Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 17 of 17
Full-Text Articles in Physics
Effects Of Germanium On The Electronic Transport Mechanism In Co20 (Cu-XGeX)80 Nanogranular Ribbons, J. He, Z. D. Zhang, J. Ping Liu, David J. Sellmyer
Effects Of Germanium On The Electronic Transport Mechanism In Co20 (Cu-XGeX)80 Nanogranular Ribbons, J. He, Z. D. Zhang, J. Ping Liu, David J. Sellmyer
David Sellmyer Publications
The dependency of giant magnetoresistance (GMR) on the nonmagnetic matrix in nanogranular Co20 (Cu1-xGex)80 ribbons was studied. When the matrix Cu is substituted with semiconductor Ge, the magnetoresistance transitioned from negative to positive at low temperatures. The positive GMR effect is closely related to the quantity of Co/Co3Ge2/Co junctionlike configurations. This result provides evidence for the competition between two types of electronic transport mechanisms in the magnetic granular ribbons: (i) electronic spin-dependent scattering, inducing a negative magnetoresistance and (ii) Coulomb blockade of the electronic tunneling, inducing a positive magnetoresistance.
Curie Temperature Of Fept:B2O3 Nanocomposite Films, H. Zeng, Renat F. Sabirianov, O. Mryasov, M.L. Yan, K. Cho, David J. Sellmyer
Curie Temperature Of Fept:B2O3 Nanocomposite Films, H. Zeng, Renat F. Sabirianov, O. Mryasov, M.L. Yan, K. Cho, David J. Sellmyer
David Sellmyer Publications
We report results on experimental and theoretical studies of structural and magnetic properties of FePt: B2O3 nanocomposite films. It was found for films prepared by magnetron sputtering with subsequent annealing that lattice parameters a and c of fct FePt change with significantly different rates with increase of the B2O3 fraction. As a consequence, fundamental magnetic properties change markedly, with the Curie temperature decreasing by 36% for 25% FePt volume fraction compared with the bulk value. Using an ab initio parametrization of magnetic interactions, we propose statistical model of thermal fluctuations in fct FePt, which …
Effect Of Grain Growth Inhibitors On The Hysteresis Properties Of Nd10Fe82C6B2Melt-Spun Alloys, M. Daniil, Y. Zhang, H. Okumura, George C. Hadjipanayis, David J. Sellmyer
Effect Of Grain Growth Inhibitors On The Hysteresis Properties Of Nd10Fe82C6B2Melt-Spun Alloys, M. Daniil, Y. Zhang, H. Okumura, George C. Hadjipanayis, David J. Sellmyer
David Sellmyer Publications
An effort has been made to improve the coercivity of nanocomposite Nd10Fe82C6B2 alloys, using small amounts (up to 1 at%) of Cr, Ti, Nb, Zr, and Ga. X-ray studies revealed that the amount of –Fe phase in both as-spun and annealed ribbons was significantly reduced for Nb and Zr substitutions, but increased for all the other substitutions. From the magnetic properties point of view, Zr (1 at%) was proven to be the most advantageous of all, since it increased the coercivity of annealed ribbons from 3.2 to 4.8 kOe and the maximum energy …
Permanent-Magnet Properties Of Thermally Processed Fept And Fept–Fe Multilayer Films, Jian Zhou, Ralph Skomski, Xingzhong Li, Wei Tang, George C. Hadjipanayis, David J. Sellmyer
Permanent-Magnet Properties Of Thermally Processed Fept And Fept–Fe Multilayer Films, Jian Zhou, Ralph Skomski, Xingzhong Li, Wei Tang, George C. Hadjipanayis, David J. Sellmyer
David Sellmyer Publications
FePt single-layer and FePt–Fe multilayer thin films are prepared by magnetron sputtering. By varying the Pt content, FePt, Fe3Pt, or a mixture of FePt and Fe3Pt can be obtained in Fe–Pt single layers. In annealed FePt–Fe multilayers, the coercivities decrease with the introduction of Fe layers compared to FePt single layers, while the magnetization increases. The single-phase behavior of the hysteresis loops of FePt–Fe multilayers indicates the existence of exchange coupling in these materials. For one FePt–Fe sample with optimized exchange coupling, the intrinsic properties correspond to an energy product of 19 MGOe. The texture of …
Magnetism Of Co Nanocluster Films, Y. Qiang, R.F. Sabiryanov, Sitaram Jaswal, Yi Liu, H. Haberland, David J. Sellmyer
Magnetism Of Co Nanocluster Films, Y. Qiang, R.F. Sabiryanov, Sitaram Jaswal, Yi Liu, H. Haberland, David J. Sellmyer
