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Full-Text Articles in Physics
Magnetic And Spectroscopic Characteristics Of Znmno System, Aswini K. Pradhan, D. Hunter, Kai Zhang, J.B. Dadson, S. Mohanty, T.M. Williams, K. Lord, R.R. Rakimhov, U.N. Roy, Y. Cui, A. Burger, Jun Zhang, David J. Sellmyer
Magnetic And Spectroscopic Characteristics Of Znmno System, Aswini K. Pradhan, D. Hunter, Kai Zhang, J.B. Dadson, S. Mohanty, T.M. Williams, K. Lord, R.R. Rakimhov, U.N. Roy, Y. Cui, A. Burger, Jun Zhang, David J. Sellmyer
David Sellmyer Publications
We report on the observation of room-temperature ferromagnetism in epitaxial (Zn,Mn)O films grown by a pulsed-laser deposition technique using high-density targets. The X-ray, microscopic, spectroscopic and magnetic properties of target material containing 6 at.% of Mn and films were compared. The target shows the presence of large clusters exhibiting paramagnetic behavior. However, ferromagnetic properties were observed in (Zn,Mn)O films grown at a substrate temperature of 500 °C and with an oxygen partial pressure of 1 mTorr. Although, crystalline quality of the film improves with increasing substrate temperature, the ferromagnetism becomes weaker.
Ferromagnetism In Nanocrystalline Epitaxial Co:Tio2 Thin Films, Aswini K. Pradhan, D. Hunter, J.B. Dadson, T.M. Williams, Kai Zhang, K. Lord, B. Lasley, Rakhim R. Rakhimov, Jun Zhang, David J. Sellmyer, U.N. Roy, Y. Cui, A. Burger, C. Hopkins, N. Pearson, A.L. Wilkerson
Ferromagnetism In Nanocrystalline Epitaxial Co:Tio2 Thin Films, Aswini K. Pradhan, D. Hunter, J.B. Dadson, T.M. Williams, Kai Zhang, K. Lord, B. Lasley, Rakhim R. Rakhimov, Jun Zhang, David J. Sellmyer, U.N. Roy, Y. Cui, A. Burger, C. Hopkins, N. Pearson, A.L. Wilkerson
David Sellmyer Publications
We report on the observation of remarkable room-temperature ferromagnetism in nanocrystalline epitaxial Co:TiO2 films grown on sapphire (0001) substrates by a pulsed-laser deposition technique using high-density targets. The films were characterized by x-ray measurements, atomic force microscopy, micro-Raman, electron-paramagnetic resonance, and magnetization studies. The films exhibit three-dimensional islandlike growth that contains nanocrystalline particles. Our experimental results suggest that the remarkable ferromagnetism in Co:TiO2 films is controlled either by the interstitial Co2+ ions or small clusters, which are mainly present at the interface and on the surface of the films. Our work clearly indicates that Co interstitials and …
Magnetic Properties Of Dilute Fept:C Nanocluster Films, Yinfan Xu, M.L. Yan, J. Zhou, David J. Sellmyer
Magnetic Properties Of Dilute Fept:C Nanocluster Films, Yinfan Xu, M.L. Yan, J. Zhou, David J. Sellmyer
David Sellmyer Publications
Nanocluster-assembled dilute (FePt) xC100-x films with 30≥x≥5 (x denotes volume fraction) were produced using a gas-aggregation technique. FePt clusters with an average size of about 4.0 nm (with standard deviation σ /d=0.09) were embedded in high volume fraction of carbon matrix, which is used to isolate the FePt clusters. Postdeposition annealing was used to realize the high-anisotropy L10 phase. Single-crystal features of well-isolated clusters were observed by transmission electron microscope (TEM) in annealed dilute films. The coercivity of the films annealed at 700 °C for 5 min was a few hundred Oersteds at room temperature, while …
Relaxation In Magnetic Nanostructures, Ralph Skomski, J. Zhou, David J. Sellmyer
Relaxation In Magnetic Nanostructures, Ralph Skomski, J. Zhou, David J. Sellmyer
David Sellmyer Publications
The damping of magnetization processes in nanostructures is investigated by Fokker–Planck-type model calculations and quantum-mechanical considerations based on Fermi's golden rule. In the absence of energy barriers, the problem reduces to a magnetic diffusion equation with a particle-size-dependent diffusivity which is indirectly proportional to the relaxation-time parameter τo. For small particles, the relaxation time is proportional to the particle volume, but when the particle size reaches a few nanometers, it approaches a constant bulk value.
