Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Z37: Focus Session: Nanomagnetism -- Nanoparticles II |
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Sponsoring Units: DMP GMAG Chair: Ilya Krivorotov, University of California, Irvine Room: E147-E148 |
Friday, March 19, 2010 11:15AM - 11:27AM |
Z37.00001: Progress toward Synthesis and Characterization of Rare-Earth Nanoparticles Dulce G. Romero, Pei-Chun Ho, Saeed Attar, Dennis Margosan Magnetic nanoparticles exhibit interesting phenomena, such as enhanced magnetization and reduced magnetic ordering temperature (i.e. superparamagnetism), which has technical applications in industry, including magnetic storage, magnetic imaging, and magnetic refrigeration. We used the inverse micelle technique to synthesize Gd and Nd nanoparticles given its potential to control the cluster size, amount of aggregation, and prevent oxidation of the rare-earth elements. Gd and Nd were reduced by NaBH$_{4}$ from the chloride salt. The produced clusters were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The results from the XRD show that the majority of the peaks match those of the surfactant, DDAB. No peaks of Gd were observed due to excess surfactant or amorphous clusters. However, the results from the SEM and EDX indicate the presence of Gd and Nd in our clusters microscopically, and current synthesized samples contain impurities. We are using liquid-liquid extraction method to purify the sample, and the results will be discussed. [Preview Abstract] |
Friday, March 19, 2010 11:27AM - 11:39AM |
Z37.00002: Shape-dependency of magnetic properties of FePt nanostructures Samaresh Guchhait, D.A. Ferrer, H. Liu, F. Ferdousi, C. Corbett, S.K. Banerjee The fabrication and magnetic properties of size- and morphology- controlled magnetic nanostructures have attracted much interest owing to their potential application in ultrahigh density magnetic recording media. Chemically ordered binary alloy L10- FePt has emerged as an ideal candidate for information storage as result of its ultrahigh uniaxial magnetocrystalline anisotropy and good chemical stability. The role of shape anisotropy in the magnetization reversal of FePt nanostructures remains as a fundamental issue to be clarified for both scientific and technological purposes. We have used wet chemistry to fabricate nanocrystals of different shapes and measured their magnetic properties using a SQUID magnetometer. Spheres have an average diameter of 3 nm, while ellipsoids are of average dimension of 3.5 nm by 2.5 nm. Rods have average diameter of 2.5 nm and length of 50-70 nm. The magnetic properties of the as-grown nanocrystals were dramatically enhanced after annealing. One can engineer the Curie temperature and coercive field of the nanostructures by tuning their shapes. Preliminary theoretical simulations enable us to qualitatively explain the dissimilar magnetic properties of these colloids. [Preview Abstract] |
Friday, March 19, 2010 11:39AM - 11:51AM |
Z37.00003: Elemental Specific Study on FeCo-Au nanoparticles Nian Ji, Yunhao Xu, Jian-Ping Wang Core-shell type nanoparticles are a topic of interest due to its diverse magnetic properties such as coercivity enhancement\footnote{J. Nogu\'{e}s et al., Phys. Rep. 422, 65 (2005)} and exchange bias.\footnote{O. Iglesias, et al., J. Nanosci. Nanotechnol. 8, 2761 (2008)} At the core-shell interface, the orbital magnetism is expected to change due to the symmetry broken, which could be substantial on the overall magnetic performance in nanoparticle system given its large surface to volume ratio. Here we present elemental specific and chemical selective XMCD study on high magnetic moment FeCo-Au core-shell nanoparticles, which are synthesized from a one-step gas condensation sputtering method. It is found the orbital magnetic moment of Fe and Co response differently when both elements are subject to the same broken symmetry. The spin and orbital magnetic moment on Fe and Co are determined according to XMCD sum rule, respectively. Giant orbital magnetic moment is observed on Co L edge while no significant change is found on Fe case. This finding hints at the necessary modification of Slater-Pauling curve of systems in nanoscale, pointing at a new direction on searching high materials with high magnetic moment. [Preview Abstract] |
Friday, March 19, 2010 11:51AM - 12:27PM |
