Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session A16: Focus Session: Magnetic Nanostructures I |
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Sponsoring Units: DMP GMAG Chair: Guoxing Miao, Massachusetts Institute of Technology Room: D173 |
Monday, March 21, 2011 8:00AM - 8:12AM |
A16.00001: Cantilever torque magnetometry studies of the in-plane to out-of-plane transition in a single nickel magnetic nanorod Eric W. Moore, SangGap Lee, Steven A. Hickman, Jonilyn G. Longenecker, John A. Marohn Torque magnetometry, using attonewton-sensitivity cantilevers, is extremely sensitive to both the average magnetic moment and magnetization fluctuations within a small magnetic tip. Operating at $T = 4 \: \textrm{K}$ with such a system, we study in-plane to out-of-plane magnetization switching in a single, electron beam lithographically defined nickel nanorod, of radius $r \approx 50 \: \textrm{nm}$. Numerous, simultaneous, peaks are visible in cantilever frequency, dissipation and jitter as well as Barkhausen like steps. A analytic model is developed that achieves order of magnitude agreement with the frequency and dissipation peaks. [Preview Abstract] |
Monday, March 21, 2011 8:12AM - 8:24AM |
A16.00002: Interedge magnetic coupling in metal-terminated graphene nanoribbons Yan Wang, Chao Cao, Hai-Ping Cheng Graphene nanoribbons (GNRs) with armchair or zigzag edges, a novel organic material system produced by cutting graphene along two crystallographic directions, have recently attracted considerable attention in spintronics. GNR with zigzag edges is known to be magnetic with two spin-polarized edge states, which are ferromagnetically ordered but antiferromagnetically coupled to each other. Most of the previous studies focus ribbons with zigzag edges and hydrogen terminations. Here we present a first-principles study\footnote{Y. Wang, C. Cao, and H.-P. Cheng, Phys. Rev. B 82, 205429 (2010).} of zigzag and armchair GNRs terminated with 3\emph{d} transition-metals and noble metals. Specifically, we investigate the long-range interedge magnetic coupling as a function of the ribbon's width. We also show that the proposed hybrid metal-terminated GN\footnote{Y. Wang and H.-P. Cheng, submitted.}Rs can be excellent candidate for spintronic applications. [Preview Abstract] |
Monday, March 21, 2011 8:24AM - 8:36AM |
A16.00003: Magnetic Properties of Single Crystal Nickel Nanowires Jimmy Kan, Keith Chan, Erik Shipton, Eric Fullerton Toward the goal of understanding magnetism in confined dimensions, we have synthesized Nickel nanowires (NWs) by chemical vapor deposition and characterized their magnetic properties. By tuning chemical vapor deposition synthesis parameters, we can controllably synthesize a variety of morphologically dissimilar Ni products onto untreated amorphous SiO2$\vert \vert $Si substrates [1]. These structures include polycrystalline core-shell NWs, single-crystal cubes, in-plane wires, and vertically-oriented single crystal arrays. To probe the magnetic properties of individual NWs, we combined magneto-transport, XPEEM, and magnetic modeling. For polycrystalline NWs, the magnetic properties are dominated by shape anisotropy. However, for single-crystal NWs, there is a competition between the shape anisotropy along the (001) direction and magneto-crystalline anisotropy along the (111) direction. This gives rise to complex magnetic stripe domain patterns along the wires, interesting magneto-transport properties, and novel reversal modes not typically observed in magnetic wires. \\[4pt] [1] K.T. Chan, J.J. Kan, E.E. Fullerton, et al., ``Oriented Growth of Single-Crystal Ni Nanowires onto Amorphous SiO2,'' Nano Letters, Oct. 2010 [Preview Abstract] |
Monday, March 21, 2011 8:36AM - 8:48AM |
