FeTaC magnetic soft underlayer for L1(0) FePt based perpendicular recording media

FeTaC magnetic soft underlayer under elevated temperature process conditions for L1(0) FePt based perpendicular recording media has been investigated. After annealing FeTaC for 40 min at 350 degrees C, saturation moment increases to 750 emu/cm3 and, coercivity and remanent moment reduce to 2.3 Oe and 166 emu/cm3 respectively. The microstructure of FeTaC annealed at 350 degrees C for 40 min composes of Fe nanocrystals with random orientations immersed in an amorphous matrix. FeTaC surface roughness due to elevated temperature process is reduced by 100 W RF plasma etching and CrRu with (200) orientation is developed. It is found that changing elemental composition due to C diffusion into the CrRu layer and RF preferential etching over Fe, Ta and C has the influence on the magnetic properties of FeTaC.     

Preparation and Magnetic Properties of FePt Nanodot Arrays Sputtering on AAO Templates

FePt nanodot arrays are the promising recording media for future super-high density magnetic recording because of their huge uniaxial magneto-crystalline anisotropy and good signal noise ratio. In this article, FePt nanodot arrays were successfully prepared on anodic aluminum oxide (AAO) templates by magnetron sputtering, and an Ag underlayer was proposed to improve the magnetic properties of FePt nanodot arrays. The dependences of Ag underlayer, annealing temperature, and pore diameter on the magnetic properties of FePt nanodot arrays were investigated. Using the AAO templates with pore diameter of 80 nm and annealing temperature of 600°C, the coercivity of Ag/FePt nanodot arrays is improved significantly to 10262 Oe.     

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.     

Correlation of Magnetic Properties of Co/Cr Bilayer Thin Films with Grain Boundary Diffusion

The microstructure and magnetic properties of Co/Cr bilayer films were examined before and after postdeposition annealing by using transmission electron microscopy (TEM), X-ray diffraction (XRD) technique and vibrating sample magnetometer (VSM). A model of grain boundary (GB) Cr-rich phase growth involving GB diffusion derived from the Cr underlayer was proposed to elucidate the kinetics of the paramagnetic Crrich phase growth along Co GBs within the Co layer. The correlation of the GB Cr-rich phase formati...     

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.     

Low temperature ordering of FePt films by in-situ heating deposition plus post deposition annealing

FePt thin films with 40 nm thickness were prepared on thermally oxidized Si (001) substrates by dc magnetron sputtering at the nominal growth temperature 375 °C. The effects of annealing on microstructure and magnetic properties of FePt thin films were investigated. The as-deposited FePt thin films show soft magnetic properties. After the as-deposited FePt thin films were annealed at various temperatures and furnace cooled, it is found that the ordering temperature of L1₀ FePt phase could be reduced to 350 °C. For FePt thin films annealed at 350 °C, the in-plane and out-of-plane coercivities of the films increased to 510 and 543 kA/m, respectively, and the films had hard magnetic properties. A highly (001) orientation was obtained, when FePt thin films were annealed at 600 °C. And the hysteresis loops of FePt thin films annealed at 600 °C show out-of-plane magnetic anisotropy.     

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.     

The L12 CrPt3 underlayer effect on the ordering of L10 FePt films

This study discusses the effects of a CrPt₃ alloy underlayer on the magnetic properties and microstructure of FePt films. The L1₂ CrPt₃ phase was chemical long-range ordered at a temperature above 600 °C, and the 120-nm thick CrPt₃ film annealed at 800 °C, resulting in ferrimagnetic behavior. The long-range ordered CrPt₃ underlayer slightly increased the ordering of the L1₀ FePt film, as evidenced by the individual L1₂ CrPt₃ and L1₀ FePt (0 0 1) superlattice peaks. An X-ray slow scan of the [FePt/CrPt₃(T °C)]_400°C bilayer shows that the integrated intensity of the L1₀ FePt (0 0 1) peaks was higher on the long-range order L1₂-type CrPt₃ (T = 600, 800) underlayer and lower on the partial short-range order L1₂ and A₁-types CrPt₃ (T = 400) underlayer. However, optimal magnetic properties were obtained in the [FePt/CrPt₃(400 °C)]_400°C bilayer. When a FePt film is deposited on a ferrimagnetic CrPt₃(800 °C) underlayer, the resulting bilayer shows isotropic magnetic hysteresis loops and cannot be saturated at 1.8 T. Atomic force microscopy (AFM) and transition electron microscopy (TEM) show that the L1₂ CrPt₃(800 °C) underlayer exhibits coarse surface roughness and plate-like grains, respectively. From TEM images, all the FePt grains were isolated uniformly by CrPt₃ matrix.     

