Energy-assisted Magnetic Recording Research Articles

Magnetic printing characteristics of burst signals by using double magnet master media

In this study, the magnetic printing characteristics of burst signals with double magnet master (DMM) media, which consists of hard and soft magnet patterns corresponding to the burst signals, onto energy-assisted magnetic recording (EAMR) media was investigated by the micromagnetic simulation. For comparison, the magnetic printing characteristics with the conventional master media, which includes only soft magnet patterns, was also calculated. The magnetic film patterns of each master media transfer automatic-gain-control (AGC) and burst parts to the recording medium. The burst signals was amplitude AB-burst patterns, which consists of the repeated pattern region and blank area without burst patterns. Two possible master media structures of DMM media were considered, which are herein called positive- and negative- DMM media. By utilizing the positive-DMM, which spatially divides soft magnets, the AGC and the burst signals can be clearly printed, comparing with the conventional master media. While the negative-DMM is insufficient to print burst signals because the blank area without burst patterns has some non-recorded clusters. Thus, the positive-DMM are feasible for the magnetic printing of burst signals. The clear printing onto EAMR media is expected to be obtained by the optimum non-magnetic separator thickness and the optimum printing field. Therefore, the magnetic printing with positive DMM master is promising onto EAMR media.

Combinatorial dependence of magnetic printing characteristics in double magnet master media for energy-assisted magnetic recording

In this study, the combinatorial dependence in double magnet master for energy-assisted magnetic recording was investigated by the micromagnetic framework. Four kinds of master media, which are soft single magnet (SSM), hard single magnet (HSM), soft double magnet (SDM) and hard double magnet (HDM), were compared. Comparing single magnet and double magnet master media, more adequate combination of double magnet master media was discussed. The HSM, SDM, and HDM master media can write line/space (L/S) pattern with bit length of 20 nm, while the double magnet master media can clearly print L/S patterns comparing with single magnet in case of 10 nm. For higher coercivity EAMR media, the larger printing field causes larger recording field difference by utilizing SDM master media while in case of HDM the recording field difference is almost constant even if the printing field increases. As a result, since the recording field difference of SDM becomes larger than that of HDM as the printing field strengthens, thus, SDM master media can write the servo signals onto higher coercivity EAMR media. It was concluded that it is important for the low coercivity parts of double magnet master media to have a larger saturation magnetization due to enhancement of large recording field difference.

Master Structure Dependence of Double Magnet Master on Performance of Magnetic Printing Onto Energy-Assisted Magnetic Recording Media

The dependence of double magnet master (DMM) printing characteristics on master thickness and non-magnetic separator (NMS) thickness is investigated using micromagnetic simulation. It is found that the recording field difference saturates when the master thickness reaches the bit length. The NMS, which separates the two magnetic materials of the DMM, shifts the maximum points of the recording field distribution into the softer magnet regions, decreasing the island-like non-reversed regions, thus enhancing the printing performance. The effective switching field is important for understanding magnetic printing characteristics. The printed magnetization distributions are in accordance with the switching field distribution of the recording field generated by the DMM. Therefore, optimizing the master thickness and NMS thickness effectively improves the DMM printing characteristics for various servo patterns.

Sub-Nanosecond Switching of Spin-Transfer-Torque Device for Energy-Assisted Perpendicular Magnetic Recording

A giant magnetoresistance (GMR) based spin-transfer-torque (STT) device is built into the top gap of the writer of a magnetic write head for energy assisted magnetic recording. Magnetization of the spin-torque layer (STL) in the STT device can be aligned opposite to the magnetic field direction inside the top gap and thus increases the write field seen by the media. A method of high-speed, real-time measurement of the switching dynamics of the STL when the writer switches polarity is developed. We demonstrate that the switching time of STL can be 300 picoseconds or less, we also show that STL dimensions can strongly affect the switching speed of the STL and are important design parameters that need to be optimized for performance and reliability trade-offs. The measurement results are compared to micro-magnetic simulation. They show qualitative agreement with some discrepancies, possible causes are discussed.

Write Head With DC Current-Driven Energy-Assisted Magnetic Recording

Write Head With DC Current-Driven Energy-Assisted Magnetic Recording

Double Magnet Master Media for Magnetic Printing Onto Energy-Assisted Magnetic Recording Media

The magnetic printing onto energy-assisted magnetic recording (EAMR) media by utilizing double magnet master (DMM) media has been demonstrated. The DMM media is effective for improving printing characteristics by enhancing recording field with two different magnetic patterns that consist of high coercivity and low coercivity magnets. The magnetization distributions and printing performances (PPs) for magnetic printing onto EAMR media were evaluated by the micromagnetic simulation. The DMM can clearly print the L/S and checkerboard patterns onto EAMR media, and the DMM PP was superior to that of the conventional master media. The DMM printing could write the servo-signals onto the EAMR media with the coercivity of up to 30 kOe. The narrower switching distributions of grains in EAMR media enhances the printing characteristics. The potential of magnetic printing with DMM media was revealed for writing the servo-signals onto the EAMR media.

