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Full-Text Articles in Physics
Phase Composition And Nanostructure Of Zr2Co11-Based Alloys, Y.L. Jin, Wenyong Zhang, Ralph A. Skomski, Shah R. Valloppilly, Jeffrey E. Shield, David J. Sellmyer
Phase Composition And Nanostructure Of Zr2Co11-Based Alloys, Y.L. Jin, Wenyong Zhang, Ralph A. Skomski, Shah R. Valloppilly, Jeffrey E. Shield, David J. Sellmyer
David Sellmyer Publications
The effect of Mo addition on phase composition and nanostructure of nanocrystalline Zr16Co84-xMox (x=0–2.0) melt spun at 55 m/s has been investigated. All the ribbons consist mainly of a hard magnetic Zr2Co11 phase with rhombohedral crystal structure but also contain minor amounts of soft-magnetic phases. The increase in cell volume on alloying suggests that Mo mainly enters the rhombohedral Zr2Co11 structure and occupies the Co site. Mo addition promotes the formation of the hard magnetic phase and increases its volume fraction. The mean grain size of the hard magnetic …
Structural, Magnetic, And Electron Transport Properties Of Mn3-XPtXSn (X = 0, 0.5, 1) Nanomaterials, A Nelson, Yung Huh, Parashu Kharel, Shah R. Valloppilly, Ralph A. Skomski, David J. Sellmyer
Structural, Magnetic, And Electron Transport Properties Of Mn3-XPtXSn (X = 0, 0.5, 1) Nanomaterials, A Nelson, Yung Huh, Parashu Kharel, Shah R. Valloppilly, Ralph A. Skomski, David J. Sellmyer
David Sellmyer Publications
The structural, magnetic, and electron-transport properties of Mn3-xPtxSn (x=0, 0.5, 1) nanomaterials prepared by arc-melting, melt-spinning, and annealing were investigated. It was found that the hexagonal structure is the most stable structure for Mn3Sn and the samples show an antiferromagnetic spin order at room temperature. The Pt-containing samples are mainly tetragonal but contain a small amount of other impurity phases, including hexagonal Mn3Sn and Mn2Sn. At room temperature, the Pt-containing samples show ferri- or ferromagnetic spin order with a Curie temperature of about 370 K. The measured high-field magnetization and …
Magnetic Nanostructuring And Overcoming Brown’S Paradox To Realize Extraordinary High-Temperature Energy Products, Balamurugan Balasubramanian, Pinaki Mukherjee, Ralph A. Skomski, Priyanka Manchanda, Bhaskar Das, David J. Sellmyer
Magnetic Nanostructuring And Overcoming Brown’S Paradox To Realize Extraordinary High-Temperature Energy Products, Balamurugan Balasubramanian, Pinaki Mukherjee, Ralph A. Skomski, Priyanka Manchanda, Bhaskar Das, David J. Sellmyer
David Sellmyer Publications
Nanoscience has been one of the outstanding driving forces in technology recently, arguably more so in magnetism than in any other branch of science and technology. Due to nanoscale bit size, a single computer hard disk is now able to store the text of 3,000,000 average-size books, and today’s high-performance permanent magnets—found in hybrid cars, wind turbines, and disk drives—are nanostructured to a large degree. The nanostructures ideally are designed from Co- and Fe-rich building blocks without critical rare-earth elements, and often are required to exhibit high coercivity and magnetization at elevated temperatures of typically up to 180 °C for …
Size-Induced Chemical And Magnetic Ordering In Individual Fe–Au Nanoparticles, Pinaki Mukherjee, Priyanka Manchanda, Pankaj Kumar, Lin Zhou, Matthew J. Kramer, Arti Kashyap, Ralph Skomski, David J. Sellmyer, Jeffrey E. Shield
Size-Induced Chemical And Magnetic Ordering In Individual Fe–Au Nanoparticles, Pinaki Mukherjee, Priyanka Manchanda, Pankaj Kumar, Lin Zhou, Matthew J. Kramer, Arti Kashyap, Ralph Skomski, David J. Sellmyer, Jeffrey E. Shield
David Sellmyer Publications
