Effect of annealing in external magnetic field on the microstructure and magnetic properties of FePt films

We have studied the influence of annealing in an external magnetic field on the microstructure and magnetic properties of a multilayer Si/Fe(2 nm)/Fe₅₀Pt₅₀(20 nm)/Pt(2 nm) structure synthesized by means of sequential RF magnetron sputtering of the components. The magnetic field was oriented perpendicular to layers of the structure. It is established that annealing in the external magnetic field leads to the formation of predominant (001) texture in the multilayer structure with L1₀-FePt phase. Thus, a method of obtaining multilayer structures based on FePt films required for the perpendicular magnetic recording has been developed.     

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.     

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.     

Effect of AlN layer thickness on structure and magnetic properties of FePt/AlN multilayers

FePt (50 nm) and [FePt(xnm)/AlN(1, 2, 3 nm)]₁₀ (x=2, 3 nm) films were prepared by RF magnetron sputtering technique, then were annealed at 550 °C for 30 min. This work investigates the effect of AlN layer thickness on structure and magnetic properties of FePt/AlN multilayers. Superlattice (0 0 1) peaks can be found in the grazing incidence X-ray diffraction of FePt and [FePt (3 nm)/AlN (1, 2, 3 nm)]₁₀ films, which indicate that the FCC phase has been partially transformed into ordered L1₀ phase. Compared with the single layer FePt film, superlattice (0 0 1) peaks of FePt/AlN multilayers are weak and wide, which indicates that the introducing of AlN hinders the growth of FePt particle, and also shows the introducing of AlN is not beneficial to the transformation from FCC phase to L1₀ phase. In addition, the low-angle XRD spectra show the layered structure of FePt/AlN has been broken after annealing. The coercivities, particle size, intergrain exchange interactions of FePt/AlN films are decreased with increasing AlN layer thickness.     

FePtAg颗粒薄膜的制备及性能表征

采用磁控溅射方法在自然氧化的单晶Si(100)基片上制备了FePtAg颗粒薄膜.通过调整靶材的溅射速率、控制掺杂Ag元素的含量,选择适当的热处理工艺,获得了晶粒尺寸约5nm,分布均匀的FePt颗粒薄膜,矫顽力为3.2×105A/m,磁滞回线具有良好的矩形度,薄膜内部无交换耦合作用,适用于高密度磁记录介质材料.     

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.     

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.     

High perpendicular hard magnetic properties of nanocomposite Co-rich Co-Pt/Pt double-layered films by epitaxial deposition without capped layer

The HRTEM cross-sectional lattice image shows that a well epitaxial growth of hcp Co-rich Co-Pt (002) on Pt (111) underlayer leads to good perpendicular magnetic anisotropy of Co-rich Co-Pt film. It is found that both the perpendicular coercivity (Hc_⊥) and perpendicular squareness (S_⊥) of Co-rich Co-Pt films without Pt capped layer are larger than that of Co-rich Co-Pt films with Pt capped layer. The cross-sectional TEM-EDS and AES analysis confirm that the oxygen atoms will diffuse from film surface into the Co-rich Co-Pt film without adding Pt capped layer, and it react with cobalt atoms to form CoO, which is detected by XPS analysis. The increase in perpendicular hard magnetic properties of Co-rich Co-Pt film without Pt capped layer is mainly due to form CoO in the Co-rich Co-Pt film.     

FePt nanocluster films for high-density magnetic recording

High anisotropy L1(0) ordered FePt thin films are considered to have high potential for use as high areal density recording media, beyond 1 Tera bit/in2. In this paper, we review recent results on the synthesis and magnetic properties of L1(0) FePt nanocomposite films. Several fabrication methods have been developed to produce high-anisotropy FePt films: epitaxial and non-epitaxial growth of (001)-oriented FePt:X (X = Au, Ag, Cu, C, etc.) composite films that might be used for perpendicular media; monodispersed FePt nanocluster-assembled films grown with a gas-aggregation technique and having uniform cluster size and narrow size distribution; self-assembled FePt particles prepared with chemical synthesis by reduction/decomposition techniques, etc. The magnetic properties are controllable through variations in the nanocluster properties and nanostructure. FePt and related films show promise for development as heat-assisted magnetic recording media at extremely high areal densities. The self-assembled FePt arrays show potential for approaching the ultimate goal of single-grain-per-bit patterned media.     

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.     

Effects of annealing on the magnetic properties and microstructure of Fe-ZrN nanocomposite films

We have studied the influence of thermal annealing on the magnetic properties and microstructure of 0.7-μm-thick Fe-ZrN nanocomposite films obtained by a reactive RF magnetron sputtering technique on non-conductive substrates. The near-surface and bulk magnetostatic characteristics of the films were studied using magnetooptical and vibrating-sample magnetometers, respectively. The microstructure was determined by X-ray diffraction. It was established that the magnetic characteristics strongly depend on the annealing temperature. These dependences are explained by structural changes induced in the films by the thermal treatment.     