Z37.00004: Magnetic nano-structures for the manipulation of individual nano-scale particles in bio-compatible environments Invited Speaker: The manipulation of geometrically constrained magnetic domain walls (DWs) in nanoscale magnetic strips has attracted much interest recently, with proposals for prospective memory and logic devices. Here we demonstrate that the high controllability of the motion of geometrically constrained DWs allows for the manipulation of individual nanoparticles carrying proteins or cells in solution on a chip with the active control of position at the nanometer scale. Our approach exploits the fact that magnetic nanoparticles in suspension can be captured by a DW, whose position can be manipulated with nanometer scale accuracy in specifically designed magnetic nanowire structures. We hereby show that the precise control over DW nucleation, displacement, and annihilation processes in such nanostructures allows for the capture, transport and release of magnetic nanoparticles. Although this application of nano-magnetism to bio-technology and nanomedicine is still in its infancy, it already reveals its huge potential as one example of the synergetic combination of nano-physics, nano-chemistry and nano-biotechnology. [Preview Abstract] |
Friday, March 19, 2010 12:27PM - 12:39PM |
Z37.00005: Iron et al.: Incorporation of Manganese in the Crystal Lattice of Magnetosome Magnetite Tanya Prozorov, Teresa Perez-Gonzalez, Concepcion Jimenez-Lopez, Surya K. Mallapragada, Paul Howse, Dennis A. Bazylinski, Ruslan Prozorov Incorporation of foreign metal into the crystal matrix of the magnetotactic bacterial magnetite has been attempted worldwide. Recently, presence of small amounts of cobalt and manganese in magnetosome magnetite crystals in cultured and uncultured magnetotactic bacteria, respectively, was reported. Magnetization of the uncultured cells and their magnetosomes were not determined, while only marginal changes in the magnetic properties of the cultured cobalt-grown cells and their magnetosomes were observed, however no evidence of incorporation of these metals into the crystalline lattice was presented. We grew cells of a magnetotactic bacterium, \textit{Magnetospirillum gryphiswaldense }strain MSR-1, in the presence of manganese, ruthenium, zinc and vanadium, of which only manganese was incorporated within the magnetosome magnetite crystals. For the first time we demonstrate that the magnetic properties of magnetite crystals of magnetotactic bacteria can be significantly altered by the incorporation of metal ions, other than iron, in the crystal structure, as signaled by a major shift in the Verwey transition. [Preview Abstract] |
Friday, March 19, 2010 12:39PM - 12:51PM |
Z37.00006: Controlling Brownian motion of magnetic microspheres by magnetic wire traps A. Chen, G. Vieira, T. Henighan, A. Hauser, F. Yang, C. Jayaprakash, R. Sooryakumar Microspheres with embedded superparamagnetic particles are being widely used in biomedical research to selectively influence biological entities. As most of these applications are in fluid-based suspensions, random Brownian movements of the microspheres have important consequences on their targeted behavior. We demonstrate a technique based on microscale ferromagnetic wires patterned on a silicon platform, where when the external field (H) augments the domain-wall field from the designed wires, the microspheres in the fluid can be tightly confined (trapped) within an area remote from the wires. Upon weakening the trap by tuning H, the amplitude or range of the Brownian motion steadily increases until an abrupt onset of large random fluctuations is reached. These results, which demonstrate control on the random walk of fluid-borne magnetic microspheres through non-contact forces, are well reproduced through simulations. [Preview Abstract] |
Friday, March 19, 2010 12:51PM - 1:03PM |