Rapidly Annealed Exchange-Coupled Sm-Co/Co Multilayers, J. Zhou, Ralph Skomski, Yi Liu, Yucheng Sui, W. Liu, David J. Sellmyer
Rapidly Annealed Exchange-Coupled Sm-Co/Co Multilayers, J. Zhou, Ralph Skomski, Yi Liu, Yucheng Sui, W. Liu, David J. Sellmyer
David Sellmyer Publications
In exchange-coupled two-phase permanent magnets, the length scale of soft phase is limited to about twice of the domain-wall width of the hard phase. To optimize the energy product, it is important to realize this length experimentally. In this work, we investigate the Sm–Co/Co hard/soft multilayers with varying thickness of soft phase layers. On rapidly annealing, the multilayered hard-soft structure forms. Transmission electron microscopy micrography confirms that the multilayer structure is retained after the annealing. Single-phase-like hysteresis loops are obtained for samples with Co layers up to 13 nm thick. This behavior indicates that the soft phase is well exchange …
Template-Mediated Assembly Of Fept L10 Clusters Under External Magnetic Field, Yucheng Sui, W. Liu, Lanping Yue, Xingzhong Li, J. Zhou, Ralph Skomski, David J. Sellmyer
Template-Mediated Assembly Of Fept L10 Clusters Under External Magnetic Field, Yucheng Sui, W. Liu, Lanping Yue, Xingzhong Li, J. Zhou, Ralph Skomski, David J. Sellmyer
David Sellmyer Publications
FePt L10-structured clusters were synthesized by hydrogen reduction of Fe(NO3)3•9H2O and H2PtCl6•6H2O mixtures within the pores of alumina. They were released by dissolving the alumina matrix and capped with organic surfactants. After a series of chemical treatments, clusters with an average diameter of about 11 nm were precipitated. The clusters were drop casted onto ordered nanoporous arrays. Clusters reaching the bottom of the pores formed an ordered magnetic array. The corresponding magnetic film exhibits distinct anisotropic behavior caused by the external magnetic field.
Cluster-Assembled Exchange-Spring Nanocomposite Permanent Magnets, X. Rui, Zhiguang Sun, Yinfan Xu, David J. Sellmyer, Jeffrey E. Shield
Cluster-Assembled Exchange-Spring Nanocomposite Permanent Magnets, X. Rui, Zhiguang Sun, Yinfan Xu, David J. Sellmyer, Jeffrey E. Shield
David Sellmyer Publications
Isotropic nanocomposite magnetic structures were produced via cluster assembly routes with energy products reaching 18 MG Oe. Gas aggregation produces Fe clusters with an average size less than 10 nm with a very narrow size distribution, and these were embedded in a hard magnetic matrix by cosputtering of FePt. Structures produced were crystallographically isotropic with Fe cluster phase content ranging from 0 to 30 vol %. The coercivity decreased from 13 kOe as Fe cluster content increased. Single-phase-type hysteresis loops indicating excellent exchange coupling at low Fe cluster content give way to a stepped demagnetization loop at an Fe cluster …
Anisotropic Exchange, Ralph Skomski, Arti Kashyap, Jian Zhou, David J. Sellmyer
Anisotropic Exchange, Ralph Skomski, Arti Kashyap, Jian Zhou, David J. Sellmyer
David Sellmyer Publications
The origin and physical nature anisotropic exchange interactions is investigated. Emphasis is on nonrelativistic exchange anisotropies, as encountered, for example, in intermetallics with layered crystal structures. The summation of site-resolved exchange interactions is analyzed, and it is shown that Ruderman–Kittel-type long-range exchange yield converging exchange-stiffness expressions down to atomic length scales. In general, the resulting exchange stiffness is anisotropic, even if the interaction is mediated by an isotropic free electron gas. The determination of the mean-field Curie temperature from pair-exchange interactions requires the diagonalization of an interaction matrix, as opposed to simple site averaging.
