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Full-Text Articles in Physics

Fourier Transform Infrared Spectroscopy And Wide-Angle X-Ray Scattering: Investigations On Polypropylene–Vapor-Grown Carbon Nanofiber Composites, Mircea Chipara, John Hamilton, Alin Cristian Chipara, Tom George, Dorina Magdalena Chipara, Elamin E. Ibrahim, Karen Lozano, David J. Sellmyer Jul 2012

Fourier Transform Infrared Spectroscopy And Wide-Angle X-Ray Scattering: Investigations On Polypropylene–Vapor-Grown Carbon Nanofiber Composites, Mircea Chipara, John Hamilton, Alin Cristian Chipara, Tom George, Dorina Magdalena Chipara, Elamin E. Ibrahim, Karen Lozano, David J. Sellmyer

David Sellmyer Publications

Fourier transform infrared (FTIR) spectroscopy and wide-angle X-ray scattering (WAXS) investigations of isotactic polypropylene (iPP)–vapor-grown carbon nanofiber (VGCNF) composites containing various amounts of VGCNFs ranging between 0 and 20 wt %. are reported. The FTIR investigations were focused on the regularity bands of iPP. The FTIR data indicated a drop in the isotac­ticity index as the concentration of nanofibers was increased; this suggested a decrease in the crystallinity. WAXS measurements revealed a dominating α1 phase, with a small admixture of γ phase or mesophase. The loading of the polymeric matrix with car­bon nanofibers (CNFs) did not induce ...


Ultrahard Magnetic Nanostructures, P. K. Sahota, Yi Liu, Ralph Skomski, Priyanka Manchanda, R. Zhang, M. Franchin, H. Fangohr, George C. Hadjipanayis, Arti Kashyap, David J. Sellmyer Jan 2012

Ultrahard Magnetic Nanostructures, P. K. Sahota, Yi Liu, Ralph Skomski, Priyanka Manchanda, R. Zhang, M. Franchin, H. Fangohr, George C. Hadjipanayis, Arti Kashyap, David J. Sellmyer

David Sellmyer Publications

The performance of hard-magnetic nanostructures is investigated by analyzing the size and geometry dependence of thin-film hysteresis loops. Compared to bulk magnets, weight and volume are much less important, but we find that the energy product remains the main figure of merit down to very small features sizes. However, hysteresis loops are much easier to control on small length scales, as epitomized by Fe-Co-Pt thin films with magnetizations of up to 1.78 T and coercivities of up to 2.52 T. Our numerical and analytical calculations show that the feature size and geometry have a big effect on the ...


Nanomagnetic Skyrmions, Ralph Skomski, Zhen Li, Rui Zhang, Roger D. Kirby, Axel Enders, Daniel Schmidt, Tino Hofmann, Eva Schubert, David J. Sellmyer Jan 2012

Nanomagnetic Skyrmions, Ralph Skomski, Zhen Li, Rui Zhang, Roger D. Kirby, Axel Enders, Daniel Schmidt, Tino Hofmann, Eva Schubert, David J. Sellmyer

David Sellmyer Publications

Magnetic skyrmions and other topologically protected nanostructures are investigated. Since skyrmions are mathematical rather than physical objects, they describe a wide variety of physical systems, from simple magnetic domain walls to complicated quantum phases with long-range many-body entanglement. Important distinctions concern the skyrmions’ relativistic character, their quantum-mechanical or classical nature, and the one- or many-body character of the wave functions. As specific examples we consider magnetic nanospirals, where the topology of a vortex-like spin state is protected by magnetostatic interactions, and edge currents in dilute magnetic semiconductors and metallic nanodots. Our analysis militates against giant orbital moments created by a ...


