Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session H22: Focus Session: Nanoparticles and Nanocomposites |
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Sponsoring Units: GMAG DMP Chair: Meigan Aronson, University of Michigan Room: Baltimore Convention Center 319 |
Tuesday, March 14, 2006 11:15AM - 11:27AM |
H22.00001: Magnetocaloric Effect in Nanoparticle Systems and Clathrates D.J. Rebar, J. Gass, S. Srinath, H. Srikanth, G.S. Nolas We report the magnetocaloric effect (MCE) in cobalt ferrite, manganese ferrite, and nickel ferrite nanoparticle systems and also the first observation of a large MCE in Eu$_{8}$Ga$_{16}$Ge$_{30}$ clathrate compounds. The ferrite nanoparticles were synthesized using organometallic precursors in a wet chemical technique and characterized by XPS and XRD. Change in entropy ($\Delta $S$^{mag})$ was calculated using the Maxwell relation from the family of M-H curves at different temperatures. The maximum entropy change in these nanoparticle systems is influenced by the particle size, overall distribution in anisotropy, and moments. Even though the entropy change for these nanoparticles is reasonably large in comparison to previous reports, it is much smaller in comparison to the bulk systems exhibiting giant MCE. We also investigated MCE in a bulk clathrate system and observed large entropy changes of 6 and 9.3 J/kg-K for the Type I and Type VIII clathrate phases, respectively. These results indicate that the clathrates known to possess excellent thermoelectric properties are also promising candidates as magnetic refrigerant materials. HS acknowledges support from NSF grant CTS-0408933 [Preview Abstract] |
Tuesday, March 14, 2006 11:27AM - 11:39AM |
H22.00002: Magnetotransport properties and microwave experiments on Co nanoparticles embedded in a Ag matrix Neus Domingo, Joan Manel Hern\'{a}ndez, Antonio Fern\'{a}ndez, Alberto Maria Testa, Chris Binns, Dino Fiorani, Javier Tejada The magnetic and magnetotransport properties of Co nanoparticles (1.6 nm diameter) embedded in Ag matrix with different volume fraction have been investigated. Magnetic measurements give evidence of blocking temperatures T$_{B}$ = 10 K (1.5{\%} volume fraction) and T$_{b}$ = 15 K (9.8 {\%} volume fraction). Such values, quite high for so small particle sizes, reveal an important surface contribution to the total anisotropy energy. From magnetoresistance measurements we have obtained typical values of GMR of the order of 10 {\%}. The data were analyzed with respect to the relationship $\Delta $R / R $\sim $ [M(H)]$^{\wedge 2}$. Then we have also studied the response of the samples with microwave radiation measuring the absorption properties of these nanoparticles as a function of the applied magnetic field at different temperatures. The relationship between magnetic and transport measurements is discussed. [Preview Abstract] |
Tuesday, March 14, 2006 11:39AM - 11:51AM |
H22.00003: Examination of Giant Magnetoresistance in Cu-Co Granular Films with Two-Particle Size Distribution Jian-Qing Wang, Nam Kim, Jordan Peck Giant Magnetoresistance (GMR) effect and magnetization curves above the blocking temperature were studied for Cu80Co20 granular thin films. The attempt was to understand the relationship between the GMR effect, magnetization, and the degree of interface contribution to the spin-dependent scattering in a unified scheme. When the magnetization curve is fitted to the Langevin function using an averaged single particle size, the average size of the estimated Co particles is 2.8 nm.1 However, when the magnetization curve is used to fit the GMR curve, there is a lack of agreement between the experimental data and the fitting. The discrepancies were resolved by assuming that there are two size distributions in the Co nano-particle population. Under such assumptions, good fittings can be achieved with the experimental curves for both the GMR and the magnetization, using the same set of parameters. The obtained average particle sizes for the smaller and the larger particles, and their respective populations, are 1.1 nm and 2.7 nm, and 0.35 and 0.65, respectively. The smaller particles are responsible for the high field GMR effect while the large ones are for the low field. The study has revealed that a certain degree of magnetic bulk scattering is present in the spin-dependent scattering in this system. 1. L.M. Malkinski, J.-Q. Wang, et al, Appl. Phys. Lett. 75, 844 (1999). [Preview Abstract] |
Tuesday, March 14, 2006 11:51AM - 12:03PM |