A16.00004: Tunable magnetism in nanomaterials and systems Wanlin Guo, Zhuhua Zhang Tunable magnetism in nanomaterials and systems are especially attractive and hold great promise for applications in nanoelectronics and spintronics. Here we show some of our recent findings along this direction. First, we present a novel magnetoelectric effect in graphene nanoribbons settled on silicon substrates whereby the ribbon edge magnetization can be tuned linearly by applied bias voltage (\textbf{\textit{Phys.Rev.Lett}}, \textbf{103}, 187204, 2009), and this effect is robust to material and geometry variations (\textbf{\textit{Phys.Rev.B}} 81, 155428, 2010). We also realize an electrical control of magnetism in ZnO ribbons (\textbf{\textit{ACS Nano}} \textbf{4}, 2124, 2010\textbf{)}$_{,}$ and even a tunable magnetic ordering in sandwich nanowires by changing charge states (\textbf{\textit{J.Am.Chem.Soc}}.\textbf{132}, 10215, 2010). Contrast to the zero-gap graphene, both hexagon-BN sheets and nanotubes are generally insulating. We provide two efficient recipes to narrow the wide gap of BN: applying external electric fields for nanoribbons and increasing tube curvature for nanotubes. Of more interesting is that ferromagnetic ordering is obtained in BN nanotubes by fluorination and it can be remarkably modulated by applying radial pressure (\textbf{\textit{J.Am.Chem.Soc}}.\textbf{131}, 6874, 2009). Our revealed control of magnetism in a wide range of nanomaterials may open up new vistas towards spintronics. [Preview Abstract] |
Monday, March 21, 2011 8:48AM - 9:00AM |
A16.00005: Magnetic Properties of Iron-added Titanium Oxide Nanotubes Eugen Panaitescu, Pegah Hosseinpour, Laura H. Lewis, Latika Menon Titanium oxide represents a promising candidate as the support material for dilute magnetic semiconductors (DMSs), especially in a nanostructured form. Titania nanotubes ordered arrays produced by anodization have been used in this study as the base material for the addition of a ferromagnetic component, iron in particular. Several routes such as titanium-iron films co-deposition before anodization, anodization in iron cations containing solutions, and post-anodization iron deposition have been used for the incorporation of iron into the titanium oxide nanotubes matrix. Samples morphology and structure was analyzed by electron microscopy, and by EDS and XRD spectroscopy. Subsequent magnetic measurements were performed on both amorphous and crystalline samples, and compared with references such as blank nanotubes and commercial anatase nanoparticles powder. [Preview Abstract] |
Monday, March 21, 2011 9:00AM - 9:12AM |
A16.00006: Synthesis and Characterization of CoFe nanowires Po-Ching Tsai, Yajing Zhang, Girija S. Chaubey, Narayan Poudyal , Chuanbing Rong, J. Ping Liu CoFe and CoNi nanocrystals with different size, shape and compositions were successfully synthesized via a non-catalyst chemical solution method. It was found that the structure and morphology of the nanocrystals with high aspect ratio can be controlled by varying parameters such as solvent amount, surfactant ratio, reducing agent and heating rate. The elongation of the nanowires can be adjusted by changing surfactant ratio and catalyst amount. It has also been observed that the growth mechanisms for CoFe and CoNi nanowires are different. Magnetic properties of the nanocrystals are size and shape dependent. By optimizing the synthesis conditions, nanowires with enhanced magnetization and coercivity can be obtained. [Preview Abstract] |
Monday, March 21, 2011 9:12AM - 9:48AM |
A16.00007: Focused electron beam induced deposition of magnetic nanostructures Invited Speaker: Nanopatterning strategies of magnetic materials normally rely on standard techniques such as electron-beam lithography using electron-sensitive resists. Focused electron beam induced deposition (FEBID) is currently being investigated as an alternative single-step route to produce functional magnetic nanostructures. Thus, Co-based [1] and Fe-based [2] precursors have been recently investigated for the growth of magnetic nanostructures by FEBID. In the present contribution, I will give an overview of the existing literature on magnetic nanostructures by FEBID and I will focus on the growth of Co