David Sellmyer Publications
A cluster-beam technique is used to produce nearly monodispersed nanoclusters of Co while independently varying their size and concentration. The Co clusters are embedded in Cu and SiO2 to form films with cluster size varying from 300 to 9000 atoms and Co concentration varying from 10 to 50 vol %. The Co magnetization (Ms) increases with increasing cluster size and decreases with increasing Co concentration for a given cluster size but is always less than the bulk value. First-principles calculations are used to analyze the experimental data in terms of the local environment effects at the …
Mechanically Milled Nanostructured (Sm,Pr) 12.5Co85.5Zr2 Magnets With Tbcu7 Structure, Hong Tang, Jian Zhou, David J. Sellmyer
Mechanically Milled Nanostructured (Sm,Pr) 12.5Co85.5Zr2 Magnets With Tbcu7 Structure, Hong Tang, Jian Zhou, David J. Sellmyer
David Sellmyer Publications
Nanostructured (Sm,Pr)(Co,Zr) magnets with the TbCu7-type structure have been synthesized by mechanically milling (Sm1-xPrx)12.5Co85.5Zr2 alloys (0≤x≤0.8) followed by appropriate annealing. Magnetic properties, structure, and microstructure have been investigated. It is found that single-phase (Sm,Pr)(Co,Zr) 7 magnets with the TbCu7 structure and with nanoscale grain size (14–19 nm) form in the whole composition range. Intrinsic coercivity Hci decreases from 20.7 to 5.6 kOe with increasing Pr content from 0 to 0.8, while energy products (BH)max shows an optimum value of 12.6 MGOe (Hciof 17.9 kOe) at …
Structure And Magnetic Properties Of Sputtered (Nd,Dy)(Fe,Co,Nb,B) 5.5/M (M = Feco,Co) Multilayer Magnets, W. Liu, Z.D. Zhang, J. Ping Liu, Xingzhong Li, X.K. Sun, David J. Sellmyer
Structure And Magnetic Properties Of Sputtered (Nd,Dy)(Fe,Co,Nb,B) 5.5/M (M = Feco,Co) Multilayer Magnets, W. Liu, Z.D. Zhang, J. Ping Liu, Xingzhong Li, X.K. Sun, David J. Sellmyer
David Sellmyer Publications
The magnetic properties of nanocomposite multilayer magnets of the (Nd,Dy)(Fe,Co,Nb,B) 5.5/M (M = Co,FeCo) on Ti-buffered Si substrates have been investigated. X-ray diffraction results reveal that the Nd2Fe14B-type phase in almost all the films is randomly oriented. Different thickness x (nm) for Co layers and y (nm) for FeCo layers were adopted in the multilayers. It is found that high remanence is achieved in the nanocomposite multilayer films consisting of the Nd2Fe14B-type phase and soft magnetic phase for Co with 6≥x≥4 and for FeCo with 10≥y≥6. The …
L10,(001)-Oriented Fept:B2O3 Composite Films For Perpendicular Recording, M.L. Yan, H. Zeng, Nathan D. Powers, David J. Sellmyer
L10,(001)-Oriented Fept:B2O3 Composite Films For Perpendicular Recording, M.L. Yan, H. Zeng, Nathan D. Powers, David J. Sellmyer
David Sellmyer Publications
A multilayered deposition structure was developed for fabricating FePt:B2O3 films. We successfully obtained nanostructured FePt:B2O3 films with FePt grains aligned perpendicular to film plane by postannealing the as-deposited multilayers at 550 °C for 30 min. It was found that development of (001) texture depends strongly on the total film thickness, initial B2O3 layer thickness, and Fe concentration. Nearly perfect (001) orientation of FePt-ordered grains can be obtained in the films with small total film thickness, large initial B2O3 layer thickness, and slightly higher Fe concentration. Our results show …
Magnetic Force Microscopy Observations Of The Magnetic Behavior In Co–C Nanodot Arrays, L. Gao, Sy_Hwang Liou, M. Zheng, Ralph Skomski, M.L. Yan, David J. Sellmyer, N.I. Polushkin
Magnetic Force Microscopy Observations Of The Magnetic Behavior In Co–C Nanodot Arrays, L. Gao, Sy_Hwang Liou, M. Zheng, Ralph Skomski, M.L. Yan, David J. Sellmyer, N.I. Polushkin
David Sellmyer Publications
The nanomagnetic behavior of Co–C nanodot arrays was investigated by magnetic force microscopy (MFM) and an alternative gradient force magnetometer. The direction of the easy axis can be observed directly with MFM by comparing the saturated magnetization state and the remanent magnetization state. Interaction of the domain wall with local defects was observed by field dependent MFM measurements. Some types of defects that can pin domain wall movement were identified.
