Nissim Amos

Effect of nitrophenyl functionalization on the magnetic properties of epitaxial graphene.

Graphene displays unprecedented electronic properties including room-temperature ballistic transport and quantum conductance, and because of its small spin-orbit interaction, graphene has the potential to function as the building block of future spintronic devices. Theoretical calculations indicate that a defective graphene sheet will be simultaneously semiconducting and magnetic; thus it would act as a room-temperature magnetic semiconductor. Recently, ferromagnetic ordering at room temperature has been observed by magnetometry measurements on bulk samples of reduced graphene oxide.

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 (Ni80Fe20) 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 ∼350nm exhibited square-root growth dependency on stripe domains periodicity from ∼150to∼380nm, 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 ∼650nm thick films. The magnetic stripe domain structure began ...

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 °C to trigger the high-anisotropy L10 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.

Study of Co/Pd multilayers as a candidate material for next generation magnetic media

We report a combinatorial synthesis study on the magnetic properties of sputter-deposited Co/Pd multilayers with high perpendicular anisotropy and high remnant squareness for magnetic media applications such as magnetic logic systems, bit patterned media, magneto-optical recording, and multilevel three-dimensional (3D) magnetic media. The perpendicular magnetic anisotropy in the multilayers originates from the interfacial anisotropy of the alloylike structure. The deposition conditions and subsequent microstructures of the multilayers are critical factors to determine the magnetic properties of the media. We investigated the dependence of the magnetic properties on the thickness of Co and Pd layers the number of Co/Pd bilayers. For instance, we found that a 0.26-nm-thick layer of Co would produce the highest coercivity value if paired with a 0.55-nm-thick Pd layer. Our results revealed that an Ar+ milling could significantly increase the coercivity of the multilayer media. Further, we discovered that we c...

Magneto-optical Faraday effect in nanocrystalline oxides

Magneto-optical materials have widespread applications in communication and optical devices. Besides existing applications such as optical diodes, untapped potential applications could be accessed should magneto-optical properties be improved such that smaller magnetic fields can be employed. Here we present an efficient method for fabricating oxide materials that possess excellent optical and magnetic properties—they are transparent to visible light yet have high magnetic susceptibility. Combined, these properties produce large Faraday rotations; the measured Verdet constant is >−300 rad T−1 m−1 at 632.8 nm, a high value for a thick, optically transparent material. Because this Verdet constant is more than twice that of the state of the art material, these nanocrystalline oxides produce polarized light rotations with less than half the applied magnetic field necessary. They are made by densifying rare earth nanocrystalline powder into dense, large-sized bodies using an electric current activated techniqu...

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.

High-resolution and high-coercivity FePtL10 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 L10 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 ...

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

A focused ion beam (FIB) fabricated nanolaser is demonstrated to be able to focus light with power of over 250nW into a 30nm spot. To fabricate a nanolaser, a 100nm 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 10nm 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.

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

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/in2. 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).

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This letter addresses the fabrication and exploitation of ultrahigh coercivity magnetic force microscopy (MFM) probes to characterize high-magnetic moment nanostructures and devices. The L10 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.