nanostructures by FEBID using Co$_{2}$(CO)$_{8}$ as precursor gas. The Co content in the nanostructures can reach 95{\%} [3]. Magnetotransport experiments indicate that full metallic behaviour is displayed with relatively low residual resistivity and standard anisotropic magnetoresistance (0.8{\%}) [3]. The coercive field of nanowires with changing aspect ratio has been determined in nanowires with width down to 150 nm by means of Magneto-optical Kerr Effect [4] and the magnetization reversal has been imaged by means of Magnetic Force Microscopy, Scanning Transmission X-ray Microscopy as well as Lorentz Microscopy experiments. Nano-Hall probes have been grown with remarkable minimum detectable magnetic flux. Noticeably, it has been found that the domain-wall propagation field is lower than the domain-wall nucleation field in L-shaped nanowires, with potential applications in magnetic logic, sensing and storage [5]. The spin polarization of these Co nanodeposits has been determined through Andreev-Reflection experiments in ferromagnetic-superconducting nanocontacts and amounts to 35{\%} [6]. Recent results obtained in Fe-based nanostructures by FEBID using Fe$_{2}$(CO)$_{9}$ precursor will be also presented [7]. \\[4pt] [1] I. Utke et al., Appl. Phys. Lett. 80 (2002) 4792-4794 \\[0pt] [2] M. Takeguchi et al., Nanotechnology 16 (2005) 1321-1325 \\[0pt] [3] A. Fern\'{a}ndez-Pacheco et al, J. Phys. D: Appl. Phys. 42 (2009) 055005 \\[0pt] [4] A. Fern\'{a}ndez-Pacheco et al, Nanotechnology 20 (2009) 475704 \\[0pt] [5] A. Fern\'{a}ndez-Pacheco et al, Appl. Phys. Lett. 94 (2009) 192509 \\[0pt] [6] S. Sangiao et al, Solid State Communications, in press \\[0pt] [7] R. Lavrijsen et al, Nanotechnology, submitted [Preview Abstract] |
Monday, March 21, 2011 9:48AM - 10:00AM |
A16.00008: Memory effect in magnetic nanowire arrays Xiaoming Kou, Xin Fan, Randy Dumas, Qi Lu, Yaping Zhang, Hao Zhu, Xiaokai Zhang, Kai Liu, John Xiao A memory effect has been demonstrated in magnetic nanowire arrays. The magnetic nanowire array has the ability to record the maximum magnetic field that the array has been exposed to after the field has been turned off. The origin of the memory effect is the strong magnetic dipole interaction among the nanowires. Switching field distributions among nanowires was studied with a first order reversal curve technique to elucidate the discrepancy between the experimental result and the theoretical explanation. Based on the memory effect, a novel and extremely low cost EMP detection scheme is proposed. It has the potential to measure magnetic field pulses as high as a few hundred Oe without breaking down. [Preview Abstract] |
Monday, March 21, 2011 10:00AM - 10:12AM |
A16.00009: ABSTRACT WITHDRAWN |
Monday, March 21, 2011 10:12AM - 10:24AM |
A16.00010: Magnetic hyperthermia in frozen and liquid ferrofluids R. Regmi, A. Naik, J.S. Thakur, P.P. Vaishnava, G. Lawes We report magnetic hyperthermia in dextran coated Fe$_{3}$O$_{4}$ nanoparticles suspended in an aqueous solution over a temperature range from -40 $^{o}$C to +40 $^{o}$C to investigate heating mechanisms in the solid and liquid states. We used an alternating magnetic field of 70 Oe at frequency of 395 kHz to produce heating in the 12 nm Fe$_{3}$O$_{4 }$nanoparticles. We found that at the lowest and highest temperatures, ambient heat flow to or from the environment produced small but non negligible effects. After correcting for this ambient heat flow, we found an average magnetic heating of 4.7 W/g, 11.2 W/g, and 6.5 W/g in the solid, mixed solid-liquid, and liquid phases, respectively. These values in the solid and liquid phases are consistent for models for magnetic heating considering Neel heating only and Neel and Brownian heating together, respectively. [Preview Abstract] |
Monday, March 21, 2011 10:24AM - 10:36AM |