Z37.00007: Magnetic Polymer Nanocomposites with Tunable Microwave Properties K. Stojak, S. Pal, H. Srikanth, S. Skidmore, C. Morales, J. Dewdney, J. Wang, T. Weller Due to the multifunctionality, polymer nanocomposites (PNCs) have potential applications for electromagnetic interference shielding, tunable electromagnetic devices and flexible electronics. We report on synthesis, magnetic and RF characterization of polymer films loaded with varying concentrations of Fe$_{3}$O$_{4}$ and CoFe$_{2}$O$_{4}$ nanoparticles. The nanoparticles (5 $\pm $ 1 nm) were synthesized by chemical co-precipitation. Structural properties were characterized by XRD and TEM. Nanoparticles were dispersed through a solution method in a low-loss microwave polymer from the Rogers Corporation. No aggregation was observed and particles remain well dispersed throughout the volume of the polymer matrix. Magnetic measurements using a Physical Property Measurement System revealed characteristic features of superparamagnetism at room temperature and blocking at low temperature. Microwave transmission/reflection studies on the PNCs were done using a microstrip resonator technique, and strong tunability in the microwave absorption was observed. [Preview Abstract] |
Friday, March 19, 2010 1:03PM - 1:15PM |
Z37.00008: Unique Separation of Core-Shell Nanoparticle Components using Resonant X-Ray Scattering Kathryn Krycka, Julie Borchers, Josep Nogues, German Salazar-Alvarez, Jordi Sort Nanoparticle-based devices, fluids, and biomedical applications are at the research forefront due to an unprecedented ability to control growth and uniformity. In particular, it is now possible to produce bulk quantities of monodisperse nanoparticles comprised of distinctive chemical layers. Characterizing these internal structures with conventional techniques such as TEM, however, remains a challenge. Here we demonstrate using Fe-oxide and Mn-oxide core-shell nanoparticles, that multiple-energy resonant small angle x-ray scattering (SAXS) can be effectively utilized to uniquely and unambiguously separate the scattering contributions from the Fe oxide and the Mn oxide regions without any \textit{a priori} knowledge of the internal structure. This technique reveals that the nanoparticles have a monodispersity less than 10{\%} and a total spherical radius of 4.3 nm that is divided into a distinctive Fe oxide core of radius 1.5 nm and a Mn oxide impregnated shell covering the outermost 2.8 nm. Although especially well suited for determining core-shell nanoparticle morphology, this novel approach is applicable for resolving the diffraction contributions from any layered system such as multilayered ultra-thin films. [Preview Abstract] |
Friday, March 19, 2010 1:15PM - 1:27PM |
Z37.00009: Soft Magnetic Nanocomposites Assembled by Fe/Al$_{2}$O$_{3}$ Core-Shell Nanoparticles with Tunable High-Frequency Property Q. Yao, J.A. Sundararajan, D.T. Zhang, H. Han, D. Meyer, Y. Qiang High-frequency soft magnetic films synthesized at room temperature (RT) are significant to the growing demand for improvement of next-generation microelectronic devices. For working in the gigahertz range, it is a challenge to develop uniaxial anisotropic films with high saturation magnetization, small coercivity and large resistivity. Accordingly, new Fe/Al$_{2}$O$_{3}$ core-shell cluster-assembled nanocomposites are created by employing novel energetic cluster impact. By applying potentials up to 20 kV to tilted Si substrates, in-plane uniaxial anisotropy is induced and tailored at RT, which is interpreted by the uniaxial shape anisotropy of the ellipsoidal nanoparticles and the alignment of the nanoparticle assembly. Moreover, the Fe/Al$_{2}$O$_{3}$ core-shell ratio is adjusted to control the excellent magnetic softness and ultra-high resistivity. Consequently, the Si-integration compatible nanocomposite films demonstrate tunable magnetic dynamic properties up to 8.5 GHz, measured by a shorted transmission-line perturbation method. [Preview Abstract] |
Friday, March 19, 2010 1:27PM - 1:39PM |
Z37.00010: Synthesis and Magnetic Properties of Cobalt Carbide Nanoparticles Yajing Zhang, Girija Chaubey, Chuanbing Rong, Narayan Poudyal, Po-ching Tsai, J. Ping Liu, Yong Ding Co-based alloys and compounds have wide applications in traditional and advanced materials. Co$_{n}$C (n=1-6) thin film and bulk materials have drawn much attention and been studied experimentally though less report can be found in studies of their magnetic properties. We report synthesis and characterization of cobalt carbide (Co$_{3}$C and Co$_{2}$C) nanoparticles by a one-pot polyol reduction process. Tetraethylene glycol was used as both the solvent and reducing agent, and polyvinylpyrrolidone (PVP) as the surfactant. It is found that the size, structure and magnetic properties of the product can be controlled by adjusting the reaction parameters, such as the heating rate, the concentration of NaOH and PVP. PVP plays an important role in controlling the particle size, and therefore magnetic properties. By changing the concentration of PVP, the particle size can be adjusted from 1 micrometer to 20 nm and the coercivity reaches to the maximum value of 3.2 kOe at room temperature when the size was reduced to 20 nm. Thermomagnetic measurements showed that the Curie temperature of the cobalt carbide nanoparticles is around 500 K. Decomposition of the carbides was observed at about 700 K at which the cobalt carbides decomposed into pure Co during measurement. [Preview Abstract] |