Formation of chemically ordered compounds of Fe and Au is inhibited in bulk materials due to their limited mutual solubility. However, here we report the formation of chemically ordered L12-type Fe3Au and FeAu3 compounds in Fe–Au sub-10 nm nanoparticles, suggesting that they are equilib-rium structures in size-constrained systems. The stability of these L12-ordered Fe3Au and FeAu3 com-pounds along with a previously discovered L10-ordered FeAu has been explained by a size-dependent equilibrium thermodynamic model. Furthermore, the spin ordering of these three com-pounds has been computed using ab initio first-principle calculations. All ordered compounds exhibit a …
Magneto-Electric Control Of Surface Anisotropy And Nucleation Modes In L10-Copt Thin Films, Priyanka Manchanda, Pankaj Kumar, Hans Fangohr, David J. Sellmyer, Arti Kashyap, Ralph Skomski
Magneto-Electric Control Of Surface Anisotropy And Nucleation Modes In L10-Copt Thin Films, Priyanka Manchanda, Pankaj Kumar, Hans Fangohr, David J. Sellmyer, Arti Kashyap, Ralph Skomski
David Sellmyer Publications
The interplay between electric field-controlled surface magnetic anisotropy and micromagnetic nu-cleation modes for L10-CoPt thin films is investigated with density-functional and micromagnetic model calculations. The electric field redistributes electron states near the Fermi level, which has a fairly strong effect on the surface anisotropy, but due to inversion symmetry, the net anisotropy of the films with odd numbers of layers remains unchanged. By contrast, the micromagnetic nucleation mode is spatially asymmetric even for symmetric thin films with odd numbers of layers. This leads to a reduction of the nucleation field (coercivity) and—for suitably chosen nanostructures—to sub-stantial changes in …
Kondorski Reversal In Magnetic Nanowires, Ralph A. Skomski, Eva Schubert, Axel Enders, David J. Sellmyer
Kondorski Reversal In Magnetic Nanowires, Ralph A. Skomski, Eva Schubert, Axel Enders, David J. Sellmyer
David Sellmyer Publications
Magnetization reversal in nanowire systems, such as alnico-type permanent magnets, slanted columns produced by glancing-angle deposition, and nanowires embedded in alumina templates, is investigated by model calculations. The angular dependence of the domain-wall propagation is Kondorski-like, reminiscent of Kondorski pinning in bulk materials but with a somewhat different physics and consistent with Kerr hysteresis-loop measurements. Criss-cross patterning of alnicos improves the coercivity but reduces the remanence, with virtually zero net effect on energy product. Finally, we briefly discuss the wire-radius dependence of the coercivity in the context of "shape anisotropy" and the occurrence of interaction domains in alnico.
Magnetic Silicon Nanoparticles, Priyanka Manchanda, Pankaj Kumar, Balamurugan Balasubramanian, Pinaki Mukherjee, Arti Kashyap, David J. Sellmyer, Ralph Skomski
Magnetic Silicon Nanoparticles, Priyanka Manchanda, Pankaj Kumar, Balamurugan Balasubramanian, Pinaki Mukherjee, Arti Kashyap, David J. Sellmyer, Ralph Skomski
David Sellmyer Publications
Prospects for diamond-structured magnetic Si are investigated experimentally, by model calcula-tions, and numerically. Our theoretical analysis, using bond-orbital, Vienna ab-initio simulation pack-age, and SIESTA calculations, suggest that some diamond-Si imperfection may carry a magnetic moment. In particular, for tetrahedral Si5 clusters, we calculate a magnetic moment of 4 μB per cluster. These moments are more likely to be observed in nanoparticles, as compared with thin films, due to the larger surface-to-volume ratios of the former and to their more versatile atomic surface structure. Experimentally, we have prepared Si nanoparticles by cluster deposition and found a small magnet-ization of 2.9 …
Effect Of Annealing On Nanostructure And Magnetic Properties Of Zr2Co11 Material, Wenyong Zhang, Xingzhong Li, Shah R. Valloppilly, Ralph A. Skomski, David J. Sellmyer