纳米结构FePt薄膜的结构与磁性研究

采用磁控溅射方法在自然氧化的单晶Si（100）衬底上制备了纳米结构的Fe,Pt100-x（X=30at％-60at％）薄膜。高温XRD分析表明,薄膜在500℃热处理有明显的面心立方FCC结构向面心四方FCT结构转变。通过VSM、AFM对薄膜样品的磁性检测和晶粒尺度的观察,FePt合金薄膜有序化转变的最佳热处理温度在400—500℃,在这个热处理温度范围内,薄膜软硬磁耦合较好,矫顽力适当（306kA／m）,晶粒尺寸约为10nm,适合于做高密度磁记录介质材料。     

The effect of thickness on the texture and magnetic properties of single-layered FePt films by rapid thermal annealing

The single-layered FePt films with thickness in the range of 5 to 50 nm are deposited directly on Si(100) substrate without underlayer, then post annealed at 700 degrees C by rapid thermal annealing (RTA) technique. As the film thickness of FePt is over 20 nm, the L1(0) FePt(111) preferred orientation is presented and tended to in-plane magnetic anisotropy. However, the L1(0) FePt(001) texture is obtained and exhibited perpendicular magnetic anisotropy as the film thickness is decreased to 10 nm. Its perpendicular coercivity (Hc(perpendicular)), saturation magnetization (Ms) and perpendicular squareness (S(perpendicular)) are 14.8 kOe, 795 emu/cm3 and 0.79, respectively. On the other hand, both the grain size and domain size of FePt film decrease with decreasing the film thickness of FePt. The grain size for 10-nm FePt film is as small as 9.7 nm with domain size of 123 nm, which reveal its significant potential as perpendicular magnetic recording media for ultra high-density recording.     

CaO对Mn-Zn铁氧体微观结构与磁性能的影响

采用传统氧化物陶瓷工艺制备了CaO-Bi2O3-MoO3-Nb2O5复合掺杂高磁导率Mn-Zn铁氧体材料,利用扫描电子显微镜(SEM)、B-H测试仪和阻抗分析仪等对材料结构和磁性能进行了表征,研究了不同添加量CaO对高磁导率Mn-Zn铁氧体的微观结构和磁性能的影响.结果表明,添加适量的CaO可以细化晶粒、提高材料的频率特性和品质因数Q,降低材料的损耗;当质量分数CaO=0.030%时,材料具有最佳的综合性能:μi=9 772.22,L200/L10=99.36%,室温PCV=435.14mW/cm3.     

Effects of Cu underlayer on the growth and magnetic properties of FePt thin films on MgO (001) substrate

During ordering process of face centered tegragonal (fct) L1(0) phase of the FePt alloy, there exist three growth variants of axes (001) from original disordered fcc structured phase. When FePt film was directly deposited on the MgO (001) substrate, the variant perpendicular to the film plane grew, resulting in a low out-of-plane coercivity of 1.3 kOe. By using Cu underlayer, two variants lying in the film plane got same chance to grow, which caused an in-plane perpendicular alignment of the tetragonal axes of FePt L1(0) phases. The crystallographic relationship between Cu and FePt layers is Cu (100)<100>//fct FePt (100)<100>. A high in-plane coercivity of 4.6 kOe was obtained due to the high density of micro-defects (mcro-twins, anti-phase boundaries, etc.) in the film plane. This work demonstrated a way of selecting the growth variants of ordering process to adjust the magnetic properties of the ordered FePt thin films.     

Film thickness dependence of microstructures and magnetic properties in single-layered FePt films by in-situ annealing

The FePt films with various thicknesses (t) of 5 to 50 nm are deposited on Si(100) substrate without any underlayer by in-situ annealing at substrate temperature (Ts) of 620 °C. A strong (001) texture of L1₀ FePt film is obtained and presents high perpendicular magnetic anisotropy as the film thickness increases to 30 nm. By further increasing the thickness to exceed 30 nm, the (111) orientation of L1₀ FePt is enhanced greatly, indicating that the quality of perpendicular magnetic anisotropy degrades when the thickness of the FePt film is greater than 30 nm. The single-layered FePt film with thickness of 30 nm by in-situ depositing at 620 °C shows good perpendicular magnetic properties (perpendicular coercivity of 1033 kA/m (13 kOe), saturation magnetization of 1.08 webers/m² and perpendicular squareness of 0.91, respectively), which reveal its significant potential for perpendicular magnetic recording media.     

Influence of vanadium concentration on the microstructure and magnetic properties of V-doped ZnO thin films

Vanadium doped ZnO thin films (Zn_1 − xV_xO, where x = 0.05 or x = 0.13) were grown on c-cut sapphire substrates using pulsed laser deposition technique. Their structure and magnetic properties were examined in relation to the doping concentration. All deposited films were highly oriented along the c-axis and exhibited ferromagnetic behavior with a Curie temperature up to 300 K. The crystal structure was found to be better for layers with lower vanadium concentration. The films had a porous fine-grained microstructure and a column-like character as the V concentration was reduced. A weak dependence of magnetization on temperature was observed. The saturation magnetization was found to be strongly dependent on the crystal structure, grain size and V-ion concentration.     

激光重熔对热浸渗铝层组织和性能的影响

热浸渗铝层中通常存在大量的孔洞和裂纹,严重影响渗铝钢的耐蚀性.采用JHM-1GY-400型YAG(晶体)激光器对Q235钢的热浸渗铝层进行激光熔凝处理,借助扫描电镜、电子探针、金相显微镜、X射线衍射仪、显微硬度计等仪器对激光处理前后渗铝层的显微组织、相组成及性能进行了分析.通过测定在3.5%NaCl水溶液中的极化曲线,讨论了激光熔凝处理对渗铝层耐蚀性的影响.结果表明,采用适当的激光处理工艺,可消除渗铝层中的裂纹及孔洞,渗层变得更加致密,从而使其在3.5%NaCl水溶液中的耐蚀性高于未激光处理的渗层.并且其显微组织发生了高铝ξ相(FeAl2)向低铝β2相(FeAl)的转变,导致渗层显微硬度和脆性降低,渗层综合性能得到改善.     

Effect of sintering conditions on microstructure and magnetic properties of Mn-Zn ferrites

Commercial and specially-prepared Mn-Zn ferrites were characterized, in terms of magnetic performance, microstructure and local composition, by various techniques. The results show the relevance of the structure of the interfaces between grains, the importance of uniform grain size and, finally, the role of composition homogeneity throughout the sample and the atmosphere utilized. The practical relevance of these findings is also discussed.