Structural And Magnetic Properties Of Mn2 +ΔTisn, Parashu Kharel, Yung Huh, Shah R. Valloppilly, Xingzhong Li, N. Al-Agtash, K. Tarawneh, E. S. Krage, Renat F. Sabirianov, Ralph Skomski, David J. Sellmyer Jan 2012

Structural And Magnetic Properties Of Mn2 +ΔTisn, Parashu Kharel, Yung Huh, Shah R. Valloppilly, Xingzhong Li, N. Al-Agtash, K. Tarawneh, E. S. Krage, Renat F. Sabirianov, Ralph Skomski, David J. Sellmyer

David Sellmyer Publications

The structural and magnetic properties of Mn2 +δTiSn prepared by arc melting and annealing have been investigated. Structural studies show that the compound crystallizes in the hexagonal Ni3Sn-type structure with a=5.70Å and c=4.55Å . The phase stability of Mn2TiSn in the hexagonal structure is supported by the first-principle electronic structure calculations where the total energy per unit-cell volume in the hexagonal structure is smaller than that in the cubic structure. Field and temperature dependence of magnetization show that the sample is magnetically ordered with a Curie temperature around 400 K. The ...


A Quantum-Mechanical Relaxation Model, Ralph Skomski, Arti Kashyap, David J. Sellmyer Jan 2012

A Quantum-Mechanical Relaxation Model, Ralph Skomski, Arti Kashyap, David J. Sellmyer

David Sellmyer Publications

The atomic origin of micromagnetic damping is investigated by developing and solving a quantum-mechanical relaxation model. A projection-operator technique is used to derive an analytical expression for the relaxation time as a function of the heat-bath and interaction parameters. The present findings are consistent with earlier research beyond the Landau-Lifshitz-Gilbert (LLG) equation and show that the underlying relaxation mechanism is very general. Zermelo’s recurrence paradox means that there is no true irreversibility in non-interacting nanoparticles, but the corresponding recurrence times are very long and can be ignored in many cases.


L10 Crpt Phase Formation And Magnetic Properties, Rui Zhang, Ralph Skomski, Xingzhong Li, Zhen Li, Priyanka Manchanda, Arti Kashyap, Roger D. Kirby, Sy-Hwang Liou, David J. Sellmyer Jan 2012

L10 Crpt Phase Formation And Magnetic Properties, Rui Zhang, Ralph Skomski, Xingzhong Li, Zhen Li, Priyanka Manchanda, Arti Kashyap, Roger D. Kirby, Sy-Hwang Liou, David J. Sellmyer

David Sellmyer Publications

L10-ordered antiferromagnetic CrPt is of interest as a pinning material in exchange-biased system due to its many intriguing properties and such alloy with a (001) texture has also been used to serve as an underlayer to promote the L10 phase formation of other materials. Therefore, it is important to control not only the L10 phase formation of such material but also the texture of its ordered phase. A systematic study of the L10 phase formation of CrPt thin film was performed. The anisotropy of CrPt L10 phase has also been investigated both experimentally using ...


Assembly Of Uniaxially Aligned Rare-Earth-Free Nanomagnets, Balamurugan Balamurugan, Bhaskar Das, Shah R. Valloppilly, Ralph Skomski, Xingzhong Li, David J. Sellmyer Jan 2012

Assembly Of Uniaxially Aligned Rare-Earth-Free Nanomagnets, Balamurugan Balamurugan, Bhaskar Das, Shah R. Valloppilly, Ralph Skomski, Xingzhong Li, David J. Sellmyer

David Sellmyer Publications

We report HfCo7 nanoparticles with appreciable permanent-magnet properties (magnetocrystalline anisotropy K1≈10 Mergs/cm3, coercivity Hc ≈ 4.4 kOe, and magnetic polarization Js≈10.9 kG at 300 K) deposited by a single-step cluster-deposition method. The direct crystalline-ordering of nanoparticles during the gas-aggregation process, without the requirement of a high-temperature thermal annealing, provides an unique opportunity to align their easy axes uniaxially by applying a magnetic field of about 5 kOe prior to deposition, and subsequently to fabricate exchange-coupled nanocomposites having Js as high as 16.6 kG by co-depositing soft magnetic Fe-Co. This ...


