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

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

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

Ultrahigh Coercivity Magnetic Force Microscopy Probes to Analyze High-Moment Magnetic Structures and Devices

This letter addresses the fabrication and exploitation of ultrahigh coercivity magnetic force microscopy (MFM) probes to characterize high-magnetic moment nanostructures and devices. The L1 0 phase of FePt alloys together with CrRu and MgO seed layers are investigated as a method of increasing the coercivity of MFM probes to prevent their behavior as soft magnetic probes when used to image energized magnetic devices. The newly developed MFM probes, with coercivity higher than 11 kOe, are utilized to successfully analyze a modern perpendicular magnetic recording write head under various excitation conditions in order to perform writer saturation and remanence tests. The results include MFM micrographs of a fully energized magnetic writer, obtained with a probe-sample separation of only 10 nm

Multilevel-3D bit patterned magnetic media with 8 signal levels per nanocolumn.

This letter presents an experimental study that shows that a 3(rd) physical dimension may be used to further increase information packing density in magnetic storage devices. We demonstrate the feasibility of at least quadrupling the magnetic states of magnetic-based data storage devices by recording and reading information from nanopillars with three magnetically-decoupled layers. Magneto-optical Kerr effect microscopy and magnetic force microscopy analysis show that both continuous (thin film) and patterned triple-stack magnetic media can generate eight magnetically-stable states. This is in comparison to only two states in conventional magnetic recording. Our work further reveals that ferromagnetic interaction between magnetic layers can be reduced by combining Co/Pt and Co/Pd multilayers media. Finally, we are showing for the first time an MFM image of multilevel-3D bit patterned media with 8 discrete signal levels

Multilevel-3D Bit Patterned Magnetic Media with 8 Signal Levels Per Nanocolumn

This letter presents an experimental study that shows that a 3rd physical dimension may be used to further increase information packing density in magnetic storage devices. We demonstrate the feasibility of at least quadrupling the magnetic states of magnetic-based data storage devices by recording and reading information from nanopillars with three magnetically-decoupled layers. Magneto-optical Kerr effect microscopy and magnetic force microscopy analysis show that both continuous (thin film) and patterned triple-stack magnetic media can generate eight magnetically-stable states. This is in comparison to only two states in conventional magnetic recording. Our work further reveals that ferromagnetic interaction between magnetic layers can be reduced by combining Co/Pt and Co/Pd multilayers media. Finally, we are showing for the first time an MFM image of multilevel-3D bit patterned media with 8 discrete signal levels

Triple-stack ML-3D BPM.

<p>Schematic of the structure and desired magnetic properties (not to scale). The black arrows (binary “1″) and red arrows (binary “0″) denote the two possible magnetic states in each stack. Above the columns lies the binary representation and color coding for the eight possible magnetic states.</p

ML-3D BPM media fabrication process.

<p>(a) Sputter-deposition of the triple-stack ML-3D magnetic media composition (b) Spin-coat and bake HSQ (c) E-beam lithography (expose and develop patterns) (d) ICP etching of the naturally oxidized Ti layer (e) Ar-ion milling of the remaining composition to form the triple-stack ML-3D BPM.</p