO unimorph cantilevers; the transverse piezoelectric coefficient epsilon*(31) (= d(31)/s(E)(11)) of KNN (x = 0) thin films was calculated to be -0.9 C/m(2). On the other hand, doping of potassium caused an increase in the piezoelectric properties, and the KNN (x = 0.16) films showed a relatively large transverse piezoelectricity of epsilon*(31) = -2.4 C/m(2).     

Electrical properties of electroplated Cu(Ag) thin films

To increase the electromigration resistance of copper interconnects copper alloy systems are of interest. In the present paper electrical properties of Cu(Ag) films will be discussed with respect to heat treatment and in comparison to copper and other alloy systems. The investigations show that the electrical resistivity of Cu(Ag) films is very low in comparison to other copper alloy systems. Up to an alloy content of about 2 at.% Ag the International Technology Roadmap for Semiconductors criterion of 2.2 μΩcm (scattering by geometrical constraints neglected) can be fulfilled after heat treatment. The various components of the electrical resistivity will be discussed in detail. The investigations show that grain growth and the redistribution of silver and impurities dominate the electrical resistivity evolution.     

Effects of copper concentration on the properties of Cu2CoSnS4 thin films co-electrodeposited on the FTO substrate

Journal of Materials Science: Materials in Electronics - The optimization of the factors influencing the co-electrodeposition method makes it extremely efficient in the production of thin films...