L10 Ordered FePt Thin Films Research Articles

Magnetic properties and structure of Gd-implanted L1 FePt thin films

In this study, we have investigated the effect of Gd implantation on composition, chemical order, and magnetic properties of 20 nm thick L10 ordered FePt thin films. We show that upon Gd implantation at 30 keV even a small amount of 1 at. % is sufficient to destroy the L10 order, resulting in a soft magnetic A1 FePt alloy, with the exception of a thin L10 ordered layer located at the film/substrate interface. Additionally, a strong resputter effect is observed which results in a large decrease in film thickness as well as to a reduction in Fe content in the FePt alloy. Post-annealing of samples in Ar atmosphere did not result in a restoration of the L10 order, but leads to a transformation to pure Pt and Fe2O3, facilitated by the presence of a high density of vacancies induced by the implantation process.

Exploring the potential of remote plasma sputtering for the production of L10 ordered FePt thin films

Lowering the temperature at which the desirable L10 phase forms in FePt thin films is a key requirement in the development of next generation high-density data storage media and spintronic devices. Remote plasma sputtering offers a higher degree of control over the sputtering parameters, allowing the properties of films to be tailored, and potentially can affect the ordering kinetics of the L10 phase of FePt. Here, we report a comprehensive study of FePt thin films deposited under a range of temperatures and sputtering conditions. X-ray diffraction and magnetometry investigations show that whilst FePt thin films ordered in the L10 phase with high perpendicular anisotropy can be produced using this technique, there is no significant reduction in the required ordering temperature compared with films produced using conventional DC sputtering. Optimally ordered L10 FePt films were fabricated when the film was deposited at a substrate temperature of 200 °C, followed by post annealing at 750 °C.

Large enhancement of magnetic moment in L10 ordered FePt thin films by Nd substitutional doping

We studied L10 ordered Fe50Pt50−xNdx alloy films, which showed a large enhancement (~18.4% at room temperature and ~11.7% at 10 K) of magnetic moment with 6 atomic % of Nd. Analysis of the x-ray magnetic circular dichroism spectra at the Fe L3,2 edges and Nd M5,4 edges in Fe50Pt44Nd6 films indicated a significant contribution of the Nd orbital moment. The origin of the large enhancement of magnetic moment was attributed to the effect of ferromagnetic coupling of the total magnetic moments between Fe and Nd. Density functional theory based first principles calculations supported the experimental observations of increasing moment due to Nd substitution of Pt.

Micromagnetic modeling of L10-ordered FePtmagnetic thin films

The L10-ordered FePt films are promising materials for ultra high density magnetic recording media due to their high magnetic anisotropies. In this work, the L10-ordered FePt thin films are prepared by magnetron sputtering on CrW underlayer. A three-dimensional micromagnetic model, based on the symmetry of the L10 phase, is set up for FePt perpendicular media. According to the mismatch between the underlayer and FePt magnetic layer, a residual tensile stress is applied in the film plane. The simulated M-H loops accord well with the experimental results. The tetragonal crystalline anisotropy, especially high in-plane anisotropy, could enlarge the in-plane coercivity. The simulated perpendicular and longitudinal loops each have an open up in the tail, which is mainly due to the magnetostriction of the L10 phase.

Fabrication of highly L1-ordered FePt thin films by low-temperature rapid thermal annealing

Highly L10-ordered FePt thin films with a strong (001) texture were successfully fabricated on amorphous substrates simply by co-sputtering and rapid thermal annealing at a low temperature of 400 °C. The morphology of FePt thin films depended strongly on the heating rate, changing from a continuous structure with an atomically flat surface to an island-like structure. The change of the morphology resulted in a drastic increase of coercivity, indicating that the magnetization process could be controlled by the heating condition. This fabrication method of ordered FePt thin films is favorable in view of the compatibility for a practical device fabrication process.