Orientation-Controlled Nonepitaxial L10 Copt And Fept Films, H. Zeng, M.L. Yan, Nathan D. Powers, David J. Sellmyer
Orientation-Controlled Nonepitaxial L10 Copt And Fept Films, H. Zeng, M.L. Yan, Nathan D. Powers, David J. Sellmyer
David Sellmyer Publications
We report results on highly oriented, face-centered tetragonal ordered CoPt and FePt thin films grown nonepitaxially by directly depositing films on thermally oxidized Si substrates and subsequent annealing. By controlling the thickness, composition, and annealing conditions, and/or depositing a proper underlayer, nearly perfect (001)-oriented CoPt and FePt films can be obtained. Magnetic measurements reveal large perpendicular anisotropy for such films.
Structure And Magnetic Properties Of Ferromagnetic Nanowires In Self-Assembled Arrays, H. Zeng, Ralph Skomski, L. Menon, Yi Liu, Supriyo Bandyopadhyay, David J. Sellmyer
Structure And Magnetic Properties Of Ferromagnetic Nanowires In Self-Assembled Arrays, H. Zeng, Ralph Skomski, L. Menon, Yi Liu, Supriyo Bandyopadhyay, David J. Sellmyer
David Sellmyer Publications
Static and dynamic aspects of the magnetization reversal in nanowire arrays are investigated. The arrays have been produced by electrodeposition of ferromagnetic metals (Fe, Co, and Ni) into porous anodic alumina templates, with diameters as small as 5 nm. The crystal structures of the nanowires are bcc (Fe) and fcc (Ni) and a mixture of fcc and hcp (Co), with grain sizes of a few nanometers. Magnetic properties as a function of temperature are investigated. The temperature dependence of coercivity can be understood in terms of thermal activation over an energy barrier with a 3/2-power dependence on the field. Coercivity …
Pore Structure, Barrier Layer Topography And Matrix Alumina Structure Of Porous Anodic Alumina Film, Yucheng Sui, B.Z. Cui, L. Martinez, R. Perez, David J. Sellmyer
Pore Structure, Barrier Layer Topography And Matrix Alumina Structure Of Porous Anodic Alumina Film, Yucheng Sui, B.Z. Cui, L. Martinez, R. Perez, David J. Sellmyer
David Sellmyer Publications
Different anodic voltages and methods were adopted to produce porous anodic alumina films (PAAF) in an aqueous solution of oxalic acid. Carbon tube growth by chemical vapor deposition (CVD) in the films was used to copy the internal pore structure and was recorded by transmission electron microscopy (TEM) photos. Atomic force microscope (AFM) was employed to obtain the topography of the barrier layer of the corresponding films. When the anodic voltage was 40 V and the two-step method adopted, the barrier layer of the film had domains with highly ordered hexagonal cell distribution, and the corresponding pores were straight. When …
Transition From Negative Magnetoresistance Behavior To Positive Behavior In Co20 (Cu1-XGeX)80 Ribbons, J. He, Z.D. Zhang, J. Ping Liu, David J. Sellmyer
Transition From Negative Magnetoresistance Behavior To Positive Behavior In Co20 (Cu1-XGeX)80 Ribbons, J. He, Z.D. Zhang, J. Ping Liu, David J. Sellmyer
David Sellmyer Publications
We report a transition of the giant magnetoresistance (GMR) behavior in nanocrystalline Co20 (Cu1-xGex)80 ribbons from negative to positive, as the semiconductor Ge substitutes for the Cu matrix. The growth of the hexagonal Co3Ge2 compound leads to a change of the physical origin of the GMR. The normal spin-dependent transport behavior in the CoCu granular system evolves into Coulomb blockade behavior of electronic tunneling in ribbons with a Co/Co3Ge2/Co junctionlike configuration.