The Effects Of The Thickness Of Magnetically Hard- And Soft-Phase Layers On Magnetic Properties And Exchange Coupling In Multilayer Magnets, W. Liu, Yucheng Sui, J. Zhou, X.K. Sun, C.L. Chen, Z.D. Zhang, David J. Sellmyer
The Effects Of The Thickness Of Magnetically Hard- And Soft-Phase Layers On Magnetic Properties And Exchange Coupling In Multilayer Magnets, W. Liu, Yucheng Sui, J. Zhou, X.K. Sun, C.L. Chen, Z.D. Zhang, David J. Sellmyer
David Sellmyer Publications
The structure and magnetic properties of multilayer magnets containing a hard phase [HP≡ (Nd0.95Dy0.05)(Fe,Co,Nb,B) 5.5] and a soft phase (SP≡Fe and Fe65Co35) have been investigated. For the nanocomposite multilayer of Si(substrate)/Ti(30 nm)/[HP(x nm)/SP(y nm)] n/Ti(30 nm), the remanence enhancement has been observed at different thickness and volume fractions of hard- and soft-phase layers. The remanence increases and the coercivity decreases with the addition of soft phase, in comparison with the results of the single-layer film. For the multilayer of Si(substrate)/Ti(30 nm)/[HP(15 nm)/Fe(5 nm)] n/Ti(30 nm) annealed at …
Enhanced Coercivity In Thermally Processed (Nd,Dy)(Fe,Co,Nb,B) 5.5/ Α-Fe Nanoscale Multilayer Magnets, W. Liu, Xingzhong Li, J Ping Liu, X.K. Sun, C.L. Chen, Ralph Skomski, Z.D. Zhang, David J. Sellmyer
Enhanced Coercivity In Thermally Processed (Nd,Dy)(Fe,Co,Nb,B) 5.5/ Α-Fe Nanoscale Multilayer Magnets, W. Liu, Xingzhong Li, J Ping Liu, X.K. Sun, C.L. Chen, Ralph Skomski, Z.D. Zhang, David J. Sellmyer
David Sellmyer Publications
Structural and magnetic properties of laminated (Nd,Dy)(Fe,Co,Nb,B)5.5/Fe nanocomposites are investigated. Normally, the addition of the soft phase to the hard phase enhances the remanence but deteriorates the permanent-magnet performance of the material by reducing the coercivity. In the present system, the coercivity increases to 1608 kA/m (20.2 kOe) in thermally processed Nd–Dy–Fe–Co–Nb–B(15 nm)/Fe(4 nm) multilayered nanocomposites, which is higher than that of the single-layer hard-magnetic film. The abnormally high coercivity is achieved by annealing at relatively high temperature, which breaks the laminated structure of the as-deposited multilayer. A likely physical explanation of the enhanced coercivity is the introduction …
Sample Preparation And Annealing Effects On The Ferromagnetism In Mn-Doped Zno, Jun Zhang, Ralph Skomski, David J. Sellmyer
Sample Preparation And Annealing Effects On The Ferromagnetism In Mn-Doped Zno, Jun Zhang, Ralph Skomski, David J. Sellmyer
David Sellmyer Publications
Magnetic properties of Mn-doped ZnO strongly depend on sample preparation and annealing. While the samples sintered in air at 500 °C show ferromagnetism at room temperature, those sintered at 900 °C are paramagnetic. The samples sintered in vacuum show a ferromagnetic transition at 45 K, which is attributed to ferrimagnetic Mn3O4. With an increase of annealing temperature, the ferromagnetism observed at room temperature in the low-temperature-sintered samples is gradually suppressed and finally completely removed. These results can be understood by considering a metastable ferromagnetic phase and its stability under varying temperatures and atmospheres.
