Heat Assisted Magnetic Recording for Areal Densities Beyond 1Tbit/in^2

The magnetic recording industry is keeping up with the ultra high demand of high capacity hard drives by improving the areal recording densities of these devices. Such imposing advancement in utilization and performance is due to successive scaling in the geometrical dimensions of the device. This progression has been truncated by the fundamental limit known as the superparamagnetic limit which occurs when bits of digital data are aggressively decreased that ambient heat demagnetizes them, leading to loss of the stored data.To overcome this problem, the use of large magnetic anisotropy energy density alloys is compulsory, but the write fields that are required by these alloys are prohibitively large, rendering these media effectively unwritable. Fortunately, heat assisted magnetic recording (HAMR) enables the use of the smallest possible thermally stable grains, irrespective of the ultra-large intrinsic anisotropy. HAMR exploits the substantial drop of coercivity of ferromagnetic material to a level attainable by the magnetic writing head when the disk temperature is elevated close to its Curie level, consequently enhancing the areal density dramatically. In this thesis, a theoretical and experimental study underlying the design of a heating element based on ultra-high-efficiency near-field optics suitable for extending areal densities beyond 1Tbit/in2 is presented. Near-field apertures are fabricated using focused ion beam milling and characterized via near-field optical microscopy. A breakthrough in the localization of adequate amount of heat into a 30 nm spot size is reported. HAMR demonstration is presented utilizing a customized spinstand tester, and the associated issues are thoroughly addressed

Design, Fabrication, and Characterization of Near-Field Apertures for 1 Tbit/in ^ Areal Density

Today, conventional magnetic recording schemes are coming to an end because of the superparamagnetic limit. Heat-assisted magnetic recording (HAMR) may ultimately extend data densities beyond 1 TB/in 2 . HAMR systems utilize the phenomenon during which the magnetic properties of the recording media could be locally modified via heating (optionally, by an optical source in the near field) to temperature in the vicinity of the Curie value of the media material. As a result, heat induced by the optical source can temporarily reduce the magnetic coercivity of high anisotropy material to a level attainable by the magnetic writing head, thus making it feasible to record on relatively small ultra-high anisotropy (and thermally stable) grains, consequently enhancing the areal density dramatically. The key challenge is to develop a near-field transducer capable of delivering over 50 nW into a spot diameter of 30 nm. Traditional fiber schemes are barely capable of 0.1 nW. To resolve the issue, a laser diode could be placed with the emitting edge only a few nanometers away from the recording media. The light can propagate through a nanoaperture on the surface of an aluminum-coated emitting edge. This paper will present an experimental study of recording characteristics of various near-field transducers fabricated via focused ion beam (FIB). To count the number of photons emitted in the near field, a scanning near-field optical microscopy system has been implemented. The experiments indicate that the FIB-fabricated transducers could deliver power of over a few microwatt into a 30-nm spot (Fig. 7)

Controlling multidomain states to enable sub-10-nm magnetic force microscopy

The letter reports experimental data to demonstrate magnetic force microscopy (MFM) with sub-10-nm resolution under ambient conditions. To achieve this record high resolution, multidomain states in a nanomagnetic probe were controlled. Two demagnetized (multidomain) FePt (45/55) films sputtered on a silicon probe and separated by an 8 nm thick MgO layer were further annealed at temperature of 650 degrees C to trigger the high-anisotropy L1(0) phase. A field of above 2 T was applied to drive the probes into a saturated "single-domain" state. The multidomain probes were equivalently compared with state-of-the-art conventional MFM probes via comparative imaging of benchmark magnetic recording disks

High-resolution and high-coercivity FePt L 1 0 magnetic force microscopy nanoprobes to study next-generation magnetic recording media

A cylindrical probe with almost perfectly flat plateaulike surface was focused ion beam (FIB) milled from an atomic force microscopy probe in order to create the required surface conditions for thin film deposition with finely controlled deposition/growth parameters. A composition of Pd(5 nm)/MgO(8 nm)/FePt(10 nm)/MgO(8 nm) was sputter deposited on the plateau probe, followed by deposition of a Pd (5 nm) protective layer. The plateau probe was then FIB-milled to produce a tip with a curvature radius of ∼ 25   nm . After annealing the probe at 650 ° C for ∼ 15   min to generate an ultrahigh anisotropy L 1 0 phase, magnetic force microscopy (MFM) imaging was performed with the probe on magnetic tracks with linear densities ranging from 200 to 1200 KFCI. The results show sub-20-nm lateral resolution in ambient conditions and magnetic tracks, which are otherwise invisible to standard MFM probes, are clearly evident with the FIB-fabricated FePt probe. With relatively high spatial resolution and coercivity values higher than 1 T, among other applications, this type of probe may be ideal for high-quality MFM study of next-generation recording media