H22.00004: Understanding the Role of Oxygen in CoFeO$_{x}$ Superparamagnetic Nanoparticles Pamela Jeppson, Tony Caruso, Doug Schulz, Rob Sailer There is a present need for materials which provide both magnetic flux isolation and concentration. The primary application of such materials regards coatings for very sensitive (picotesla) magnetic field measurement or applied magnetic fields. The coatings help reduce 1/f noise and provide a means of controlling wanted or unwanted, internal and/or external magnetic fields. For the high permeability superparamagnetic materials that are presently in use, severe thin film limitations are keeping picotesla resolution from being realized. An example of such present limitations is the strain encountered in thin permalloy films. Beyond strain, there is also brittleness which impedes many inorganic, metallic films. The original goal of this research was to develop flexible and insulating superparamagnetic materials to help fulfill the present thin film limitations and to provide new applications, which utilize the insulating and/or flexible nature of the composite films. However, after optimizing the magnetic properties, we found an extreme saturation moment for some parameters of the transition metal oxide based films. The extreme saturation moments are attributed to the oxygen ratio and termination at the surface of the nanoparticle. This talk will focus on the surface magnetic structure and how it can enhance or suppress the soft properties of transition metal based oxide superparamagnetic nanoparticles. . [Preview Abstract] |
Tuesday, March 14, 2006 12:03PM - 12:15PM |
H22.00005: Magnetic Properties of Fe-alloy Catalyst Nanoparticles for Carbon Nanofiber Synthesis K. D. Sorge, Th. Leventouri, C. Finkel, O. Malkina, P. D. Rack, A. V. Melechko, J. D. Fowlkes, K. L. Klein, M. L. Simpson The magnetic properties of Fe-alloy nanoparticles, used as catalysts in vertically-aligned carbon nanofiber (VACNF) growth, has been investigated. First, Fe and Co or Ni were co-sputtered onto Si substrates in order to make a catalyst alloy film. These substrates were then placed in a plasma-enhanced CVD chamber with a substrate temperature of 700$^{\circ}$C and a flowing mixture of acetylene (C$_2$H$_2$) and ammonia (NH$_3$) gas. During the PECVD, the catalyst film breaks into nanoparticles of 50--200~nm and VACNFs are grown. EDX shows that the catalyst nanoparticles nominally have the deposited alloy ratio. In addition, the nanoparticles are still magnetic and have a non-negligible remanence and hysteresis. Their magnetic properties are investigated by SQUID magnetometry in applied field of $|H| \le 50$~kOe and temperatures of 5--400~K. In addition, AC susceptibility studies give energy loss characteristics of the co-synthesized VACNF system. [Preview Abstract] |
Tuesday, March 14, 2006 12:15PM - 12:27PM |
H22.00006: Size Effects in Nanostructured MnBi Laura H. Lewis, Kyongha Kang, Arnold Moodenba In addition to variations in temperature, pressure and magnetic field, nanostructuring can tailor the magnetostructural transition; in particular, transition temperatures and anisotropies may change as the material expresses large surface:volume ratios. Compositions near the Mn-Bi eutectic (Mn5Bi95, Mn10Bi90) were rapidly solidified to produce the ferromagnetic low-temperature phase (LTP) NiAs-type MnBi embedded in a Bi matrix. High-resolution TEM reveals that the two compositions have different microstructures: the Mn5Bi95 composition consists of isolated nanorods (10 nm $x$ 30 nm) self-assembled along the major hexagonal symmetry directions of the Bi matrix. In contrast, the Mn10Bi90 composition exhibits regions of equiaxed clustered MnBi precipitates (50 – 100 nm) in addition to regions of isolated nanorods. SQUID magnetometry shows that the Mn5Bi95 composition has an abrupt magnetization decrease for T $>$ 520 K associated with a first- order hysteretic magnetostructural transformation from LTP MnBi to high-temperature phase (HTP) MnBi. This transition temperature is 100 degrees lower than that of the Mn5Bi95 composition, which exhibits the bulk MnBi transition temperature of 633 K with second-order character. [Preview Abstract] |
Tuesday, March 14, 2006 12:27PM - 1:03PM |