Effect Of Annealing On Nanostructure And Magnetic Properties Of Zr2Co11 Material, Wenyong Zhang, Xingzhong Li, Shah R. Valloppilly, Ralph A. Skomski, David J. Sellmyer
David Sellmyer Publications
Single-phaseZr2Co11 nanomagnetic materials with high coercivity have been fabricated by melt spin-ning with subsequent annealing under Ar, N2, and vacuum. Annealing coarsens the grains and de-creases the density of defects, leading to intergrain decoupling action and the enhancement of the magnetocrystalline anisotropy field of the hard magnetic phase. Therefore, coercivity increases 44.7% from 6.7 kOe for the as-spun to 9.7 kOe for the annealed, which is the highest among Zr–Co alloys so far. The results show that the magnetic-hardening mechanism is primarily dominated by domain-wall pinning. In addition, annealing clearly increases the saturation magnetization. The …
Hf–Co And Zr–Co Alloys For Rare-Earth-Free Permanent Magnets, Balamurugan Balasubramanian, Bhaskar Das, Wenyong Zhang, Ralph Skomski, David J. Sellmyer
Hf–Co And Zr–Co Alloys For Rare-Earth-Free Permanent Magnets, Balamurugan Balasubramanian, Bhaskar Das, Wenyong Zhang, Ralph Skomski, David J. Sellmyer
David Sellmyer Publications
The structural and magnetic properties of nanostructured Co-rich transition-metal alloys, Co100-xTMx (TM = Hf, Zr and 10 ≤ x ≤ 18), were investigated. The alloys were prepared under nonequilibrium conditions using cluster-deposition and/or melt-spinning methods. The high-anisotropy HfCo7 and Zr2Co11 structures were formed for a rather broad composition region as compared to the equilibrium bulk phase diagrams, and exhibit high Curie temperatures of above 750 K. The composition, crystal structure, particle size, and easy-axis distribution were precisely controlled to achieve a substantial coercivity and magnetization in the nanostructured alloys. This translates into high …
Orthorhombic Zr2Co11 Phase Revisited, Xingzhong Li, Wenyong Zhang, David J. Sellmyer, X Zhao, M C. Nguyen, C Z. Wang, K M. Ho
Orthorhombic Zr2Co11 Phase Revisited, Xingzhong Li, Wenyong Zhang, David J. Sellmyer, X Zhao, M C. Nguyen, C Z. Wang, K M. Ho
David Sellmyer Publications
The structure of the orthorhombic Zr2Co11 phase was revisited in the present work. Selected-area electron diffraction (SAED) and high-resolution electron microscopy (HREM) techniques were used to investigate the structure. They show the orthorhombic Zr2Co11 phase has a 1-D incommensurate modulated structure. The structure can be approximately described as a B-centered orthorhombic lattice. The lattice parameters of the orthorhombic Zr2Co11 phase have been determined by a tilt series of SAED patterns. A hexagonal network with a modulation wave has been observed in the HREM image and the hexagonal motif is considered as …
Adjusting Magnetic Nanostructures For High-Performance Magnetic Sensors, Xiaolu Yin, Ralph A. Skomski, David J. Sellmyer, Sy-Hwang Liou, Stephen E. Russek, Eric R. Evarts, John Moreland, A S. Edelstein, L Yuan, M L. Yan, J Shen
Adjusting Magnetic Nanostructures For High-Performance Magnetic Sensors, Xiaolu Yin, Ralph A. Skomski, David J. Sellmyer, Sy-Hwang Liou, Stephen E. Russek, Eric R. Evarts, John Moreland, A S. Edelstein, L Yuan, M L. Yan, J Shen
David Sellmyer Publications
The magnetic properties of the soft ferromagnetic layer in magnetic tunnel junctions are one of key factors to determine the performance of magnetoresistance sensors. We use a three-step orthogonal annealing procedure to modify the nanostructures of the free layer in the magnetic tunnel junction to control features such as magnetization reversal, coercivity, exchange field, and tunnel magnetoresistance ratio. We present a sensor with an improved sensitivity as high as 3944%/mT. This magnetic sensor only dissipates 200 lW of power while operating under an applied voltage of 1V.