Nanolasers to enable data storage beyond 10 Tbit ∕ in. 2

A focused ion beam (FIB) fabricated nanolaser is demonstrated to be able to focus light with power of over 250 nW into a 30 nm spot. To fabricate a nanolaser, a 100 nm thick aluminum film was deposited on the emitting edge of a diode laser. FIB was used to etch various apertures into the film. The power was measured by a scanning near-field optical microscope in the near-field regime with a 10 nm separation between the probe and the air bearing surface of the nanolaser. Out of four different shapes under study, "C"-shape aperture was found to have the highest throughput

Perpendicular Recording with Reduced Skew Angle Sensitivity

A detailed analysis to the problem of skew angle sensitivity in perpendicular magnetic recording is presented. A proposed analytical model is supported by numerical simulations with a commercial boundary element software program. According to the presented equivalent magnetic circuit model, a single pole recording head with a laminated composition involving two layers of different magnetic materials could be used to localize adequately strong magnetic field in the vicinity of the trailing edge of the recording head. It is shown that the recording field generated under each lamination layer is proportion to the relative magnetic permeability of the respective layer. Such localization of the magnetic flux results in substantially reduced skew angle sensitivity

Protein-based disk recording at areal densities beyond 10 terabits/in.(2)

The concept of optical protein-based memory has been of interest since the early 1970s. Yet, no commercially available protein-based memory devices exist. This review presents an analysis of the main challenges associated with the practical implementation of such devices. In addition, the discussion includes details on the potential of using the unparalleled properties of photochromic proteins by creating an optical data storage disk drive with unmatched features and, particularly, record-high data densities and rates

Magnetic force microscopy study of magnetic stripe domains in sputter deposited Permalloy thin films

A magnetic force microscopy based study on the formation of stripe domains in Permalloy ( Ni 80 Fe 20 ) thin films is presented. Our results show that the critical thickness for stripe domain initiation depended on the sputtering rate, the substrate temperature, and the film thickness. Beyond the stripe domain formation, an increase of the period of a highly ordered array of stripe domains was evident with increasing film thickness. Thin films sputtered at room temperature with thickness variation between ∼ 80 and ∼ 350 nm exhibited square-root growth dependency on stripe domains periodicity from ∼ 150 to ∼ 380 nm , respectively. Above a certain thickness, the domain period decreased and the periodicity deteriorated with the array becoming more random, which is a strong indicator of relatively high structural perpendicular anisotropy. To illustrate, Permalloy sputtered at 100 ° C initially showed linear dependence in stripe domain periodicity growth up until ∼ 650 nm thick films. The magnetic stripe domain structure began breaking down for thicker Permalloy films. Our data also suggested that the perpendicular anisotropy responsible for the formation of stripe domains might have resulted from strain-caused magnetostriction and the thin-film microstructure shape effect

Multilevel three-dimensional nanomagnetic recording

The paper outlines a review of multilevel (ML) and three-dimensional (3D) magnetic recording-a nanomagnetic recording technology suitable for information storage densities above 100 terabit/in(2). To comply with the multilevel signal configuration, ML magnetic recording exploits a 3D head/media system powered with next-generation data coding methods. It is believed that combined with novel information processing techniques, relatively cost-effective ML systems could be scaled down to a single-grain spin level thus enabling memory with effective areal densities above 100 Terabit/in(2)

Nanomagnetic probes to image patterned media for information densities beyond ten terabit-per-square-inch

The communication illustrates how focused ion beam-modified nanomagnetic probes could be used to image patterned media with the resolution of a few nanometers only and thus suitable for densities above 10 terabit/in(2) . To take advantage of the modified probes, the measured signal is deconvolved with the sensitivity field inherent to the probe. Focused ion beam is used to trim silicon probes into the probes with the adequate geometry to satisfy the requirements on the sensitivity field. The measurements indicate that the resolution of magnetic force microscopy could be made comparable with the resolution of atomic force microscopy