Magnetic and Morphological Properties of Electrodeposited Thick FePt Films on Metallic (Au, Ag, Cu) Underlayers

Electrodeposited thick films of FePt (with the nominal composition 50 % Fe/50 % Pt) on three metallic (Au, Ag, Au) underlayers were annealed at various temperatures. The magnetic and morphological properties of the resulting films were then monitored. The Au and Ag underlayers promoted the growth of the (bct) L1₀ FePt phase. The greater growth of this phase in the films deposited on the Ag underlayer led to the crystallographic texturing in the (001) direction. This was accompanied by a significant magnetic anisotropy and a negative shift of the remanent magnetization in the presence of an applied field. The coercivity of the Ag underlayer films increased to 18 kOe while the coercivity of the Au underlayer films decreased to ～2 kOe when the annealing temperature was increased to 800 ^°C.     

纳米级FePt/Fe多层膜中微结构的优化与耦合效应

本文用磁控溅射法制备了一系列不同厚度Fe层的FePt/Fe多层膜,经过热处理后成功地制备出具有fct结构的FePt有序相和exchange-spring型永磁体.研究了不同热处理条件下多种膜层厚度与FePt/Fe多层膜结构、磁性及其内在关系,并探讨了FePt/Fe多层膜铁中的磁耦合失效问题.观察了不同热处理条件和层厚的FePt/Fe多层膜的结构变化过程,包括结构相变、有序度和晶粒度.研究了其磁性能随结构变化的规律,发现了耦合失效的模式.     

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.     

Magnetic properties and microstructures of sputtered epitaxial Co-rich Co-Pt films

Co₃Pt films of various thicknesses were deposited on Pt underlayers by conventional sputtering in order to investigate the effects of Pt underlayers and annealing temperatures on their microstructure and the magnetic properties. XRD and HRTEM analyses reveal perpendicular magnetic anisotropy in films of good epitaxial growth of Co₃Pt (002) on the Pt (111) underlayer when annealed at 300 °C. However, Pt atoms in the Pt underlayer will diffuse seriously into the Co₃Pt layer when the annealing temperature is increased to 375 °C. This changes the compositions to approach equiatomic CoPt, and shows in-plane magnetic anisotropy with soft magnetic properties.     

Effect of short annealing times on the magnetoelectronic properties of Co/Pd-based pseudo-spin-valves

We investigated the effects of short annealing times on the magnetoelectronic properties of pseudo-spin-valves (PSV) with perpendicular magnetic anisotropy based on Co/Pd multilayers using a contact hot plate. In order to study the time scale at which the degradation of film properties occurs for possible application in perpendicular MgO-based magnetic tunnel junctions (MTJ), the results were compared against our previous study of Co/Pd PSV based on vacuum annealing. With contact annealing for up to 90 s, no significant changes to the current-in-plane giant magnetoresistance (CIP-GMR), interlayer coupling, sheet resistance and layer coercivities were observed for up to 200 degrees C. At 350 degrees C, a 39 to 46% decrease in CIP-GMR was observed for annealing times of 30 to 90 s, respectively, slightly lower than that observed for vacuum annealing at 230 degrees C for 1 h. Similar results were also obtained for interlayer coupling, sheet resistance and layer coercivities, indicating that short annealing times allow for reduced interlayer diffusion at higher temperatures. However, it is clear that significant degradation of GMR performance occurs at 350 degrees C and above even for annealing times as short as 30 s, indicating the potential difficulty of realizing Co/Pd-based perpendicular MgO-MTJ.     