A16.00011: Characterization of iron oxide-dextran magnetic nanoparticle suspensions J. Shih, R. Bai, W. Chiou, R.M. Briber, J.A. Borchers, C.L. Dennis, C. Gruettner Magnetic nanoparticles, with structures from core-shell to nanocrystallites in a matrix, are candidates for use in biomedical applications. ``Superparamagnetic iron oxide'' (SPIO) nanoparticles are nanocrystallites of iron oxide in a dextran matrix, with sizes between 20nm and 250nm. Dynamic light scattering (DLS), transmission electron microscopy (TEM), atomic force microscopy (AFM), and hysteresis measurements were used for structural and magnetic characterization. Additionally, cryoquench-TEM was performed, allowing direct imaging without false aggregation from drying. The DLS-determined size of the particles is 250nm, but cryoquench-TEM yields a smaller size of 150nm. In addition, the particles are relatively well-dispersed, but dimers and trimers are observed. This corresponds with the evidence of weak interactions in magnetic hysteresis measurements. Further magnetic characterization will provide information on how the magnetic properties of these SPIO particles correlate with their size and structure. [Preview Abstract] |
Monday, March 21, 2011 10:36AM - 10:48AM |
A16.00012: Thermosensitive Nanostructured Media for imaging and Hyperthermia Cancer Treatment Karen Martirosyan Hyperthermia has been used for many years to treat a wide variety of tumors in patients. The most commonly applied method of hyperthermia is capacitive heating by using microwave. Magnetic fluids based on iron oxide (Fe3O4), stabilized by biocompatible surfactants are typically used as heating agent. However, significant limitations of using commercial available magnetic particles are non-selectivity and overheating of surrounding normal tissues. To improve the efficacy of hyperthermia treatment we intend to develop Curie temperature (Tc)-tuned nanostructured media having T2 relaxation response on MRI for selective and self-controlled hyperthermia cancer treatment. As an active part of this media we fabricated superparamagnetic, biocompatible and dextran coated ferrite nanoparticles Mg1+xTixFe2(1-x)O4 at 0.3$<$x$<$0.5 with low Curie temperature. To tune Tc we produced a large number of ferrites powders with x=0.05 by aqueous combustion synthesis. This process typically involves a reaction in a solution containing metal nitrates and different fuels, which are classified based on the type of reactive groups (e.g., amino, hydroxyl, carboxyl) connected to a hydrocarbon chain, such as glycine, hydrazine, or urea. Our experiments revealed that ferrite with formula Mg1.35Ti0.35Fe1.3O4 appears with Curie temperature within 46-50\r{ }C. [Preview Abstract] |
Monday, March 21, 2011 10:48AM - 11:00AM |
A16.00013: Magnetism of Au Nanoparticles on \textit{Sulfolubus Acidocaldarius} S-Layer Juan Bartolome, F. Bartolome, L.M. Garcia, A.I. Figueroa, T. Herrmannsdoerfer, R. Skrotzki, R. Schoenemann, J. Wosnitza, S. Selenska-Pobell, A. Geissler, T. Reitz, F. Wilhelm, A. Rogalev Au nanoparticles (NP) with diameters of a few nm have been synthesized on a protein S-layer of \textit{Sulfolobus Acidocaldarius} bacteria. SQUID magnetization (1.8 K $<$ T $<$ 300 K and 0 $<$ B $<$ 7 T) shows superparamagnetic behavior at low-T. Its origin lays at the Au NP's, as has been proven by Au L$_{2,3-}$edge XMCD spectroscopy, performed in the range 2.2$<$T$<$20 K and up to B$_{app}$=17 T. XMCD analysis yields a total magnetic moment per Au atom $\mu _{Au}$= 0.050(1) $\mu _{B}$, a particle average moment m$_{part }$= 2.3 $\mu _{B}$, Au orbital to spin moment ratio of m$_{L}$/m$_{S }$= 0.29, and Curie-like superparamagnetism. Au-S bonds are detected by S K-edge XAS measurements. Besides, EXAFS at the Au L$_{3}$-edge shows that the Au NP internal structure is fcc, and Au-S bonds are located at the particle surface. An increase of the hole charge carrier density in the Au 5d band due to electron transfer with the S-layer explains the Au magnetism. The observed magnetic moment per Au atom is 25 times larger than those previously found by XMCD in Au-thiol capped NPs. [Preview Abstract] |
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