One-Step Fabrication Of L10 Fept Nanocubes And Rods By Cluster Beam Deposition, W Li, O Akdogan, George C. Hadjipanayis, Ralph Skomski, David J. Sellmyer Jan 2012

One-Step Fabrication Of L10 Fept Nanocubes And Rods By Cluster Beam Deposition, W Li, O Akdogan, George C. Hadjipanayis, Ralph Skomski, David J. Sellmyer

David Sellmyer Publications

In this work, single crystal L10 FePt nanocubes have been successfully produced by a cluster beam deposition technique without the need of post annealing. Particles have been deposited by dc magnetron sputtering using high Ar pressures on both single crystal Si substrates and Au grids for the measurement of magnetic and structural properties, respectively. The nanocubes have a uniform size distribution with an average size of 5nm. At 1 Torr, the particles have the L10 structure with an order parameter of 0.5 and a RT coercivity of 2 kOe with high switching fields observed in the hysteresis ...


Effects Of Deposition Temperature And In-Situ Annealing Time On Structure And Magnetic Properties Of (001) Orientation Fept Films, Yongsheng Yu, T A. George, Haibo Li, Daqian Sun, Zhenan Ren, David J. Sellmyer Jan 2012

Effects Of Deposition Temperature And In-Situ Annealing Time On Structure And Magnetic Properties Of (001) Orientation Fept Films, Yongsheng Yu, T A. George, Haibo Li, Daqian Sun, Zhenan Ren, David J. Sellmyer

David Sellmyer Publications

FePt films were prepared on (100) oriented single crystal MgO substrates at high temperature rang-ing from 620 until 800°C and in-situ annealed for different times ranging from 0 to 60 min to obtain ordered FePt films. The structural analysis indicates that FePt films grow epitaxially on MgO (100) substrates. Both increasing deposition temperature and in-situ annealing time enhance the (001) tex-ture and ordering of FePt films. The magnetic analysis shows that these L10 FePt films have perpen-dicular anisotropy and the easy magnetization c-axis is perpendicular to the film plane. Magnetization reversal is controlled by a rotational mechanism. The hard ...


Hysteresis And Relaxation In Granular Permanent Magnets, Ralph Skomski, Balamurugan Balamurugan, Thomas A. George, Mircea Chipara, Xiao-Hui Wei, Jeffrey E. Shield, David J. Sellmyer Jan 2012

Hysteresis And Relaxation In Granular Permanent Magnets, Ralph Skomski, Balamurugan Balamurugan, Thomas A. George, Mircea Chipara, Xiao-Hui Wei, Jeffrey E. Shield, David J. Sellmyer

David Sellmyer Publications

Some nontrivial aspects of the magnetic and structural characterization of hard-magnetic nanoparticles are investigated. Dilute ensembles are well-described by mean-field theory, although there is an asymmetry between exchange and magnetostatic interaction fields. Corrections to the mean-field approximation are caused by cooperative effects and have the character of Onsager reaction fields, which are much stronger in micromagnetism than in atomic-scale magnetism. The slow dynamics of zero-field-cooled (ZFC) magnetization curves is strongly affected by the particles0 magnetic anisotropy, which reduces the corresponding energy-barrier height from 25 to 19.1 kBT.


Magnetism Of Directly Ordered Sm-Co Clusters, Balamurugan Balasubramanian, Ralph Skomski, Xingzhong Li, George C. Hadjipanayis, David J. Sellmyer Jan 2012

Magnetism Of Directly Ordered Sm-Co Clusters, Balamurugan Balasubramanian, Ralph Skomski, Xingzhong Li, George C. Hadjipanayis, David J. Sellmyer

David Sellmyer Publications

Sm-Co bulk alloys have shown superior permanent-magnet properties, but research on Sm-Co nanoparticles is challenging because of the need to control particle size, size-distribution, crystalline ordering, and phase purity. In the present study, a cluster-deposition method was used to produce Sm-Co nanoparticles having desired crystal structures without the requirement of subsequent high-temperature thermal annealing. Poorly crystallized SmCo5 nanoparticles exhibit a low room-temperature coercivity of only 100 Oe, whereas crystalline SmCo5 and Sm2Co17 nanoparticles show room-temperature coercivities of 2000 and 750 Oe, respectively. The direct synthesis of Sm-Co nanoparticles having sizes of less than 10 nm ...