Development And Intrinsic Properties Of Hexagonal Ferromagnetic (Zr,Ti)Fe2, Wenyong Zhang, Xingzhong Li, Shah R. Valloppilly, Ralph A. Skomski, Jeffrey E. Shield, David J. Sellmyer
Development And Intrinsic Properties Of Hexagonal Ferromagnetic (Zr,Ti)Fe2, Wenyong Zhang, Xingzhong Li, Shah R. Valloppilly, Ralph A. Skomski, Jeffrey E. Shield, David J. Sellmyer
David Sellmyer Publications
Nanocrystalline Ti0.75Zr0.25Fe2+x (x=0-0.4) and Ti0.75-yByZr0.25Fe2.4 (y=0-0.35) with high saturation magnetization have been fabricated by the melt-spinning technique. Nanocrystalline Ti0.75Zr0.25Fe2+x consists of the hexagonal C14 Laves phase (Ti,Zr)Fe2. Fe addition decreases the lattice parameter a and shrinks the cell volume. The antiferromagnetic Fe-Fe interactions may decrease with the increase of x, leading to a significant enhancement of saturation polarization (Js) and Curie temperature (Tc). The magnetocrystalline anisotropy constant K also increases with increasing x. Excessive Fe addition (x>0.25) may induce structural …
Effect Of Quench Rate On Nanostructure And Magnetic Properties Of Prco5, Wenyong Zhang, Ralph Skomski, Xingzhong Li, Shah R. Valloppilly, Jeffrey E. Shield, David J. Sellmyer
Effect Of Quench Rate On Nanostructure And Magnetic Properties Of Prco5, Wenyong Zhang, Ralph Skomski, Xingzhong Li, Shah R. Valloppilly, Jeffrey E. Shield, David J. Sellmyer
David Sellmyer Publications
The effect of quench rate on nanostructure and magnetic properties of PrCo5 alloy has been investigated. The increase of quench rate through wheel speed in melt spinning suppresses the formation of the secondary Pr2Co17 and Pr5Co19 phases with low magnetocrystalline anisotropy field and refines the nanostructure. This significantly improves the coercivity, remanence, and energy product. For example, increasing the wheel speed from 30 m/s to 70 m/s increases the coercivity and energy product from 3.2 kOe and 4.0 MGOe to 10.3 kOe and 13.7 MGOe, respectively. The magnetic hardening mechanism appears to be …
Exploring The Structural Complexity Of Intermetallic Compounds By An Adaptive Genetic Algorithm, X Zhao, M C. Nguyen, Wenyong Zhang, C Z. Wang, Matthew J. Kramer, David J. Sellmyer, Xingzhong Li, F Zhang, Liqin Ke, Vladimir P. Antropov, K M. Ho
Exploring The Structural Complexity Of Intermetallic Compounds By An Adaptive Genetic Algorithm, X Zhao, M C. Nguyen, Wenyong Zhang, C Z. Wang, Matthew J. Kramer, David J. Sellmyer, Xingzhong Li, F Zhang, Liqin Ke, Vladimir P. Antropov, K M. Ho
David Sellmyer Publications
Solving the crystal structures of novel phases with nanoscale dimensions resulting from rapid quenching is difficult due to disorder and competing polymorphic phases. Advances in computer speed and algorithm sophistication have now made it feasible to predict the crystal structure of an unknown phase without any assumptions on the Bravais lattice type, atom basis, or unit cell dimensions, providing a novel approach to aid experiments in exploring complex materials with nanoscale grains. This approach is demonstrated by solving a long-standing puzzle in the complex crystal structures of the orthorhombic, rhombohedral, and hexagonal polymorphs close to the Zr2Co11 …
Magnetic Hardening Of Zr2Co11:(Ti, Si) Nanomaterials, Wenyong Zhang, Shah R. Valloppilly, Xingzhong Li, Yi Liu, Steven A. Michalski, T A. George, Ralph A. Skomski, David J. Sellmyer
Magnetic Hardening Of Zr2Co11:(Ti, Si) Nanomaterials, Wenyong Zhang, Shah R. Valloppilly, Xingzhong Li, Yi Liu, Steven A. Michalski, T A. George, Ralph A. Skomski, David J. Sellmyer