Highly (001)-Oriented Ni-Doped L10 Fept Films And Their Magnetic Properties, M.L. Yan, Yinfan Xu, Xingzhong Li, David J. Sellmyer
Highly (001)-Oriented Ni-Doped L10 Fept Films And Their Magnetic Properties, M.L. Yan, Yinfan Xu, Xingzhong Li, David J. Sellmyer
David Sellmyer Publications
We report on Ni-doped nonepitaxial L10 FePt thin films with strong (001) texture. The influences of Ni doping on L10 ordering, orientation, and the magnetic properties of the FePt films have been investigated. In-plane and out-of-plane x-ray diffractions (XRD) were used to analyze the texture of FeNiPt films. For [Fe(0.38 nm)/Ni(0.04 nm)/Pt(0.4)] 13 sample, the out-of-plane XRD data showed only (00l) peaks and in-plane data showed (hk0) peaks after annealing, indicating high (001) texture of the FeNiPt films. In comparison with FePt, the (00l) peak positions shifted to higher angle, …
Magnetic And Electrical Properties Of Single-Phase Multiferroic Bifeo3, Aswini K. Pradhan, Kai Zhang, D. Hunter, J.B. Dadson, G.B. Loiutts, P. Bhattacharya, R. Katiyar, Jun Zhang, David J. Sellmyer, U.N. Roy, Y. Cui, A. Burger
Magnetic And Electrical Properties Of Single-Phase Multiferroic Bifeo3, Aswini K. Pradhan, Kai Zhang, D. Hunter, J.B. Dadson, G.B. Loiutts, P. Bhattacharya, R. Katiyar, Jun Zhang, David J. Sellmyer, U.N. Roy, Y. Cui, A. Burger
David Sellmyer Publications
We have reported the structural, thermal, microscopic, magnetization, polarization, and dielectric properties of BiFeO3 ceramics synthesized by a rapid liquid-phase sintering technique. Optimum conditions for the synthesis of single-phase BiFeO3 ceramics were obtained. Temperature-dependent magnetization and hysteresis loops indicate antiferromagnetic behavior in BiFeO3 at room temperature. Although saturated ferroelectric hysteresis loops were observed in single-phase BiFeO3 ceramic synthesized at 880 °C, the reduced polarization is found to be due to the high loss and low dielectric permittivity of the ceramic, which is caused by higher leakage current.
High-Temperature Ferromagnetism In Pulsed-Laser Deposited Epitaxial (Zn,Mn)O Thin Films: Effects Of Substrate Temperature, Aswini K. Pradhan, Kai Zhang, S. Mohanty, J.B. Dadson, D. Hunter, Jun Zhang, David J. Sellmyer, U.N. Roy, Y. Cui, A. Burger, S. Mathews, B. Joseph, B.R. Sekhar, B.K. Roul
High-Temperature Ferromagnetism In Pulsed-Laser Deposited Epitaxial (Zn,Mn)O Thin Films: Effects Of Substrate Temperature, Aswini K. Pradhan, Kai Zhang, S. Mohanty, J.B. Dadson, D. Hunter, Jun Zhang, David J. Sellmyer, U.N. Roy, Y. Cui, A. Burger, S. Mathews, B. Joseph, B.R. Sekhar, B.K. Roul
David Sellmyer Publications
We report on the observation of remarkable room-temperature ferromagnetism in epitaxial (Zn,Mn)O films grown by a pulsed-laser deposition technique using high-density targets. The optimum growth conditions were demonstrated from x-ray measurements, microstructure, Rutherford backscattering, micro-Raman, and magnetic studies. Superior ferromagnetic properties were observed in (Zn,Mn)O films grown at a substrate temperature of 500 °C and with an oxygen partial pressure of 1 mTorr. Ferromagnetism becomes weaker with increasing substrate temperature due to the formation of isolated Mn clusters irrespective of higher crystalline quality of the film.
Integration Of Epitaxial Colossal Magnetoresistive Films Onto Si(100) Using Srtio3 As A Template Layer, Aswini K. Pradhan, S. Mohanty, Kai Zhang, J.B. Dadson, E.M. Jackson, D. Hunter, Rakhim R. Rakhimov, G.B. Loutts, Jun Zhang, David J. Sellmyer
Integration Of Epitaxial Colossal Magnetoresistive Films Onto Si(100) Using Srtio3 As A Template Layer, Aswini K. Pradhan, S. Mohanty, Kai Zhang, J.B. Dadson, E.M. Jackson, D. Hunter, Rakhim R. Rakhimov, G.B. Loutts, Jun Zhang, David J. Sellmyer
David Sellmyer Publications
We report on the integration of epitaxial colossal magnetoresistive La0.67Ba0.33MnO films on Si(100) semiconductor using SrTiO3 template layer by pulsed-laser deposition. X-ray diffraction reveals the superior quality of the manganite film that grows epitaxially on heteroepitaxially grown SrTiO3 template layer on Si substrate. The epitaxial films demonstrate remarkable surface morphology, magnetic transition and hysteresis, magnetoresistance, and ferromagnetic resonance, illustrating the ferromagnetic nature of the film and possible device applications at room temperature.