Microstructure and magnetic properties of (0 0 1)-oriented L10 FePt films: Role of Ag underlayer and Fe/Pt ratio

FePt multilayer films were deposited on Si(1 0 0) substrate with thermally grown SiO₂ film and sputtered Ag underlayer at room temperature by dc magnetron sputtering and subsequently annealing in vacuum. Experimental results suggest that proper thickness of Ag underlayer and slightly rich of Fe content can effectively induce the (0 0 1) texture of FePt films. A Fe_57.4Pt_42.6 thin film on the 8 nm Ag underlayer exhibits a large perpendicular coercivity of 7.6 kOe with magnetic remanence close to 1.     

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.     

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.     

Reduction of ordering temperature of self-assembled FePt nanoparticles by addition of Au and Ag

The [FePt]94Au6 and [FePt]90Ag10 nanoparticle arrays were synthesized on Si substrates by a reverse micellar method, combined with plasma treatment and in-situ deposition of a SiO2 overlayer, and the post annealing step was performed to drive the face-centered cubic to tetragonal phase transition. These FePt nanoparticles exhibit a quasi-hexagonal order with tailored inter-particle spacing and particle size. The effects of the Ag and Au on the structural and magnetic properties of FePt were investigated. The results indicate that both Au and Ag additives can remarkably enhance the coercivity and reduce the ordering temperature, however, the optimum composition is different for them. The optimum composition is determined to be [FePt]94Au6 and [FePt]90Ag10, respectively, for which the ordering temperature of FePt nanoparticles is reduced by -100 degrees C. After 600 degrees C annealing, the [FePt]94Au6 and [FePt]90Ag10 nanoparticles are totally ferromagnetic with apparent larger coercivities of -7.0 kOe, which is about 3.8 kOe larger than that of the pure FePt nanoparticles. The mechanism of the chemical ordering acceleration may be attributed to the defects and strains caused by the Au/Ag additives.     

Lattice Expansion by Adding Oxygen to Control Crystallographic Orientations in Chemically Ordered L10 FePt Films

We fabricated L1₀ FePt thin films by sputtering in reactive oxygen on polycrystalline glass substrates, and we investigated the magnetic properties and crystallographic orientations of the films. Oxygen addition during the FePt deposition promoted heteoroepitaxial growth by decreasing the lattice misfit with the Ag underlayer. In an oxygen/argon ratio of 1.5-3.0 vol.%, the in-plane lattice parameter of the FePt films expanded, and the lattice misfit with the Ag underlayer decreased from 6.3 to 3.9% in the as-deposited state, as determined by grazing incidence X-ray diffraction (GIXRD). Annealing at 700degC for 1 min produced a heteroepitaxially grown L1₀ (001) texture with a large out-of-plane coercivity of 8.8 kOe and a nucleation field of kOe. Transmission electron microscopy showed that average grain size in the as-deposited films was about 4-5 nm and was in the range of 10-15 nm in the annealed films, indicating that there was some grain growth.     

High Coercive NdFeB Thin Film Obtained by Diffusion Annealing

1. IntroductionSince the discovery of the high performance NdFeB permanent magnetll'2] ) there has been much interest in the magnetic properties and its applications.In most of the applications, bulk NdFeB magnetsare used. Due to the dependence of magnetic properties on ndcrostructure, the systematical change ofthe length scales and illtergranular phase, such asin thin films, have been illterested to optimize theirmagnetic properties. The film magnets are made bysputteringl3], MBEI4] and l…     

Sintering Effect of Annealed FePt Nanocrystal Films Observed by Magnetic Force Microscopy

Chemically synthesized FePt nanocrystals can exhibit room temperature ferromagnetism after being annealed at temperatures above 500degC. In thick films composed of FePt nanocrystals, the coercivity can be quite large. However, the coercivity of thin films has been found to decrease significantly with decreasing thickness, to the point that ferromagnetism at room temperature is lost. We studied 12 to 55 nm thick films by using magnetic force microscopy (MFM) under external applied fields. We made smooth films by spin casting 4-nm-diameter FePt nanocrystals and annealing them at 605degC-630degC. Thin FePt films showed lower coercivity than thick films. To help interpret the MFM images, we obtained complementary magnetic and structural data by superconducting quantum interference device (SQUID) magnetometry, transmission electron microscopy (TEM), and X-ray diffraction. We conclude that the magnetic properties of these films are strongly affected by nanocrystal aggregation that occurs during annealing