Friday, March 19, 2010 1:39PM - 1:51PM |
Z37.00011: Femtosecond functionalization of magnetic 2- and 3-center nanostructures Wolfgang H\"{u}bner, Sander Kersten, Chun Li, Georg Lefkidis We present an \emph{ab initio} theory of ultrafast nanologic elements based on optical $\Lambda$-processes [1]. Using high-level quantum chemistry we show that in 2- and 3-magnetic-center structures containing Fe, Co and Ni as active centers both spin flips and spin transfers are possible within a hundred femtoseconds. Spin transfer can be resolved by a sufficiently large shift of the vibrational stretch frequency of a CO marker [2]. From 3-magnetic-center clusters we are able to construct OR, XOR (CNOT), and AND gates [3]. Thus multicenter magnetic clusters allow to exploit spin dynamics for full-fledged logic functionalization.\\[4pt] [1] G. Lefkidis, G. P. Zhang, and W. H\"{u}bner, PRL (2009, in press)\\[0pt] [2] C. Li, T. Hartenstein, G. Lefkidis and W. H\"{u}bner {\bf 79}, 180413(R) (2009)\\[0pt] [3] W. H\"{u}bner, S. Kersten and G. Lefkidis PRB {\bf 79}, 184431 (2009) [Preview Abstract] |
Friday, March 19, 2010 1:51PM - 2:03PM |
Z37.00012: Surface Induced Magnetic Switching in Nanoparticles Nathan Horrel, Renat Sabirianov We show that the magnetic structure of nanoparticles with competing exchange interactions, i.e. having ferromagnetic exchange coupling between nearest neighbors, J01, and antiferromagnetic one between second nearest neighbors, J02, is very sensitive to the ratio of these exchanges, R=-J02/J01. The magnetic structurein ground state changes as a function of R from ferromagnetic to non-collinear, and to antiferromagnetic. This change occurs in a very narrow window of R. The moderate modification of the surface exchange parameters of such nanoparticle may lead to a substantial change in the temperature dependence of its total magnetic moment. Using Monte Carlo simulations we show that the ``ordering'' temperature of nanoparticles of 3-4nm in diameter can be varied by about 25{\%} with the change of nearest neighbor exchange by only 25{\%}. Thus, if the surface exchange is modified by the external stimuli in core shell nanoparticles, the magnetic moment of the nanoparticle can be switched from nearly zero to about half of its maximum value. We discuss the modification of surface exchange in core-shell nanoparticles with core of iron oxide and shell made of photochromic materials as azobenzene. [Preview Abstract] |
Friday, March 19, 2010 2:03PM - 2:15PM |
Z37.00013: Structural and Magnetic Properties of As-Prepared and Annealed Ni/Cu Core/Shell Nanoparticles Thomas Ekiert, Kyler Carroll, Everett Carpenter, Karl Unruh Air stable Ni-core Cu-shell nanoparticles with diameters between about 100 and 300 nm have been synthesized via a one-pot polyol synthesis. Structural and chemical analysis shows the particles to be essentially free of metallic oxides and copper rich (Cu$_{59}$Ni$_{41})$, while room temperature magnetic measurements indicate a similar composition. The freely-flowing powder was compacted into disks under moderate pressure and a series of these samples were were annealed by scanning in a DSC to progressively higher maximum temperatures under a constant flow of forming gas. A DSC scan to a maximum temperature of 250 \r{ }C results in a large drop in the coercivity (208 Oe to 133 Oe) and relatively little change in the high-field magnetization ($\sim $20 emu/g of sample) and XRD-determined lattice parameter (0.3625(1) nm to 0.36169(5) nm). The high-field (H=9T) magnetization remains relatively unchanged near 20 emu/g for samples similarly scanned up to 400 \r{ }C, while samples scanned to higher temperatures have high-field magnetizations and coercivities that drop to a final value of 2.8 emu/g and 76 Oe upon scanning to 600 \r{ }C. [Preview Abstract] |
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