Effects Of Surface Morphology On Magnetic Properties Of Ni Nanowire Arrays In Self-Ordered Porous Alumina, H. Zeng, Stevem A. Michalski, Roger D. Kirby, David J. Sellmyer, L. Menon, Supriyo Bandyopadhyay
Effects Of Surface Morphology On Magnetic Properties Of Ni Nanowire Arrays In Self-Ordered Porous Alumina, H. Zeng, Stevem A. Michalski, Roger D. Kirby, David J. Sellmyer, L. Menon, Supriyo Bandyopadhyay
David Sellmyer Publications
Ni nanowire arrays were produced by electrodeposition of Ni into self-assembled porous anodic alumina templates. With different anodization voltages, the wires show different surface morphologies. The temperature dependence of the coercivity and activation volume of wires with regular shape can be explained by thermal activation over an energy barrier with a 3/2 power dependence on the field. The wires with irregular surface morphologies show abnormal temperature dependences of the coercivity and activation volume. Possible mechanisms for these behaviors are discussed.
Selected Reflection Imaging: A Useful Tool For Imaging Nanocomposite Magnetic Materials, Yi Liu, Y. Qiang, M. Yu, J. Ping Liu, David J. Sellmyer
Selected Reflection Imaging: A Useful Tool For Imaging Nanocomposite Magnetic Materials, Yi Liu, Y. Qiang, M. Yu, J. Ping Liu, David J. Sellmyer
David Sellmyer Publications
The great strength of transmission electron microscope (TEM) is its capability to access to both real space (imaging) and reciprocal space (diffraction). Selected reflection imaging (SRI) can relate the diffraction of nanostructured materials with the image, providing information otherwise not possible. The experimental set up of SRI is given by Liu and Sellmyer [I]. In this paper we present some new measurements on nanocomposite magnetic materials.
The Magnetism-Nanostructure Interface In Advanced Magnetic Materials, David J. Sellmyer
The Magnetism-Nanostructure Interface In Advanced Magnetic Materials, David J. Sellmyer
David Sellmyer Publications
The critical relationship between microstructure and nanostructure of materials and their magnetic properties has been appreciated for decades. Electromagnetic machinery, permanent magnets, and data recording and electronic devices all have seen steady and sometimes spectacular advances over this period. At the present time the most interesting research in magnetism and magnetic materials arises from new developments in structuring materials on the nanometer length scale. This talk will present recent advances and challenges in furthering this work, with particular attention paid to extremely high density magnetic recording films, exchange-coupled high-energy-product permanent-magnet materials, high-temperature permanent-magnet materials, and self-organized and patterned magnetic nanoarrays.
Elemental Mapping Of Co-Pr Nanostructured Powders By Eels Image Filtering, Yi Liu, C. Nelson, H. Tang, David J. Sellmyer
Elemental Mapping Of Co-Pr Nanostructured Powders By Eels Image Filtering, Yi Liu, C. Nelson, H. Tang, David J. Sellmyer
David Sellmyer Publications
In current extremely high density recording media design, the signal to noise ratio SNR is related to the number of magnetic grains N in a recording bit by
SNR = 10 logl0 N .................................... (1)
In earlier studies we have found that a metallurgical grain can act as a magnetic grain when grains are magnetically decoupled by a non-magnetic phase [1,2]. Alternatively, several metallurgical grains can be exchange-coupled together when they are small [3]. An ideal morphology is one in which the non-magnetic atoms are segregated at the grain boundaries forming the non-magnetic phase while keeping the grains closely …