Ultra-high Density Perpendicular Magnetic Recording Research Articles

The structural evolution in the growth process of FePt embedded in MgO matrix

FePt nanoparticles were successfully embedded in a single-crystal MgO matrix using a pulse laser deposition method. The growth behaviors were well controlled and monitored in situ by the reflection high-energy electron diffraction. The FePt nanoparticles and the MgO matrix were grown in three-dimensional island-like and two-dimensional layered modes, respectively. The embedded FePt nanoparticles do not affect the epitaxial growth of MgO layer. The epitaxial relationship between the FePt and MgO is [200]FePt ‖ [100]MgO. Due to the lattice mismatch between the MgO and FePt, the edge dislocation is observed in the interior of the FePt particles. The study on the structural evolution in the growth process of FePt embedded in the MgO matrix has benefited for not only fundamental research but also the applications of FePt ultrahigh-density perpendicular magnetic recording.

Investigation of FePt-SiO2-C granular film in columnar structure

We worked on a FePt granular film with a columnar structure, for the purpose of ultrahigh density perpendicular magnetic recording media. In experiments, a Fe53Pt47-SiO230%-C25% (10 nm) film was deposited on a silicon substrate with a MgO (12 nm) interlayer at 510 °C. The perpendicular coercivity of the film is 29 kOe, with a squareness of 1. Bright-field TEM images show that the FePt granular film has small and uniform grains of 8.3 ± 1.9 nm with a columnar structure. More work of high-resolution TEM imaging shows excellent L10 ordering inside the FePt grains. The measurement of remnant coercivity proves that it has an energy barrier of 290kBT at room temperature, meaning excellent thermal stability. We demonstrate FePt granular film to be a qualified candidate for high-density perpendicular magnetic recording media, and both SiO2 and C addition helps form columnar structure.

Perpendicular magnetic properties of ultrathin L10-Mn1.67Ga films grown by molecular-beam epitaxy

Materials with large perpendicular magnetic anisotropies (PMAs) have drawn great attention because of their potential applications in advanced spintronic devices such as spin-transfer-torque magnetic random access memory (STT-MRAM) and ultrahigh-density perpendicular magnetic recording. To date, a large variety of PMA materials have been investigated, such as L10-ordered FePt, CoPt granular films, Co/(Pt,Pd,Ni) multilayers, ultra-thin CoFeB alloys and perpendicularly magnetized Co2FeAl films. Among the various kinds of materials with PMA, MnGa film with L10-structure has received the most attention because it has large PMA (Ku～107 erg/cm3), ultralow Gilbert damping constant (0.008) and theoretically predicted high spin polarization (more than 70%). All these properties make L10-ordered MnGa a good candidate for spintronic devices such as STT-MRAM and spin-torque oscillators. Meanwhile, from the viewpoint of STT related spintronic device, it is necessary to fabricate ultrathin perpendicularly magnetized L10-MnxGa films to lower the critical current for magnetization reversal. However, up to now, in the main researches the ultrathin L10-MnxGa films have been grown on MgO substrates, which makes it difficult to integrate the MnGa-based magnetic tunnel junctions into the semiconductor manufacturing process.In this work, ultrathin L10-Mn1.67Ga films with different thickness values (1-5 nm) are grown on traditional GaAa (001) substrates by a molecule-beam epitaxy system. During the deposition, in situ streaky surface reconstruction patterns are observed from reflection high-energy electron diffraction, which implies high crystalline quality of the L10-Mn1.67Ga film. Only MnGa superlattice (001) and MnGa fundamental (002) peaks can be observed in the X-ray diffraction patterns in a range from 20 to 70, which means that the L10-Mn1.67Ga film is a good single-crystalline with c-axis along the normal direction. The magnetic properties of these films are measured by superconductor quantum interference device magnetometer in a field range of 5 T. The perpendicular M-H curves are almost square, while the in-plane curves are nearly hysteresis-free, each with a remnant magnetization (Mr) of around zero, which clearly evidences the PMA of the ultrathin L10-Mn1.67Ga film. Moreover, as the thickness of L10-Mn1.67Ga film decreases from 5 nm to 1 nm, the ratio of Mr/Ms also decreases from 1 to 0.72, which indicates that the PMA loses as thickness decreases. We also estimate the perpendicular anisotropy constant (Ku) from the relation Ku=Keff+2 Ms2, and the maximum Ku of 14.7 Merg/cm3 is obtained for the 5 nm MnGa film. Although the Ku decreases with thickness decreasing, a Ku value of 8.58 Merg/cm3 is observed in a 2 nm thick film. The obtained results are important for developing the L10-MnGa-based spin-transfer torque Gbit class magnetic random access memory.

