Critical Thickness of (001) Texture Induction in FePt Thin Films on Glass Substrates (original) (raw)
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Thickness dependence of (001) texture evolution in FePt thin films on an amorphous substrate
Thin Solid Films, 2008
Thickness dependency of (001) texture evolution in Fe 54 Pt 46 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 Fe 54 Pt 46 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.
Journal of Applied Physics, 2011
The stress state of FePt thin films deposited at room temperature was controlled within the range from 1.01 GPa compressive to 0.18 GPa tensile before taking rapid thermal annealing (RTA). After the order-disorder transformation triggered by RTA at temperatures (T a ) from 650 to 800 C for 5 min, the tensile-stressed films exhibit significant preferred orientation of (001) of L1 0 structure. However, the compressive-strained ones show isotropic texture. Strong (001) texture with high Lotgering orientation factor of 0.9 is obtained at T a ¼ 800 C, resulting in enhanced perpendicular magnetic anisotropy. The results provide direct evidence of stress-induced (001) texture, which could be significant for future applications.
2013
Perpendicular magnetic recording thin films require proper crystallographic growth to ensure that the magnetic easy-axis is aligned normal to the growth plane. The texture and in situ growth stresses of (001) FePt and Fe x Ni (1−x) Pt thin films on various underlayer combinations are studied. These were correlated with the magnetic properties allowing self consistent direct comparisons of the various parameters to be made. It was found that the (001) texture, L1 0 chemical ordering and perpendicular magnetic alignment was improved with the smaller lattice misfit that accompanied a combination of Pt/Cr multilayered and compositionally graded underlayers on a (001) MgO substrate. A Cr underlayer allowed the Pt film to deposit in a relatively strain-free lattice condition from which the FePt based films could grow in a similar strain-free epitaxial condition. In situ stress measurements confirmed that these underlayers reduced the intrinsic compressive growth stresses to approximately one-fifth the FePt stress value for being directly deposited onto the MgO surface. The incorporation of Ni to the (001) growth of FePt facilitated in-plane and out-of-plane c-variant growth for the L1 0 structure. Finally, a linear compositional gradient Fe x Ni 0.48−x Pt 0.52 (0b x b 0.48) thin film was deposited, which exhibited good [001] orientation and perpendicular magnetic alignment. This has been proposed as a magnetic switching architecture for high density, thermally stable but switchable magnetic media grains using current write head fields.
Journal of Applied Physics, 2008
This paper presents a detailed study of structure, morphology, and magnetic properties in FePt thin films epitaxially grown on MgO(100) at intermediate temperatures (≅380°C). It focuses on the effects obtained by in situ annealing the FePt films after deposition. We have demonstrated that the annealing allows one to complete the ordering, thus obtaining an epitaxial L10-FePt film with large perpendicular anisotropy (up to 3×107erg /cm3) and high perpendicular squareness and remanence ratio (both higher than 0.85). At the same time, we have found a peculiar morphology evolution by increasing the annealing time: the interconnected mazelike grains evolve towards interconnected dotlike grains of reduced size (down to 10nm). Due to the interconnection at the grains basis, the increase in the film perpendicular coercivity with the annealing process is moderate (up to 4.1kOe), leading to an increasing anisotropy/coercivity ratio with the annealing time. As a further step towards the understanding of the properties evolution with annealing, we have investigated the magnetic domain pattern and analyzed the domain-period dependence on the anisotropy constant in comparison with the behavior expected by the Kooy-Enz theory [C. Kooy and U. Enz, Philips Res. Rep. 15, 7 (1960)]. The main magnetic properties and reduced grain size obtained after the in situ annealing are promising to realize perpendicular recording media with reduced bit size, high thermal stability, and suitable switching field.