David Sellmyer Publications
The role of Ti and Si additions in the magnetic hardening of rapidly quenched Zr2Co11-based nano-materials has been investigated. Nanocrystalline Zr17–xTixCo83 and Zr18Co82–ySiy are mainly composed of rhombohedral Zr2Co11 and a small amount of orthorhombic Zr2Co11, hcp Co, and cubic Zr6Co23. Ti addition decreases the mean grain size of the magnetic phases, and thus increases coercivity and energy product from 1.6 kOe and 1.9 MGOe for x = 0 to 2.6 kOe and 3.9 MGOe …
Permanent Magnetism Of Intermetallic Compounds Between Light And Heavy Transition-Metal Elements, P Kumar, Arti Kashyap, Balamurugan Balamurugan, Jeffrey E. Shield, David J. Sellmyer, Ralph Skomski
Permanent Magnetism Of Intermetallic Compounds Between Light And Heavy Transition-Metal Elements, P Kumar, Arti Kashyap, Balamurugan Balamurugan, Jeffrey E. Shield, David J. Sellmyer, Ralph Skomski
David Sellmyer Publications
First principle calculations are used to investigate the intrinsic magnetic properties of intermetallic alloys of the type XMn, where X is a 4d or 5d element and M is Fe or Co. Emphasis is on the hexagonal C14 Laves-phase 1:2 and 1:5 alloys, the latter crystallizing in the CaCu5 structure. These series are of interest in permanent magnetism from fundamental and practical viewpoints, respectively. In the former, the unit cells form a prototypical motif where a heavy atom with high spin-orbit coupling and magnetocrystalline anisotropy is surrounded by many somewhat smaller M atoms with high magnetization, …
Direct Chemical Synthesis Of L10-Feptau Nanoparticles With High Coercivity, Yongsheng Yu, Pinaki Mukherjee, Yuan Tian, Xingzhong Li, David J. Sellmyer
Direct Chemical Synthesis Of L10-Feptau Nanoparticles With High Coercivity, Yongsheng Yu, Pinaki Mukherjee, Yuan Tian, Xingzhong Li, David J. Sellmyer
David Sellmyer Publications
We report a facile synthesis of hard magnetic L10-FePtAu nanoparticles by coreduction of Fe(acac)3, Pt(acac)2 (acac = acetylacetonate), and gold acetate in oleylamine. In the current reaction condition, NP sizes are controlled to be 5.5 to 11.0 nm by changing the amount of Au doping. When the Au composition in the NPs is higher than 14%, the hard magnetic NPs are directly obtained without any annealing. The highest coercivity of 12.15 kOe at room temperature could be achieved for the NPs with 32% Au doping, which is much higher than the coercivities reported by the …
Monodisperse Mpt (M = Fe, Co, Ni, Cu, Zn) Nanoparticles Prepared From A Facile Oleylamine Reduction Of Metal Salts, Yongsheng Yu, Weiwei Yang, Xiaolian Sun, Wenlei Zhu, Xingzhong Li, David J. Sellmyer, Shouheng Sun
Monodisperse Mpt (M = Fe, Co, Ni, Cu, Zn) Nanoparticles Prepared From A Facile Oleylamine Reduction Of Metal Salts, Yongsheng Yu, Weiwei Yang, Xiaolian Sun, Wenlei Zhu, Xingzhong Li, David J. Sellmyer, Shouheng Sun
David Sellmyer Publications
We report a simple yet general approach to monodisperse MPt (M = Fe, Co, Ni, Cu, Zn) nanoparticles (NPs) by coreduction of M(acac)2 and Pt(acac)2 (acac = acetylacetonate) with oleylamine at 300°C. In the current reaction condition, oleylamine serves as the reducing agent, surfactant, and solvent. As an example, we describe in details the synthesis of 9.5 nm CoPt NPs with their compositions con-trolled from Co37Pt63 to Co69Pt31. These NPs show composition-dependent structural and magnetic properties. The unique oleylamine reduction process makes it possible to prepare MPt NPs with their physical …