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Bloomington, MN, United States

Sharma A.,University of Minnesota | Zhu Y.,University of Minnesota | Reddy M.,University of Minnesota | Hubel A.,University of Minnesota | And 3 more authors.
Springer Proceedings in Physics | Year: 2014

This paper reviews the synthesis of magnetic multilayerd nanowires that have a wide range of applications. Specifically of interest in this review are the applications of magnetic manipulation and separation of cells, which are important for potential cancer therapies. Compared to other magnetic nanoparticles in use today, the nanowires have the advantage of being ferromagnetic and also having high aspect ratios that enable barcoding. These nanobots are synthesized inside nanoporous oxide templates in large batches (1012 per square inch), and they can be composed of any magnetic metal, alloy, or multilayer that can be electroplated. Specific details for the electrochemistry of Galfenol deposition are given. Galfenol is an exciting new magnetostrictive material with durable mechanical properties. Next, a protocol is described for full removal of the growth contact prior to release of the nanobots from their oxide template. This mitigates aggregation which inhibits cellular uptake. Feasibility of manipulation and separation was shown using canine bone cancer (os-teosarcoma) cells which internalized the nanobots, enabling magnetic cellular control. In addition, initial toxicity studies indicate that the nanobots are not cytotoxic. These studies merely scratch the surface of the potential use of nanobots for diagnosis and therapy in the near future. © Springer International Publishing Switzerland 2014. Source

Bhat V.,University of Kentucky | Woods J.,University of Kentucky | Hastings J.T.,University of Kentucky | De Long L.E.,University of Kentucky | And 5 more authors.
Proceedings - 2011 International Conference on Electromagnetics in Advanced Applications, ICEAA'11 | Year: 2011

We have performed broad-band (10 MHz-20 GHz) and tuned cavity (9.7 GHz) ferromagnetic resonance measurements on permalloy thin films patterned with square lattices of circular, square and diamond-shaped antidots of various sizes and separations. We observe remarkably reproducible mode structures in the low-frequency, hysteretic regime in which various domain wall patterns and unsaturated magnetization textures exist and are strongly affected by the geometry of the antidot lattice. The field, frequency and angular dependences of the observed modes (some of which have not been previously observed) are generally in good agreement with our micromagnetic simulations. © 2011 IEEE. Source

Bhat V.,University of Kentucky | Woods J.,University of Kentucky | De Long L.E.,University of Kentucky | Hastings J.T.,University of Kentucky | And 5 more authors.
Physica C: Superconductivity and its Applications | Year: 2012

Previous ferromagnetic resonance (FMR) studies of ferromagnetic (FM) thin films patterned with antidot (AD) arrays have generally avoided the low-field, hysteretic regime that is dominated by irreversible domain wall (DW) dynamics in unpatterned films. Moreover, FM vortices have not yet been identified and systematically studied in films patterned with AD lattices (ADLs). We have studied DC magnetization and broad-band FMR data for permalloy thin films of thickness t ≈ 25 nm, patterned with square lattices of square-shaped AD of width D and separation d = 1000 nm. We observe highly reproducible magnetic hysteresis curves and FMR spectra in the low-field reversal regime (i.e., applied magnetic fields H < H C, where H C is the coercive field), which indicates the ADL enforces a reproducible evolution of spin textures compared to the more random behavior of DW evolution in unpatterned films. The width of the reversal regime (2H C) and the field separation between observed FMR modes increases with D for a fixed separation d. Our micromagnetic simulations suggest these effects are consequences of both edge pinning of moments by individual AD, or DW pinning by the extended ADL, which involves two distinct length scales L ≈ d and L ≫ d, respectively. FM vortices are observed in our simulations, and their stability sensitively depends upon the AD size and applied magnetic field history. © 2012 Elsevier B.V. All rights reserved. Source

Jalli J.,University of Alabama | Hong Y.-K.,University of Alabama | Bae S.,University of Alabama | Lee J.-J.,University of Alabama | And 8 more authors.
Journal of Applied Physics | Year: 2011

Single crystals of Zr-substituted Zn-Y (Zr-ZnY; Ba2Zn 2ZrxFe12-xO22) were grown from the flux system of BaCO3 and B2O3 by a high temperature slow cooling flux method. X-ray diffraction pattern confirmed the crystal structure with Zn-Y composition. The single crystals were characterized for magnetic and microwave properties. The measured anisotropy field (HA) and the in-plane magnetization (σs) are 13 kOe and 52.0 emu/g, respectively. Ferrimagnetic resonance measurements show 18 Oe of linewidth (δH) at 9 GHz. The combination of low δH with a high δHA in Zr-ZnY hexaferrite is suitable for microwave devices, which can operate with low external biasing field. © 2011 American Institute of Physics. Source

Zhang Z.,CA Technologies | Liu K.,CA Technologies | Jin E.X.,CA Technologies | Dovek M.M.,CA Technologies | And 5 more authors.
IEEE Transactions on Magnetics | Year: 2016

Heat-assisted magnetic recording (HAMR) has become one of the leading approaches to increase the areal density in hard disk drives to several Tb/in2. Laser-induced protrusion significantly impacts the HAMR heads' performance and lifetime. Nonetheless, the pointy local protrusion amount is hard to accurately quantify by touchdown sensors. Based on the previous indirect thermal-mechanical studies with different sensors and techniques, a new methodology is developed to measure the laser-induced protrusion by burnishing the head during writing with laser powered ON and by utilizing atomic force microscopy scans. This burnish method requires the air-bearing surface (ABS) to physically contact the rotating disk without an excessive overdrive, which relies on the precise settings of the touchdown sensors and the detection methods. The time dependence of the burnish behavior is studied. The results show that its time constant is much longer than the pure thermal and mechanical time constants. The repeatability of the experiment is validated. The local protrusion induced by the laser is in the range of 2-5 nm based on current head design. Accordingly, the detailed studies about heater power effects and protrusion amount as a function of laser power have been conducted. In addition, the impact of varying degrees of stiffness of the ABS is discussed. © 1965-2012 IEEE. Source

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