H22.00007: Phase and Heterostructure Controlled Fabrication of Freestanding Magnetic Nanocrystals Invited Speaker: Magnetism at the nanoscale is still not fully understood. One of the major issues involved is the lack of precise experimental results. For nanoparticles, as their size shrinks the importance of surface atoms increases to such a level that they may dominate the overall magnetic performance. Clean and well defined surfaces on nanocrystals are therefore desirable to understand the surface effect with sufficient accuracy. Unfortunately, conventional fabrication techniques usually require specific surfactants or surface passivation agents, which may conceal the role of surface atoms. Here we report a unique technique that can prepare freestanding nanocrystals with controlled crystalline phase as well as desirous heterostructures. As an example, uniform L1$_{0}$ FePt nanoparticles with room temperature coercivity of 8.25 kOe were achieved. HRTEM analysis shows that these particles have perfect octahedron shape with only {\{}111{\}} surfaces exposed UHV compatible gas phase aggregation technique was used for the generation of nanoparticles. Atoms were generated from metal targets by using a magnetron sputtering gun, in which the plasma can be manipulated to provide certain circumstances for particle nucleation and growth. The materials were carried on by carrier gas from source to substrate so the nucleation and growth stages were separated in space. Monodispersity is therefore achieved together with controlled phase and structure. [Preview Abstract] |
Tuesday, March 14, 2006 1:03PM - 1:15PM |
H22.00008: Synthesis and characterization of functional magnetic nanocomposites J. Gass, J. Sanders, S. Srinath, H. Srikanth Magnetic nanoparticles and carbon nanotubes have been excellent functional materials that could be dispersed in polymer matrices for various applications. However, uniform dispersion of particles in polymers without agglomeration is quite challenging. We have fabricated PMMA/polypyrrole bilayer structures embedded with Fe$_{3}$O$_{4}$ magnetite nanoparticles synthesized using wet chemical synthesis. Agglomeration-free dispersion of nanoparticles was achieved by coating the particles with surfactants and by dissolving both the particles and PMMA in chlorobenzene. Structural characterization was done using XRD and TEM. Magnetic properties of the bilayer structures indicated superparamagnetic behavior that is desirable for RF applications as the magnetic losses are reduced. Our polymer nanocomposite bilayer films with conducting polymer coatings are potential candidates for tunable RF applications with integrated EMI suppression. We will also report on our studies of pumped ferrofluids flowing past carbon nanotubes that are arranged in microchannel arrays. Magnetization under various flow conditions is investigated and correlated with the hydrodynamic properties. This scheme provides a novel method of energy conversion and storage using nanocomposite materials. [Preview Abstract] |
Tuesday, March 14, 2006 1:15PM - 1:27PM |
H22.00009: Iron nanoparticles embedded in SrTiO$_{3}$ via ion implantation1 P.V. Wadekar, Q.Y. Chen, X.M. Wang, H.W. Seo, O. Lozano, D.H. Kim, Z.H. Zhang, J.R. Liu, Y.Y. Xue, Wei-Kan Chu Magnetic nanoparticles are interesting because of their possible applications ranging from biomedicine to data storage. Syntheses of iron nanoparticles embedded in YSZ and Al$_{2}$O$_{3}$ matrices by ion implantation have already been reported in literature. It is thus natural to ask if SrTiO$_{3}$ would be a good alternative matrix material because of its compatibility with silicon and the unique dielectric behaviors. In this work, 60 keV Fe$^{+}$ ions were implanted at room temperature into single-crystalline substrates of SrTiO$_{3}$ to a dosage of 5x10$^{16}$ ions/cm$^{2}$. The specimens were then annealed at different temperatures in various ambient to bring about the nano-precipitation. Spectrophotometry, SQUID magnetometry, X-ray diffraction, electron microscopy, and electrical measurements were conducted to understand the magnetic and electrical properties in relation to the structures of the nano-composites formed under various conditions of ion implantation and post-annealing. [Preview Abstract] |
Tuesday, March 14, 2006 1:27PM - 1:39PM |
