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.     

Iron-platinum-coated carbon nanocone probes on tipless cantilevers for high resolution magnetic force imaging

High coercivity iron-platinum-coated carbon nanocones (CNCs) have been fabricated for magnetic force microscopy (MFM) by direct-current plasma-enhanced chemical vapor deposition growth of nanocones on tipless cantilevers followed by sputtering and annealing of the FePt film. The FePt-coated CNC probe has many localized magnetic stray fields due to the high-aspect-ratio geometry and small radius of the tip. The MFM imaging on magnetic recording media was performed using CNC probes and compared with the imaging by FePt-coated silicon probes. An image with 20?nm lateral resolution has been demonstrated.     

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.     

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.     

Structure and magnetic property of the FePt/CrPt bilayer

In this work we have studied the growth sequence of L10-CrPt antiferromagnetic layer effects on the microstructure and magnetic properties of the FePt/CrPt bilayer. The microstructure characteristics were investigated by means of X-ray diffraction and the magnetic properties were measured at room temperature by using a vibrating sample magnetometer. Structural analysis showed that the low-temperature ordering and the in-plane orientation of the FePt layer with the CrPt underlayer were promoted due to lattice mismatch optimized after annealing at 350 degrees. Meanwhile, magnetic analysis also revealed that the FePt/CrPt bilayer had much larger exchange bias (H(E)) and higher coercivity (Hc) when the CrPt layer was as the underlayer after annealing at 350 degrees.     

Magnetic Properties of Percolated Perpendicular FePt–MgO Films

Percolated perpendicular FePt-MgO films with a (Fe₄₈ Pt ₅₂)_100-x-(MgO)_x/Pt(001)/Cr(002) structure were prepared by conventional dc magnetron sputtering (x=0-6.13). Magnetic measurements demonstrate that the coercivity of the magnetic film drastically increases from 169 to 285 kA/m as the MgO content is increased from 0 to 0.15 vol.%. However, the grain sizes of the FePt phase do not significantly varying upon doping with MgO. MgO does not appear at the grain boundaries of the FePt phase, but is present as crystalline dots that are uniformly precipitated in the FePt matrix. The MFM images revealed that the domain structure transformed from extending to isolate when the MgO dots precipitated into the FePt grains. Consequently, the MgO dots serve as pinning sites of the domain wall and enhance perpendicular coercivity. Percolated perpendicular magnetic recording is thus regarded as a solution to the problem of thermal instability in ultrasmall grains     

Magnetic properties and microstructure of FePt–SiO2 nanocomposite films fabricated by nanocluster beam technology

Nanocluster beam technology combined with conventional sputtering was used to fabricate FePt–SiO₂ nanocomposite films in this present work. The post-deposition annealing affected the final particle size and size distribution of FePt nanoclusters. The effects of both volume fraction of SiO₂ matrix and annealing temperature on magnetic and microstructural properties were studied. Partial ordering, grain growth and agglomeration of FePt particles in FePt–SiO₂ nanocomposite films occurred during annealing. A higher volume fraction of SiO₂ matrix was effective in suppressing diffusion of atoms and magnetic exchange coupling of FePt grains. Excessive SiO₂ however resulted in a lower degree of FePt ordering and thus lower coercivity.     

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 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.     

退火温度对NiZn铁氧体薄膜性能的影响

采用射频磁控溅射法在Si(100)基片上制备了NiZn铁氧体薄膜,研究了退火温度对薄膜性能的影响.采用XRD分析仪分析了薄膜的相结构,原子力显微镜分析了薄膜的表面形貌,振动样品磁强计测量了薄膜的磁性能,结果表明,随着退火温度的升高,薄膜的结晶状态越好,晶粒尺寸越大,饱和磁感应强度越高,面内矫顽力越小.     

Influences of Sputtering Angles and Annealing Temperatures on the Magnetic and Magnetostrictive Performances of TbFe Films

To increase the low-field magnetostriction of TbFe films, the influences of sputtering angles and annealing temperatures on its magnetic and magnetostrictive performances were systematically investigated. With the change in sputtering angles from 90°to 15°, the in-plane magnetization of TbFe films, at 1600 kA·m-1 external field, is strongly increased. An enhancement in the in-plane magnetostrictive coefficient of the films at 40 kA·m-1 is also observed. A detection of magnetic domains by MFM (magnetic force microscopy) indicates that the easy magnetization direction shifts gradually from perpendicular to parallel to the film plane with decreasing sputtering angles. Annealing can enhance the magnetization and magnetostriction of the TbFe films. However, at too high annealing temperature, both the magnetization and magnetostriction of the TbFe films were suppressed to some extent.     

