Sakhrat Khizroev

Recording physics of perpendicular media: soft underlayers

The results of both theoretical and experimental studies of some of the key aspects of the recording physics specific to perpendicular media with a soft underlayer are presented. Some of the discussed issues are the material requirements for the preferred soft underlayer design such as the role of magnetic anisotropy, the proper choice of the magnetic moment, and the control of the soft underlayer noise.

Targeted and controlled anticancer drug delivery and release with magnetoelectric nanoparticles.

It is a challenge to eradicate tumor cells while sparing normal cells. We used magnetoelectric nanoparticles (MENs) to control drug delivery and release. The physics is due to electric-field interactions (i) between MENs and a drug and (ii) between drug-loaded MENs and cells. MENs distinguish cancer cells from normal cells through the membrane’s electric properties; cancer cells have a significantly smaller threshold field to induce electroporation. In vitro and in vivo studies (nude mice with SKOV-3 xenografts) showed that (i) drug (paclitaxel (PTX)) could be attached to MENs (30-nm CoFe2O4@BaTiO3 nanostructures) through surface functionalization to avoid its premature release, (ii) drug-loaded MENs could be delivered into cancer cells via application of a d.c. field (~100 Oe), and (iii) the drug could be released off MENs on demand via application of an a.c. field (~50 Oe, 100 Hz). The cell lysate content was measured with scanning probe microscopy and spectrophotometry. MENs and control ferromagnetic and polymer nanoparticles conjugated with HER2-neu antibodies, all loaded with PTX were weekly administrated intravenously. Only the mice treated with PTX-loaded MENs (15/200 μg) in a field for three months were completely cured, as confirmed through infrared imaging and post-euthanasia histology studies via energy-dispersive spectroscopy and immunohistochemistry.

Perpendicular magnetic recording: Writing process

In this article, a detailed overview of the methodology to design a write transducer for recording onto perpendicular media at areal densities beyond 1 Tbit/in.2 is presented. The two basic modes of perpendicular recording, single-layer recording media in combination with a ring type head and double-layer recording media with a soft underlayer in combination with a single pole head, are compared with each other theoretically and experimentally. Moreover, perpendicular recording is compared to longitudinal recording from the perspective of the writing process. The system efficiency is redefined for perpendicular recording to take into account the critical role of the soft underlayer. The effects of using “soft” magnetic shields around the trailing pole are analyzed. It is shown that at least a factor of 2 increase in the field can be obtained at areal densities beyond 500 Gbit/in.2 if shields are used. Such an open issue as the skew angle sensitivity in perpendicular recording is analyzed. It is shown that...

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.

Recording heads with track widths suitable for 100 Gbit/in/sup 2/ density

Focused ion beam etching has been used to trim both longitudinal and perpendicular recording heads with track widths as narrow as 60 nm. 3D boundary element modeling has been used to optimize trimming parameters. Tracks written with the trimmed heads using spin-stands and imaged using magnetic force microscopy were as narrow as 100 nm.

Room-temperature magnetic ordering in functionalized graphene.

Despite theoretical predictions, the question of room-temperature magnetic order in graphene must be conclusively resolved before graphene can fully achieve its potential as a spintronic medium. Through scanning tunneling microscopy (STM) and point I-V measurements, the current study reveals that unlike pristine samples, graphene nanostructures, when functionalized with aryl radicals, can sustain magnetic order. STM images show 1-D and 2-D periodic super-lattices originating from the functionalization of a single sub-lattice of the bipartite graphene structure. Field-dependent super-lattices in 3-nm wide “zigzag” nanoribbons indicate local moments with parallel and anti-parallel ordering along and across the edges, respectively. Anti-parallel ordering is observed in 2-D segments with sizes of over 20 nm. The field dependence of STM images and point I-V curves indicates a spin polarized local density of states (LDOS), an out-of-plane anisotropy field of less than 10 Oe, and an exchange coupling field of 100 Oe at room temperature.

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 ...

Direct observation of magnetization switching in focused-ion-beam-fabricated magnetic nanotubes

In this letter, a direct measurement of “easy” magnetization switching indicating zero-magnetization remanence in a magnetic probe with a cross section as narrow as 60×60 nm2, and as tall as 750 nm, is presented. Magnetic force microscopy was utilized to test focused-ion-beam-fabricated nanomagnetic probes. The data directly indicate that unlike a regular solid probe, a probe with a tubelike ending (nanotube) provides substantially “easier” switching.

Considerations In The Design Of Probe Heads For 100 Gbit/in/sup 2/ Recording Density

Thin film perpendicular playback yoke-GMR heads capable of reading at a density of 100 Gbit/in/sup 2/ have been designed using 3D boundary element reciprocity modeling. Two basic head types are considered, a single-pole and a ring-type geometry. The influence on the playback voltage and D/sub 50/ of the throat height, fly height, and permeability are studied. Isolated pulse response, roll-off curves, and off-track profiles are calculated. Media with and without a soft underlayer are also considered. The simulations show that of the designs studied the ring head in combination with the media without a soft underlayer has playback properties suitable for this density.

Recording physics of perpendicular media: hard layers

The results of both theoretical and experimental studies of some of the key issues related to the hard layer in perpendicular magnetic recording are presented. Among the discussed issues are the guidelines and underlying physics for choosing the optimized recording layer parameters such as thickness, specific magnetic properties, types of recording layer material, etc. Special attention is given to the physical phenomena and parameters that define the optimum thickness of the recording layer. To stress the specific aspects of the recording physics native only to perpendicular recording, a comparison between perpendicular and longitudinal media is carried out throughout the work.