All-optically configuring the inverse Faraday effect for nanoscale perpendicular magnetic recording.

Nanoscale reversal of the longitudinal magnetization (Mz) is highly desired in the ultrahigh density perpendicular magnetic recording. In this paper, an all-optical method to realize the reversal of Mz with an ultrasmall lateral size through configuring the inverse Faraday effect (IFE) is numerically proposed. This feature is achieved by optical coherent configuration of the IFE in the central and peripheral regions of the focal spot with opposite signs. By increasing the intensity of the peripheral regions to produce destructive interference, the lateral size of the reversed Mz smaller than 30 nm in one dimension in the central region can be achieved. This result is of vital importance for realizing ultrafast nanoscale perpendicular magnetic recording.

Overcoming the Trilemma Issues of Ultrahigh Density Perpendicular Magnetic Recording Media by L10-Fe(Co)Pt Materials

L10-ordered FePt and CoPt (collectively called L10- Fe ( Co ) Pt in this review) have become potential materials for future ultrahigh density perpendicular magnetic recording (PMR) media due to their high magnetocrystalline anisotropy, rendering small grains with high thermal stability. However, PMR media using such high anisotropy faces the well-known trilemma issues among thermal stability, signal-to-noise ratio (SNR), and writability. This paper will provide an overview of the impact of L10- Fe ( Co ) Pt on overcoming the superparamagnetic limit and balancing the trilemma issues for ultrahigh density PMR media. Here the research and development of L10- Fe ( Co ) Pt materials will be presented, from the perspectives of enhancing thermal stability, SNR and writability. Furthermore, we will provide some combined approaches to tackle the challenges in balancing the trilemma issues, focusing on materials engineering.

Synthesis of dense, single-crystallineCrO2 nanowire arrays using AAO template-assisted chemical vapor deposition

High-density, vertically alignedCrO2 nanowire arrays were obtained via atmospheric-pressure CVD assisted by AAO templates. TheCrO2 nanowire arrays show remarkably enhanced coercivity compared withCrO2 films or bulk. It was found that the length of the nanowires is greatly influenced by the porediameter of the AAO template used. The growth mechanism and the pore size dependence of theCrO2 nanowire arrays are discussed. The present method provides a useful approach for the synthesis ofCrO2 nanowire arrays. Such highly ordered nanowire arrays within an AAO template may haveimportant applications in ultrahigh-density perpendicular magnetic recording devices andthe mass production of spintronic nanodevices.

Granular L1 FePt:TiO2 (001) nanocomposite thin films with 5nm grains for high density magnetic recording

Fe Pt : Ti O 2 (001) thin films were deposited on CrRu∕MgO underlayers by dc magnetron cosputtering. The effects of TiO2 content on microstructure and magnetic properties of the epitaxial FePt (001) films were studied. Experimental results showed that even with 20vol% TiO2 doping, FePt films could keep a (001) preferred orientation and perpendicular anisotropy. The FePt:TiO2 (001) film with 5nm grain size, adjustable coercivity, and reduced exchange coupling was obtained by doping 20vol% TiO2 into FePt film, showing great potential as low noise ultrahigh density perpendicular magnetic recording media.