Impact of Nitrogen Pressure on the Structural, Morphologic and Magnetic Properties of the GaMnN Thin Films

GaMnN thin films were fabricated by using pulsed laser deposition followed by annealing. In our experiments, the impact of the background nitrogen pressure on the crystal quality, morphology and the ferromagnetism of the GaMnN thin films were studied systematically. It is found that the samples deposited at 0.75 Pa have the best crystal quality. All the annealed samples showed ferromagnetic behavior, and the Curie temperature was estimated up to 340 K. We found the magnetization of our samples changes depending on the concentration of Mn³⁺ ions, and the origin of the room temperature ferromagnetism of our samples can be explained by bound magnetic polaron theory. The nitrogen vacancies may cause the ferromagnetism to be weakened.     

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.     

The Role of Ligands in the Synthesis of FePt Nanoparticles

The monosize formation, the ability of self-assembly, and high coercivity after annealing are the properties that lead to the priority of FePt magnetic nanoparticles for the application in recording media. These nanoparticles were synthesized by the superhydride method. The effect of oleic acid and oleylamin ligands on the fabrication of nanocrystals and the stability of the FePt system has been studied. TEM, EDS, XRD, and spectrophotometer analysis show the formation of FePt nanoparticles dispersion in hexane and indicate that oleylamine increases the number of particles in the nucleation stage and decreases the size of the Pt core, whereas the oleic acid controls the shell of the particle and its growth, and, furthermore, causes the stability of the FePt colloidal systems.     

Structure and magnetic properties of sputtered FePtM (M = Ti,Nb) thin films

FePt thin films doped with various Ti and Nb concentrations ranging from 2.9 to 9.1 at.% were prepared by r.f. magnetron sputtering. The structural and magnetic properties of Ti- and Nb-doped FePt thin films were investigated. Structural studies revealed that the long range ordering in FePt thin films depends on the doping concentration and annealing temperature of FePt thin films. The addition of Ti and Nb is found to enhance the grain refining in FePt thin films. The effects of doping concentration on the magnetic properties of FePt thin films were studied and discussed.     

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.     

High coercivity of ordered macroporous FePt films synthesized via colloidal templates

The preparation of a three-dimensionally (3D) ordered macroporous iron-platinum (FePt) film derived from monodisperse FePt nanoparticles (approximately 3 nm in diameter) and polystyrene latex particles (254 nm in diameter) is described. The prepared film has a hexagonally ordered porous structure and coercivity up to 10 kOe after annealing at a temperature of 600 degrees C. We also found that size of FePt particles was maintained at around 3 nm, even after annealing at a temperature of 600 degrees C.     

Effects of Magnetic Annealing on Structure and Magnetic Properties of L10-FePt/Ag Films

The structural and magnetic properties of L1₀-FePt/Ag films were studied by X-ray diffraction and a vibrating sample magnetometer. The FeAg/Pt films were obtained by depositing FeAg thin films on thermally oxidized Si (001) substrates via magnetron sputtering and Pt layers on their surface after annealing FeAg thin films at 400 °C with and without an out-of-plane magnetic field of 10 kOe. These films were further annealed at various temperatures to obtain L1₀-FePt phase. The results indicated that the pre-annealing of FeAg thin films under 10 kOe magnetic field caused (001) orientation of Fe particles, and the deposition of Pt layer on such orientated underlayers reduced the ordering temperature of FePt in FeAg/Pt films, realizing the L1₀-FePt phase at 400 °C. The higher coercivity and ordering degree were also observed in the samples, compared with those pre-annealed without magnetic field at the same annealing condition.     

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.     

Aging effect on coercivity of iron oxide thin films

Changes in magnetic properties for Fe_3-x□_x O₄ (x: oxidation degree) thin films made by reactive sputtering and subsequent heat treatments have been examined under room temperature aging and constant temperature annealing. Aging causes variations in coercivity of insufficiently oxidized films which have a specific resistance of less than 1×10¹ Ω·cm, while the coercivity of γ-Fe₂O₃ (x=1/3) did not change. This phenomenon did not depend on additive elements or preparation method. Other magnetic properties such as saturation magnetization, residual magnetization, squareness ratio and coercive squareness, were not affected by aging for any Fe_3-x □_xO₄ composition. The activation energy for a coercivity change is 0.72-0.95 eV near room temperature for films with a specific resistance below 1×10¹ Ω·cm. It was confirmed that only the coercivity varied at 20°C, while both coercivity and the degree of oxidation changed with annealing at 100°C