Study of reorientation processes in L10-ordered FePt thin films

We report on the development of structural and magnetic order in epitaxially grown L10 FePt thin films. Upon annealing, the easy axis of magnetization changes from the out-of-plain into the in-plain direction. We found that the overall fraction of reoriented domains first increases but after certain time decreases before achieving a saturated state. The results are based on conversion electron Mössbauer spectroscopy studies and confirm Monte Carlo simulations in nano-layered FePt. We present a modified version of the Johnson–Mehl–Avrami (JMA) model adequately describing the experimental findings. Two dynamical processes, the first being a 2D-growth, dominate the initial state of sample annealing and the second being a 3D-growth, dominate the late stage close to saturation. From an Arrhenius plots of JMA coefficients for both processes we extracted the activation energies of the underlying dynamics which are 1.5(1) eV for disordering and 0.8(2) eV for ordering.

Influence of Intermediate Layer on Magnetic Properties of $L1_{0}$Ordered FePt Perpendicular Recording Media

The L10 ordered FePt thin films have been prepared by magnetron sputtering system on Cr85W15 underlayer at 500°C of substrate temperature. A 3 nm Pt or W thin interlayer was employed to modulate the magnetic properties of FePt films. The crystallographic relationship between the FePt thin film and the CrW underlayer was studied, and the dependence of FePt films structure and magnetic properties on the Pt or W interlayer was investigated. The M-H loop of the FePt films with Pt or W interlayer was analyzed by using a three-dimensional (3-D) micromagnetic model, with careful discussions of the tetragonal symmetry and the magneto-elastic anisotropy due to the stress in the film plane. The stress state in the films and its effect on magnetic properties were discussed.

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.

ＦｅＰｔ薄膜に対するＡｌ２Ｏ３添加効果

Recently much interest has been aroused by L10 ordered FePt thin films due to their large magnetocrystalline anisotropy, which is required for ultra-high-density magnetic recording media. The grain size of pure FePt films is fairly large, which can cause medium noise and a reduction of recording resolution. We prepared FePt and FePt-Al2O3 films by the in-situ ordering method, aiming to suppress the growth of grain size by transforming the disordered fcc phase into the L10 structure.

Textured growth of highly coercive L10 ordered FePt thin films on single crystalline and amorphous substrates

FePt films have been prepared by pulsed laser deposition at a temperature of 800 °C onto (001) oriented single crystalline (MgO, SrTiO3) as well as amorphous substrates (Si3N4, glass) with and without a (001) textured MgO buffer layer. Although all films have been prepared under identical conditions, significant differences in coercivity are observed. Very high values of up to 5.6 T have been measured for the epitaxial films, while on the amorphous substrates the coercivities range between 0.8 and 2.0 T. We analyze whether changes in intrinsic or extrinsic properties due to a modified microstructure are responsible for these differences.

Enhanced coercivity of L10 ordered FePt thin films fabricated by alternate monatomic layer deposition on stepped Pt(0 0 1)

Abstract L10 ordered FePt(0 0 1) thin films were prepared by alternating Fe and Pt monatomic layers on stepped Pt(0 0 1) surfaces at reduced temperature. The clear enhancement of coercivity has been observed due to the introduction of steps, which is considered to contribute to pinning domain walls.

Fabrication of L10 ordered FePt thin films with a canted easy magnetization axis on MgO (1 1 0) substrate

Abstract We have investigated the magnetic properties of highly coercive FePt films prepared on both MgO (0 0 1) and MgO (1 1 0) substrates with various film thicknesses ( t N ). FePt (0 0 1) films with perpendicular magnetization and FePt (1 0 1) films with a canted easy magnetization axis ( c -axis) were prepared on MgO (0 0 1) and MgO (1 1 0) substrates, respectively. At the critical thickness, where the film morphology changes from a particulate to a continuous state, a drastic decrease in the coercivity H c has been observed for the FePt (0 0 1) film, while no jump of H c has been observed for the FePt (1 0 1) films.