Journal of Magnetism and Magnetic Materials, 2007
FePt thin films were epitaxially grown by RF sputtering on MgO (1 0 0) substrates at 550 1C, followed by in situ annealing at the same temperature. The in situ annealing was found to improve the magnetic characteristics: i.e., the increase in magnetic squareness up to 0.9 and increase in the ratio between anisotropy and coercivity (e ¼ anisotropy field/coercive field ¼ 35.9 for 115 min annealing). Remarkably, a decrease in grain size was also found to occur by increasing the annealing time. r
Effects of AG on structural and magnetic properties of FePt thin films
2009
With the demand on the areal density of magnetic recording media, L1 0 FePt alloy has attracted much attention because of its high magnetocrystalline anisotropy (7×10 7 erg/cm 3), which allows magnetic grain of ~3 nm to be thermally stable. However, lower ordering temperature, lower magnetic exchange coupling, better control over film texture and read-write process on high-coercivity media are challenges to its application in magnetic recording media. In order to improve structural and magnetic performance, Ag was added into perpendicular FePt thin films by cosputtering and sequential sputtering. The microstructures, magnetic properties and phase miscibility of the FePt-Ag films were investigated. When cosputtered with Ag, FePt grain size and magnetic exchange coupling were reduced with increasing Ag content. A study on alloying of FePt-Ag by anomalous x-ray scattering (AXS) suggested that some Ag atoms resided in the FePt long-range order (LRO). Extended x-ray absorption fine structure (EXAFS) study indicated that most Ag atoms formed a separate phase from FePt. The small fraction of Ag atoms alloyed with FePt tended to replace Fe atoms. The coercivity of FePt films significantly increased when cosputtered with Ag. The coercivity enhancement was associated with the pinning effect of Ag and improvement in L1 0 ordering. While Ag cosputtering changed the FePt thin films from perpendicular texture to longitudinal texture, sequential FePt/Ag/FePt deposition not only maintained the perpendicular texture but also improved the magnetic recording performance. Calculation of anisotropy constant (K u) did not show ordering improvement in the sequential deposition. The improved coercivity was attributed to pinning effect and consequential Abstract vi change in magnetic reversal mechanism. Investigation on the microstructure suggested that a nominal 3-nm Ag did not form a continuous layer structure between the FePt layers when the deposition temperature was 350 °C. Surface segregation of Ag confirmed Ag diffusion due to the low surface energy of Ag. Similar deposition at room temperature
Magnetic Properties of Ultra-Thin FePt Films Grown on Oxidized Si Substrates
Springer Proceedings in Physics, 2013
We report the effects of thickness and post annealing temperature on the structural and temperature dependent magnetic properties of FePt (x = 5-50 nm) thin films deposited at ambient temperature on the oxidized Si substrate with an MgO (y = 5, 10 nm) underlayer. All the as-deposited samples show face centered cubic structure, but transformed into L1 0 ordered structure upon annealing. The formation of L1 0 ordered structure depends strongly on the films thickness and annealing temperature. The coercivity of the FePt films with thickness lower than 20 nm was obtained to be less than 3 kOe, but increases rapidly to above 6 kOe for more thicker films. Room temperature magnetic properties and high temperature magnetic properties of the FePt films were studied by analyzing the magnetization data as a function of temperature to understand the stability of the L1 0 ordered structure. High temperature coercivity variation exhibits a linear variation of coercivity up to 540 K and transforms into soft magnetic phase above 640 K. The obtained results are discussed in correlation with the improvement in the L1 0 ordering with annealing and the reduction in the temperature dependence of magnetocrystalline anisotropy energy.
Improvement of Magnetic Properties and Texture of FePt Thin Films on MgO Substrates by Sn Addition
Journal of Magnetics, 2009
In this work, we studied the effects of Sn addition on the ordering temperature of FePt thin film. The coercivity of FePtSn film was about 1000 Oe greater than the coercivity of FePt film for an annealing temperature of 600 o C. Therefore, Sn addition was effective in promoting the L1 0 ordering and in reducing the ordering temperature of the FePt film. From our X-ray diffraction results, we found that in the as-deposited film, the addition of Sn induced a lattice expansion in disordered FePt thin films. After the annealing process, the excess Sn diffuses out from the ordered FePt thin film because of the difference in the solid solubility of Sn between the disordered and ordered phases. The existence of precipitates of Sn from the FePt lattice was deduced by Curie temperature measurements of the FePt and FePtSn films. Therefore, the key role played by the addition of Sn to the FePt film can be explained by a reduction in the activation energy for the L1 0 order-disorder transformation of FePt which originates from the high internal stress in the disordered phase induced by the supersaturated Sn atoms.