Tape in the cloud—Technology developments and roadmaps supporting 80 TB cartridge capacities

Tape, which is the storage of magnetic bits on flexible 0.5” wide media, provides critical data storage needs for the Cloud as evidenced by continued growth in exabyte shipments of tape products. This paper outlines the present storage landscape environment for tape, HDD, and NAND flash, describes the tape roadmap for capacity improvements, and presents recording data on narrow track, 32 channel, TMR tape heads spanning read sensor widths from 1.0 μm to 0.20 μm illustrating the potential for 80 TB cartridge operation. Critically, future improvements in tape areal density and tape cartridge capacity are expected to be achieved from evolutionary developments in head/media technology, not requiring revolutionary developments, such as energy assisted magnetic recording technologies required by HDD strategies.

Signal Processing and Coding Techniques for 2-D Magnetic Recording: An Overview

Two-dimensional magnetic recording (TDMR) is an emerging storage technology that aims to achieve areal densities on the order of 10 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , mainly driven by innovative channels engineering with minimal changes to existing head/media designs within a systems framework. Significant additive areal density gains can be achieved by using TDMR over bit patterned media (BPM) and energy-assisted magnetic recording (EAMR). In TDMR, the sectors are inherently 2-D with reduced track pitch and bit widths, leading to severe 2-D intersymbol interference (ISI). This necessitates the development of powerful 2-D signal processing and coding algorithms for mitigating 2-D ISI, timing artifacts, jitter, and electronics noise resulting from irregular media grain positions and read-head electronics. The algorithms have to be eventually realized within a read/write channel architecture as a part of a system-on-chip (SoC) within the disk controller system. In this work, we provide a wide overview of TDMR technology, channel models and capacity, signal processing algorithms (detection and timing recovery), and error-correcting codes attuned to 2-D channels. The innovations and advances described not only make TDMR a promising future technology, but may serve a broader engineering audience as well.

Magnetic characteristics and nanostructures of FePt granular films with GeO2 segregant

To realize a granular film composed of L10-FePt grains with high uniaxial magnetic anisotropy energy, Ku, and segregants for energy-assisted magnetic recording, a FePt-GeO2/FePt-C stacked film was investigated in the engineering process. The FePt-GeO2/FePt-C stacked film fabricated at a substrate temperature of 450 °C realized uniaxial magnetic anisotropy, Kugrain, of about 2.5 × 107 erg/cm3, which is normalized by the volume fraction of FePt grains, and a granular structure with an averaged grain size of 7.7 nm. As the thickness of the FePt-GeO2 upper layer was increased to 9 nm, the Ku values were almost constant. That result differs absolutely from the thickness dependences of the other oxide segregant materials such as SiO2 and TiO2. Such differences on the oxide segregant are attributed to their chemical bond. The strong covalent bond of GeO2 is expected to result in high Ku of the FePt-GeO2/FePt-C stacked films.

Acoustically Assisted Magnetic Recording: A New Paradigm in Magnetic Data Storage

A new paradigm in energy-assisted magnetic recording, acoustically assisted magnetic recording (AAMR), is investigated. In this approach, a surface acoustic wave (SAW) is applied to a magnetostrictive recording medium to temporarily lower its coercivity below the write field. Akin to other energy-assisted recording technologies, AAMR provides a strategy to enable writing on high-coercivity media required for thermal stability in high-density disk drives. Using a contact recording tester, it is demonstrated that the write current needed to record data on a galfenol film is reduced in the presence of SAWs. Further, it is shown that standing and focused acoustic waves can, respectively, be used to lower the coercivity in selected regions on the medium.

Giant temperature dependence of the spin reversal field in magnetoelectric chromia

Magnetic field-induced reversal of surface spin polarization for the magnetoelectric antiferromagnet chromia is studied via magnetometry in (0001)-textured thin films of various thicknesses. Reversal solely by magnetic means has been experimentally evidenced in sufficiently thin films. It sets the field-response of chromia films apart from bulk behavior, where switching between time-reversed single domain states requires the simultaneous presence of electric and magnetic fields. In our detailed experiments, we furthermore observe a giant sensitivity of the coercive field on temperature, thus, indicating the potential of magnetoelectric antiferromagnets as promising candidates for energy assisted magnetic recording media.