The (0 0 1)-oriented [BN/CoPt] n/Ag composite films deposited on glass substrates

[BN/CoPt] 5/Ag composite films are grown on glass substrates by using magnetron sputtering, then annealed at 550 and 600 °C for 30 min. We found that Ag underlayer together with the suitable concentration of BN matrix can provide a driving force for the chemical ordering of the L1 0 CoPt phase, as well as give an opportunity for the (0 0 1)-oriented growth of CoPt grains. The triple system of [BN2.5 nm/CoPt3 nm] 5/Ag(10 nm) films have a good perpendicular oriented growth, a low intergranular interactions, as well as a high perpendicular anisotropy, will be a potential candidate for ultrahigh-density perpendicular magnetic recording media.

Fabrication of integrated arrays of ultrahigh density magnetic nanowires on glass by anodization and electrodeposition

Integrated nanowire arrays of Fe–Pt, Co–Pt, and Ni–Pt alloys were successfully fabricated on glass substrates by successive anodization and electrodeposition. Porous alumina films, which were formed from an aluminum layers sputter-deposited on glass substrates covered with transparent oxide conductive films, were used as template-electrodes to deposit various magnetic alloys (Fe–Pt, Co–Pt, and Ni–Pt) in the nanopores by a cathodic electrodeposition, thus leading to integrated nanowire arrays with ultrahigh densities of (0.6–2.1) × 10 15 wire m −2. The as-deposited nanowires of Fe–Pt, Co–Pt, and Ni–Pt alloys are polycrystalline and composed of fine crystals (4–7 nm across) of chemically ordered tetragonal FePt, CoPt, or NiPt phase. The integrated nanowire arrays may be the promising candidate materials for ultrahigh density perpendicular magnetic recording media in terabits per square inch regime, due to the predictable enhanced perpendicular magnetic performance after appropriate annealing.

Spinel ferrite Co/-λFe/sub 2/O/sub 3/ perpendicular media on exchange-coupled underlayers

In ultra-high density perpendicular magnetic recording, double-layered media consisting of a recording layer on a soft magnetic layer are required. For the recording layer, spinel ferrite Co-γFe/sub 2/O/sub 3/ films have been investigated. The films have advantages of high coercivity, high stability without protective layer, and low noise performance. For the soft magnetic layer, exchange-coupled CoZrNb/CoSm underlayers have been studied. The CoSm hard magnetic layer pins the domains of amorphous CoZrNb soft magnetic layer effectively, and decreases the noise coming from the soft magnetic layer. Also, signal stability under stray fields and high frequency responses have been observed in the media consisting of a CoCrTa recording layer on the CoZrNb/CoSm underlayers. In this study, the preparation and properties of Co-γFe/sub 2/O/sub 3/ media, combined with exchange-coupled CoZrNb/CoSm underlayers, are described.

Structural and magnetic properties of NdFeB thin films sputtered on W underlayers

The NdFeB thin films are fabricated by a DC magnetron sputtering system. We find W underlayer is favorable to pseudomorphic growth of Nd 2Fe 14B crystallites with predominant c-axis perpendicular alignment. Through manipulating the sputtering parameters, this kind of pseudomorphic growth can be effective in a certain film thickness range. In our case, the crucial thickness value is estimated to be about 30 nm, which is thick enough for application of the ultra-high density perpendicular magnetic recording media. Beyond this range, misfit dislocation will be formed in the films, the films become more soft due to the formation of soft phases. We also discuss the magnetization reverse mechanism of the interested film with the thickness of 15 nm. Its magnetization reverse process is found to be mainly controlled by magnetization incoherent rotation.

Design consideration of ultrahigh-density perpendicular magnetic recording media

Design consideration of double-layered perpendicular magnetic recording media for ultrahigh-density recording was studied based on a micromagnetic model. It was found that the introduction of an appropriate exchange coupling between grains remarkably improves the recording resolution of the media. The essential role of the exchange coupling could be understood that it increases the perpendicular M-H loop slope, which has the same contribution to the resolution as the head field gradient. Large values for the product of the M-H loop slope parameter and the head field gradient are expected to result in small transition widths less than 10 nm. Consideration of thermal stability of the media including effects of the demagnetizing field and the M-H loop slope suggested that Co-Cr based media would meet the magnetic properties for recording of 200 Gb/in/sup 2/ but may not for higher densities. Media with higher anisotropy fields like Fe-Pt would be the candidate.

