退火温度对SmCo永磁薄膜微结构及磁性能的影响

采用直流磁控溅射法制备SmCo薄膜,研究了退火温度对薄膜微结构及磁性能的影响。XRD分析结果表明,当退火温度为600℃时,SmCo5相析出,而Sm2Co17相在700℃析出。SEM照片可看出,退火温度高于900℃时,六方柱状的SmCo5相和菱方状的Sm2Co17相全部析出。随着退火温度的升高,晶粒尺寸增大,当温度达940℃时,晶粒尺寸减小,而在980℃时,晶粒尺寸又将增大。VSM测试表明,与制备态的薄膜相比,退火后的薄膜在垂直于膜面方向的矫顽力、剩余磁化强度及最大磁能积都增大。960℃时得到矫顽力和剩余磁化强度的最大值,800℃时得到最大磁能积的最大值。     

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.     

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.     

Effect of capped layer on microstructure and magnetic properties of FePt films

Sputter-deposited FePt films exhibit an in-plane magnetic anisotropy when MgO is used as the capped layer. The perpendicular magnetic anisotropy of FePt films can be enhanced by introducing a Ag capped layer instead of a MgO capped layer. Although the in-plane coercivity (Hc_//) of FePt films decreases slightly after introducing a Ag capped layer instead of a MgO capped layer, the perpendicular coercivity (Hc_⊥) is increased significantly from 3169 Oe to 6726 Oe. Auger electron spectroscopy analysis confirms that Ag atoms diffuse from the capped layer into the FePt magnetic layer and are mainly distributed at the grain boundary of FePt. This phenomenon results in enhancement of the grain boundary energy and inhibition of grain growth, thus increasing the perpendicular coercivity and reducing the grain size of the FePt film.     

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。     

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.     

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.     

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.     

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.     

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.     

退火温度对方形FePt纳米颗粒磁性及微结构影响

利用高温液相直接合成出了尺寸为7nm具有立方形状的FePt纳米颗粒，研究了样品在不同温度退火后的磁性和微结构．X射线衍射结果表明，当样品经500℃退火1h后，样品开始由无序的fcc结构转变为有序的fct结构．随着退火温度的上升，样品的有序度S和矫顽力也逐渐增大，当退火温度为570℃时，样品的有序度就达到了0.88，7nmFePt颗粒的有序化温度明显低于3～4nmFePt颗粒．     

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.     

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.     

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.     

Effects of the heat treatment on the microstructures and magnetic properties in Alnico 5

In Alnico 5, cooling rate c in a magnetic field from 900°C to 600°C and optimum aging time t at 600°C have the relation of log(t) = 0.417 log (c) + 0.884. However the final magnetic properties are highly dependent on the cooling rate. Spinodally decomposed structures of this alloy show that the faster the cooling rate the smaller the size of the FeCo-rich precipitates and the larger the aspect ratio without change of the volume fraction of the precipitates. The length of the long axis of the FeCo-rich precipitates at a given cooling rate is not uniform due to the interconnection of the subsequent precipitates by the magnetic field effect, and this tendency seems to be stronger when the cooling rate is slower. However the length of the short axis of the precipitates is almost the same at a given cooling rate. The length of the short axis l and the cooling rate c in a magnetic field have the relation oflog (l) = 2.385 - 0.317 log (c). Optimum solution treatment temperature of the low-temperature treatment method was 860°C. This method has higher coercive force than that of the high-temperature treatment method. The FeCo-rich precipitates of the specimen were aligned more parallel to the applied magnetic field with little interconnection of the precipitates and have a higher aspect ratio than that of the high temperature treatment specimen.     

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.     

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。     

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 microstructures and magnetic properties for CoPt/Ag nanocomposite thin films

Ag underlayer (30 nm) has improved the degree of ordering and perpendicular magnetic anisotropy of CoPt films (7.5-10 nm). After annealing at 600 °C and 700 °C, the perpendicular coercivity of CoPt/Ag films has been raised as the thicknesses of CoPt layers are increased. The magnetic easy axis of CoPt/Ag films would change from a random orientation to an out-of-plane orientation. It is found that Ag underlayer with thickness of 30 nm can improve the perpendicular magnetic properties of CoPt layers with thicknesses in the range of 7.5-10 nm. The CoPt/Ag films would be a candidate for perpendicular magnetic recording media.