Microfocal lens for energy-assisted magnetic recording technology

In this Letter an original method is proposed to assist optical coupling in energy-assisted magnetic recording systems by introducing a microfocal lens. Simulation results show that the lens effectively reduces the incident light spot size to subwavelength scale, which benefits the magnetic recording density. The proposed microfocal lens can be manufactured at low cost because its fabrication is compatible with the conventional magnetic read/write head process.

Thermal Stability of Ultrathin Amorphous Carbon Films for Energy-Assisted Magnetic Recording

Energy-assisted magnetic recording (EAMR) uses a laser-optical system integrated into the magnetic head to heat locally a fine-grained material of high magnetic anisotropy energy density above its Curie temperature, and store single bits in very small areas without being limited by the superparamagnetic effect. However, localized laser heating may affect the thermal stability of the carbon overcoat of the hard disk. To examine the effect of laser heating on the overcoat thermal stability, ultrathin amorphous carbon (a-C) films of similar thickness (~ 3.6 nm) synthesized by filtered cathodic vacuum arc (FCVA) and chemical vapor deposition (CVD) were subjected to repetitive heating under different laser powers. Carbon hybridization and surface roughness of the a-C films were examined by Raman spectroscopy and atomic force microscopy, respectively. For the laser power range studied (150-300 mW), a-C films produced by the FCVA technique demonstrated superior thermal stability than CVD films of similar thickness. To investigate the possibility of further reducing the magnetic spacing, thinner (~ 0.9 nm) a-C films deposited by the FCVA method were subjected to the same laser heating conditions. Although the thermal stability of the FCVA-synthesized a-C films exhibited thickness dependence, even the thinner (~ 0.9 nm) FCVA film demonstrated higher thermal stability than the much thicker (~ 3.6 nm) CVD film. The results of this study illustrate the high potential of FCVA as a coating method for EAMR.

Atomic level micromagnetic model of recording media switching at elevated temperatures

An atomic level micromagnetic model of granular recording media is developed and applied to examine external field-induced grain switching at elevated temperatures which captures nonuniform reversal modes. The results are compared with traditional methods which employ the Landau–Lifshitz–Gilbert equations based on uniformly magnetized grains with assigned intrinsic temperature profiles for M(T) and K(T). Using nominal parameters corresponding to high-anisotropy FePt-type media envisioned for energy assisted magnetic recording, our results demonstrate that atomic-level reversal slightly reduces the field required to switch grains at elevated temperatures, but results in larger fluctuations, when compared to a uniformly magnetized grain model.

Switching field distribution and transition width in energy assisted magnetic recording

In order to achieve higher areal density, magnetization transition width must be reduced. This requires small media switching field distribution (SFD). Here we explore SFD and transition width in heat assisted magnetic recording and microwave assisted magnetic recording. We reveal that for energy assisted magnetic recording, additional SFD broadening exists as compare to conventional perpendicular recording. We show the effect of SFD broadening on transition width and the implications to the magnetic recording system as the areal density increases.

Perspectives of Magnetic Recording System at 10 Tb/in$^{2}$

The magnetic recording technology started to face superparamagnetism at the areal density of a few 10 s Gb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . To postpone this physical limitation, the recording configuration has to be changed by either increasing the write capability or reducing the grain number per bit. It had been switched from conventional longitudinal recording to perpendicular recording and will continue changing to other new recording configurations in the future. Beyond 1 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> areal density, the recording system is possible to be either the energy-assisted magnetic recording (EAMR) or the bit patterned media (BPM). At 10 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> areal density, one of them alone may not be enough and most people believe that EAMR and BPM have to be combined together to make it happen. In this paper, we explore the possible recording configurations at 10 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and calculate the corresponding design parameters of the recording system.

Ultrahigh-Hc granular media with [CoB∕Pt]n multilayer film sputtered under Ar+O2 atmosphere

We developed a [Co∕Pt]n multilayer film for fabricating a perpendicular recording film with an ultrahigh coercivity (Hc). Adding boron into each Co layer and further introducing O2 during deposition yielded a high Hc of 1200kA∕m. Transmission electron microscopy and magnetic measurements suggested that the intergranular exchange coupling was reduced to the level of conventional CoCrPt-oxide granular films. The [CoB∕Pt]n+O multilayer film is applicable to a hard magnetic layer in exchange-coupled composite media as well as energy-assisted magnetic recording media.