Structural, Magnetic, And Electron Transport Properties Of Mnbi:Fe Thin Films, Parashu Kharel, Xingzhong Li, Shah R. Valloppilly, Nabil M. Al-Aqtash, K. Tarawneh, Renat F. Sabirianov, Ralph Skomski, David J. Sellmyer Jan 2012

Structural, Magnetic, And Electron Transport Properties Of Mnbi:Fe Thin Films, Parashu Kharel, Xingzhong Li, Shah R. Valloppilly, Nabil M. Al-Aqtash, K. Tarawneh, Renat F. Sabirianov, Ralph Skomski, David J. Sellmyer

David Sellmyer Publications

The structural, magnetic, and electron transport properties of Mn55=xFexBi45 (x¼0, 2, 4, 5, 8, 11, 13, 16) films prepared by multilayer deposition and annealing using e-beam evaporation have been investigated. Fe doping has produced a significant change in the magnetic properties of the samples including the decrease in saturation magnetization and magnetocrystalline anisotropy and increase in coercivity. Although the magnetization shows a smooth decrease with increasing Fe concentration, the coercivity jumps abruptly from 8.5 kOe to 22 kOe as Fe content changes from 4% to 5%, but the change in coercivity is small as the concentration goes beyond ...


Magnetism Of Dilute Co(Hf) And Co(Pt) Nanoclusters, Balamurugan Balasubramanian, Ralph Skomski, Xingzhong Li, Shah R. V, Priyanka Manchanda, Arti Kashyap, David J. Sellmyer Jan 2012

Magnetism Of Dilute Co(Hf) And Co(Pt) Nanoclusters, Balamurugan Balasubramanian, Ralph Skomski, Xingzhong Li, Shah R. V, Priyanka Manchanda, Arti Kashyap, David J. Sellmyer

David Sellmyer Publications

An investigation of the magnetic properties of Co-rich nanoparticles alloyed with a small fraction of Pt and Hf is presented. Co(Hf) and Co(Pt) nanoparticles with less than 15 at% of dopants were produced using a cluster-deposition method. The nanoparticles have sizes of less than 10 nm and show improved magnetic properties upon doping. Maximum coercivities of 900 Oe (at 300 K) and 2000 Oe (at 10 K) were observed for Co nanoparticles alloyed with 14.1 at% of Hf. Doped nanoparticles also exhibit high anisotropies, such as K1¼9.98 Mergs=cm3 (14.1 at% of ...


Accessibility And Selective Stabilization Of The Principal Spin States Of Iron By Pyridyl Versus Phenolic Ketimines: Modulation Of The 6A1 ↔ 2T2 Ground-State Transformation Of The [Fen4O2]+ Chromophore, Musa S. Shongwe, Usama A. Al-Zaabi, Faizah Al-Mjeni, Carla S. Eribal, Imaddin A. Al-Omari, Hussein H. Hamdeh, Dariusz Matoga, Harry Adams, Michael J. Morris, Arnold L. Rheingold, Eckhard Bill, David J. Sellmyer Jan 2012

Accessibility And Selective Stabilization Of The Principal Spin States Of Iron By Pyridyl Versus Phenolic Ketimines: Modulation Of The 6A1 ↔ 2T2 Ground-State Transformation Of The [Fen4O2]+ Chromophore, Musa S. Shongwe, Usama A. Al-Zaabi, Faizah Al-Mjeni, Carla S. Eribal, Imaddin A. Al-Omari, Hussein H. Hamdeh, Dariusz Matoga, Harry Adams, Michael J. Morris, Arnold L. Rheingold, Eckhard Bill, David J. Sellmyer

David Sellmyer Publications

Several potentially tridentate pyridyl and phenolic Schiff bases (apRen and HhapRen, respectively) were derived from the condensation reactions of 2-acetylpyridine (ap) and 2′-hydroxyacetophenone (Hhap), respectively, with N-R-ethylenediamine (RNHCH2CH2NH2, Ren; R = H, Me or Et) and com-plexed in situ with iron(II) or iron(III), as dictated by the nature of the ligand donor set, to generate the six-coordinate iron compounds [FeII(apRen)2]X2 (R = H, Me; X– = ClO4–, BPh4–, PF6–) and [FeIII(hapRen)2]X (R = Me, Et; X– = ClO4–, BPh4–). Single-crystal X-ray analyses of [FeII(apRen ...