H22.00010: $^{1}$H NMR Spectra vs. the Bulk Magnetization of Magnetically Heterogeneous Systems with Nano- and Micro-scale Magnetic Inclusions E.M. Levin, A. Rawal, S.L. Bud'ko, K. Schmidt-Rohr The bulk magnetization of magnetically heterogeneous systems, where magnetic nano- and micro-particles are dispersed in a diamagnetic matrix, is correlated with their $^{1}$H static and magic angle spinning (MAS) NMR spectra. Mixtures containing magnetic Fe$_{2}$O$_{3}$ nano- and micro-particles varying from 0.5 to 8 mass {\%} in a matrix of diamagnetic laponite layered silicate were studied as model systems. Laponite has two characteristic centerbands in $^{1}$H NMR, which allow us to exclude contributions that can arise from protons possibly associated with the iron oxide particles. An increase in the concentration of magnetic particles results in an increase of the width of static $^{1}$H NMR spectra. In contrast, all $^{1}$H MAS spectra show a very narrow centerband and a clear sideband pattern, which is due to magnetic dipole-dipole interactions and depends on the concentration of the Fe$_{2}$O$_{3}$ particles. Unexpectedly, $^{1}$H MAS NMR spectra are observed even if the materials have a very large magnetization of 4.8 emu/g. The width of the NMR signal increases linearly with the total bulk magnetization, which can be explained by a scaling model. [Preview Abstract] |
Tuesday, March 14, 2006 1:39PM - 1:51PM |
H22.00011: Defect Induced Magnetism in Carbon Nanostructures S. Talapatra, T. Kim, R. Vajtai, S. Kar, Ji Yu Chen, M. Shima, P. Ajayan, M. Huang, D. Srivastava We report on the effect of nitrogen (N) and carbon (C) implantations on the magnetic properties of nanosized diamond particles, which show ferromagnetic hysteresis behavior at room temperature. The saturation magnetization in the N-implanted samples exceeds that of the C-implanted samples for dose sizes greater than 10$^{14}$/cm$^{2}$. The observed enhanced ferromagnetic ordering in N doped samples is explained on the basis of the structural modification (defects) and C-N bonding states, as investigated by high resolution transmission electron microscopy, Raman Spectroscopy and X-Ray Photo Electron Spectroscopy (XPS). [Preview Abstract] |
Tuesday, March 14, 2006 1:51PM - 2:03PM |
H22.00012: Magnetic Properties of Hetrostructured Layered Thin Films Based on Prussian Blue Derivatives$^{1}$ J.-H. Park, M.W. Meisel, F. Frye, D. R. Talham By utilizing a sequential deposition method and controlling the chemical composition of each layer, a series of hetrostructured layered thin films of different Prussian blue derivatives were fabricated. As a starting material, a thin film of 20 cycles of sequentially deposited Rb$_{j}$Ni$_{k}$[Cr(CN)$_{6}$]$_{l}$$\cdot$$n$H$_{2}$O film was generated, and the magnetization studies showed a ferromagnetic ordering at \emph{T}$_{C}$ $\sim$ 84 K and a frequency dependent susceptibility. A similar film of Rb$_{j}$Co$_{k}$[Fe(CN)$_{6}$]$_{l}$$\cdot$$n$H$_{2}$O is known to show anisotropic photoinduced magnetism.$^{2}$ A hetrostructured film was also prepared with Rb$_{j}$Ni$_{k}$[Cr(CN)$_{6}$]$_{l}$$\cdot$$n$H$_{2}$O and Rb$_{j}$Co$_{k}$[Fe(CN)$_{6}$]$_{l}$$\cdot$$n$H$_{2}$O alternately deposited for 10 cycles. The preliminary magnetooptical study of the hetrostructured film shows the presence of magnetic interactions between the layers of the two different Prussian blue derivatives. \linebreak\linebreak $^{1}$This work was supported, in part, by the National Science Foundation DMR-0305371 (MWM) and NSF DMR-0543362 (DRT). \linebreak $^{2}$J.-H. Park, E. \v{C}i\v{z}m\'{a}r, M. W. Meisel, Y. D. Huh, F. Frye, S. Lane, and D. R. Talham, Appl. Phys. Lett. 85, 3797 (2004). [Preview Abstract] |
Tuesday, March 14, 2006 2:03PM - 2:15PM |
H22.00013: Photoinduced Magnetism in Nanoparticles of Prussian Blue Derivatives N. E. Anderson, J.-H. Park, M. W. Meisel, F. Frye, D. R. Talham Nanoparticles of the Prussian blue family are of great interest due to the possibility for applications in magnetic memory, biosensing, and magnetic filtering. Nanoparticles also serve to better investigate fascinating phenomena, such as the anisotropic photomagnetic properties seen in thin films of Prussian blue derivatives.\footnote{J.-H. Park, E. {C}i\v{z}m\'{a}r, M. W. Meisel, Y. D. Huh, F. Frye, S. Lane, and D. R. Talham, Appl. Phys. Lett. \textbf{85}, 3797 (2004).} Here, we present results on Rb$_{j}$Co$_{k}$[Fe(CN)$_{6}$]$_{l}$$\cdot$$n$H$_{2}$O Prussian blue analog nanoparticles, which exhibit photoinduced magnetism. The nanoparticles are synthesized in a controlled manner, which allows for particle growth in the range of 5-50~nm. Early experiments show that upon irradiation with light at 5~K for a period of 2 hours, the final magnetization increases on the order of 10-100$\%$ compared to the initial dark state value. This increase is comparable in magnitude with the results reported for bulk materials. The change in magnetization is also accompanied by an increase in T$_{c}$. Furthermore, the effect of the dispersing agent on the photomagnetism, the size effect on characteristic magnetic properties, and ac susceptibility data will be presented. [Preview Abstract] |
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