Thin film properties by facing targets sputtering system

In this study, film thickness distribution and c-axis crystalline orientation of deposited thin films were studied after preparing Co–Cr thin films, a promising ultra-high density perpendicular magnetic recording media, with a facing targets sputtering (FTS) apparatus. Electrical discharge characteristics needed for the optimum operation of sputter device was also studied in order to prepare thin films of superior c-axis crystalline orientation with FTS method (apparatus) in which thin film of fine quality can be formed because temperature increase of substrate due to the bombardment of high-energy particles can be restrained. As a result of the study, it is confirmed that the FTS method can give stable working under broad magnetic field and range of gas pressure and stable electrical discharge under low Ar gas pressure. Film thickness of prepared thin film shows fairy regular distribution and could obtain good thin films whose dispersion angle of c-axis crystalline orientation is about 3.5°.

Preparation of Co–Cr–Ta films with nano-size magnetic domains for 1000 kfci media

In order to achieve the formation of nanometer(nm)-size ferromagnetic domains in the recording layers for 1000 kfci media, Co–Cr–Ta thin films for ultra-high density perpendicular magnetic recording layers were deposited using a plasma enhancing type of facing targets sputtering (FTS) apparatus by optimizing the film thickness t F, the substrate temperature T s, the residual gas pressure P res and the sputtering Ar pressure P Ar. The specimen Co 76Cr 24 films with t F of 50 nm were deposited on glass disks at T s of 230°C, P Ar of 0.2 mTorr and P res of 0.5 μTorr. Investigation of these films indicated that they were composed of highly c-axis oriented HCP crystallites, in which the isolated ferromagnetic areas with lower Cr content C Cr were uniformly distributed in the paramagnetic host matrix with higher C Cr. Diameter of lower C Cr areas was as small as 3–5 nm. The perpendicular coercivities H c⊥ of the initial growth region, the whole film and the surface region were 1100, 1900 and 2700 Oe, respectively. Since these films revealed voidless microstructure and nm-size magnetic zones, they may be adaptable for the fabrication of magnetic recording media at ultra-high density around 1000 kfci (10 Gb/in 2).

Nano-size magnetic crystallite formation in Co-Cr thin films for perpendicular recording media

In order to understand the formation of nano-size magnetic domains in Co/sub 76/Cr/sub 24/ thin films for ultra-high density perpendicular magnetic recording, film thickness and sputtering gas pressures were investigated using a facing target sputtering (FTS) apparatus. Investigations of these films showed thy were composed of highly oriented hcp crystallites with lower Cr content (C/sub Cr/) of isolated ferromagnetic areas uniformly distributed in the higher C/sub Cr/ host paramagnetic matrix. The diameter of the lower C/sub Cr/ areas in these films was between 3-5 nm. The perpendicular coercivity in the surface region was greater than 2400 Oe. Consequently, this film is considered to be a good candidate for perpendicular magnetic recording densities approaching 1000 Kfci (10 Gb/in/sup 2/).

Computer simulation of ultrahigh-density perpendicular magnetic recording

The possibility of ultrahigh-density recording higher than 10 Gb/in.2 with perpendicular magnetic recording is investigated by computer simulation for a ring-type head and single-layer medium combination. A nucleation model is used as a media model because it incorporates a nucleation site, which causes irreversible magnetization switching. Fundamental read–write characteristics are found to be entirely different from those of longitudinal recording. Recorded magnetization strongly depends on head field strength; the maximum magnetization appears around the head field strength of media coercivity, and beyond this the recorded magnetization decreases abruptly. Spacing loss in the recording process also depends on head field strength and recording density. However, saturation recording can be attained even at an ultrahigh recording density of 600 kFCI with a spacing of 30 nm. Also, a higher signal-to-noise ratio than in longitudinal recording can be obtained by introducing weak intergrain exchange interaction with a relatively large grain size in the media film. This suggests that perpendicular magnetic recording is stable in thermal fluctuation. © 1996 American Institute of Physics.