Structure And Magnetic Properties Of Co-W Clusters Produced By Inert Gas Condensation, Farhad Reza Golkar-Fard, Matthew J. Kramer, Y. Zhang, R. W. Mccallum, Ralph Skomski, David J. Sellmyer, Jeffrey E. Shield Jan 2012

Structure And Magnetic Properties Of Co-W Clusters Produced By Inert Gas Condensation, Farhad Reza Golkar-Fard, Matthew J. Kramer, Y. Zhang, R. W. Mccallum, Ralph Skomski, David J. Sellmyer, Jeffrey E. Shield

David Sellmyer Publications

In this article, inert-gas condensation was used to synthesize Co-W clusters. The formation, structure, and magnetic properties of the clusters were investigated. Sub-10-nm clusters were obtained, and the structures and average sizes were strongly dependent on sputtering power. At low sputtering powers, the clusters were predominantly amorphous, while, at high sputtering power, the clusters were crystalline. X ray diffraction and transmission electron microscopy revealed clusters with hcp structure at high sputtering power. The magnetic properties were dependent on the sputtering power and temperature, with the highest coercivity of 810 Oe at 10 K for high sputtering power.


Spin And Elastic Contributions To Isothermal Entropy Change, Tathagata Mukherjee, Ralph Skomski, Steven A. Michalski, David J. Sellmyer, Christian Binek Jan 2012

Spin And Elastic Contributions To Isothermal Entropy Change, Tathagata Mukherjee, Ralph Skomski, Steven A. Michalski, David J. Sellmyer, Christian Binek

David Sellmyer Publications

Statistical considerations of ensembles of localized magnetic moments reveal an upper bound of the isothermal entropy change when only the magnetic degrees of freedom are considered. In this case, the maximum molar isothermal entropy change is determined by the spin multiplicity and is equal to Rln(2J+1), where J is the angular momentum of an individual atom. However, in materials with giant magnetocaloric effect, the isothermal field-induced entropy change goes beyond the spin-multiplicity limit due to field-activated elastic degrees of freedom. Recently, we investigated a model of pairs of exchange-coupled Ising spins with variable real-space positions. We showed ...


Aligned And Exchange-Coupled L10 (Fe,Co)Pt-Based Magnetic Films, Yi Liu, Thomas A. George, Ralph Skomski, David J. Sellmyer Jan 2012

Aligned And Exchange-Coupled L10 (Fe,Co)Pt-Based Magnetic Films, Yi Liu, Thomas A. George, Ralph Skomski, David J. Sellmyer

David Sellmyer Publications

Films of aligned L10-structure (Fe,Co)Pt with fcc Fe(Co,Pt) are synthesized by co-sputtering Fe, Co, and Pt on an (001) MgO substrate with in situ heating at 830 degrees C. The nanostructures and magnetic properties of the films are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID). The compositions of the samples (Fe,Co)xPt1-x are designed to maintain an atomic Fe: Co ratio of 65: 35 while increasing the Fe,Co content in each successive sample. In samples with low Fe and Co concentration, the ...


Isothermal Entropy Changes In Nanocomposite Co:Ni67Cu33, Steven A. Michalski, Ralph Skomski, Xingzhong Li, Damien Le Roy, Tathagata Mukherjee, Christian Binek, David J. Sellmyer Jan 2012

Isothermal Entropy Changes In Nanocomposite Co:Ni67Cu33, Steven A. Michalski, Ralph Skomski, Xingzhong Li, Damien Le Roy, Tathagata Mukherjee, Christian Binek, David J. Sellmyer

David Sellmyer Publications

The temperature-dependent magnetic properties of artificial rare-earth, free-magnetic nanostructures are investigated for magnetic cooling. We consider two-phase nanocomposites, where 2 nm nanoclusters of cobalt are embedded in a Ni67Cu33 matrix. Several composite films were produced by cluster deposition. The average Co nanocluster size can be tuned by varying the deposition conditions. Isothermalmagnetization curves weremeasured at various temperatures 150K