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Articles 1 - 30 of 278
Full-Text Articles in Physics
A Tem Study Of Fe3+X Co3-XTi2 (X = 0, 1, 2, 3) Intermetallic Alloys, Xingzhong Li, Anandakumar Sarella, B. Balasubramanian, Shah R. Valloppilly
A Tem Study Of Fe3+X Co3-XTi2 (X = 0, 1, 2, 3) Intermetallic Alloys, Xingzhong Li, Anandakumar Sarella, B. Balasubramanian, Shah R. Valloppilly
David Sellmyer Publications
A TEM study has been carried out on crystal structures in the rare-earth-free intermetallic alloys, Fe3+xCo3-xTi2 (x = 0, 1, 2, 3). These alloys have been demonstrated to have potentially high magnetic anisotropy. In these alloys, the main intermetallic compound was recently reported as a new hexagonal phase with a space group of P-6 m2. The present study reveals that the main compound belongs to Laves C14 variant surrounded by α-Fe type crystal as secondary phase in the Fe3+xCo3-xTi2 (x = 0, 1, 2, 3) alloys, in agreement with the …
Unusual Perpendicular Anisotropy In Co2Tisi Films, Yunlong Jin, Shah R. Valloppilly, Parashu R. Kharel, Rohit Pathak, Arti Kashyap, Ralph Skomski, David J. Sellmyer
Unusual Perpendicular Anisotropy In Co2Tisi Films, Yunlong Jin, Shah R. Valloppilly, Parashu R. Kharel, Rohit Pathak, Arti Kashyap, Ralph Skomski, David J. Sellmyer
David Sellmyer Publications
Thin films of Co2TiSi on MgO are investigated experimentally and theoretically. The films were produced by magnetron sputtering on MgO(001) and have a thickness of about 100 nm. As bulk Co2TiSi, they crystallize in the normal cubic Heusler (L21) structure, but the films are slightly distorted (c/a = 1.0014) and contain some antisite disorder. The films exhibit a robust perpendicular anisotropy of 0.5 MJ m−3. This result is surprising for several reasons. First, surface and interface anisotropies are too small to explain perpendicular anisotropy in such rather thick …
Magnetism Of Hexagonal Mn1.5X0.5Sn (X = Cr, Mn, Fe, Co) Nanomaterials, R Fuglsby, Parashu Kharel, Wenyong Zhang, Shah R. Valloppilly, Yung Huh, David J. Sellmyer
Magnetism Of Hexagonal Mn1.5X0.5Sn (X = Cr, Mn, Fe, Co) Nanomaterials, R Fuglsby, Parashu Kharel, Wenyong Zhang, Shah R. Valloppilly, Yung Huh, David J. Sellmyer
David Sellmyer Publications
Mn1.5X0.5Sn (X = Cr, Mn, Fe, Co) nanomaterials in the hexagonal Ni2In-type crystal structure have been prepared using arc-melting and melt spinning. All the rapidly quenched Mn1.5X0.5Sn alloys show moderate saturation magnetizations with the highest value of 458 emu/cm3 for Mn1.5Fe0.5Sn, but their Curie temperatures are less than 300K. All samples except the Cr containing one show spin-glass-like behavior at low temperature. The magnetic anisotropy constants calculated from the high-field magnetization curves at 100K are on the order of 1 Merg/cm3. The vacuum annealing of the ribbons at 550 C significantly improved their magnetic properties with the Curie temperature increasing …
Synthesis And Magnetism Of Single-Phase Mn-Ga Films, Wenyong Zhang, Parashu Kharel, Shah R. Valloppilly, Ralph A. Skomski, David J. Sellmyer
Synthesis And Magnetism Of Single-Phase Mn-Ga Films, Wenyong Zhang, Parashu Kharel, Shah R. Valloppilly, Ralph A. Skomski, David J. Sellmyer
David Sellmyer Publications
Single-phase noncubic Mn-Ga films with a thickness of about 200 nm were fabricated by an in situ annealing of [Mn(x)/Ga(y)/Mn(x)]5 multilayers deposited by e-beam evaporation. Mn-Ga alloys prepared in three different compositions Mn2Ga5 and Mn2Ga were found to crystallize in the tetragonal tP14 and tP2 structures, respectively. Mn3Ga crystallizes in the hexagonal hp8 or tetragonal tI8 structures. All three alloys show substantial magnetocrystalline anisotropy between 7 and 10 Mergs/cm3. The samples show hard magnetic properties including coercivities of Mn2Ga5 and Mn2Ga about 12.0 kOe and of Mn3Ga about 13.4 kOe. The saturation magnetization and Curie temperature of Mn2Ga5, Mn2Ga, and …
Enhancement Of Curie Temperature In Mn2rusn By Co Substitution, A Nelson, Parashu Kharel, Yung Huh, R Fuglsby, J Guenther, Wenyong Zhang, B Staten, Pavel V. Lukashev, David J. Sellmyer
Enhancement Of Curie Temperature In Mn2rusn By Co Substitution, A Nelson, Parashu Kharel, Yung Huh, R Fuglsby, J Guenther, Wenyong Zhang, B Staten, Pavel V. Lukashev, David J. Sellmyer
David Sellmyer Publications
The Co-substituted Mn2RuSn nanomaterials, namely, Mn2Ru0.5Co0.5Sn and Mn2Ru0.35Co0.65Sn have been synthesized and investigated. The presence of Co in the Mn2RuSn (a¼6.21A ° ) decreased the lattice parameter, where a¼6.14A ° and 6.12A ° for the as prepared Mn2Ru0.5Co0.5Sn and Mn2Ru0.35Co0.65Sn, respectively. The samples show a ferrimagnetic spin order with relatively small coercivities, similar to those of soft magnetic materials. There is a substantial increase in the Curie temperature (Tc¼448K for Mn2Ru0.5Co0.5Sn and 506K for Mn2Ru0.35Co0.65Sn) of Mn2RuSn (Tc¼272.1 K) due to Co substitution, which is a result of strengthening of the positive exchange interaction in this material. These materials are …
Novel Structures And Physics Of Nanomagnets (Invited), David J. Sellmyer, Balamurugan Balamurugan, Bhaskar Das, P Murherjee, Ralph A. Skomski, George C. Hadjipanayis
Novel Structures And Physics Of Nanomagnets (Invited), David J. Sellmyer, Balamurugan Balamurugan, Bhaskar Das, P Murherjee, Ralph A. Skomski, George C. Hadjipanayis
David Sellmyer Publications
Nanoscale magnets with characteristic dimensions in the range of 1–100 nm are important in several areas of nanoscience and technology. First, this length scale spans the typical important dimensions of exchange lengths and domain-wall widths, which means that significant control of magnetic properties can be obtained by varying grain or particle dimensions. Second, the nonequilibrium synthetic processes used for clusters, particles, and films, often lead to new real-space crystal structures with completely novel spin structures and magnetic properties. Third, a basic-science challenge in this class of matter involves the spin-polarized quantum mechanics of many-electron systems containing 10–10 000 atoms. Finally, …
Magnetism Of Ta Dichalcogenide Monolayers Tuned By Strain And Hydrogenation, Priyanka Manchanda, Vinit Sharma, Hongbin Yu, David J. Sellmyer, Ralph A. Skomski
Magnetism Of Ta Dichalcogenide Monolayers Tuned By Strain And Hydrogenation, Priyanka Manchanda, Vinit Sharma, Hongbin Yu, David J. Sellmyer, Ralph A. Skomski
David Sellmyer Publications
The effects of strain and hydrogenation on the electronic, magnetic, and optical properties of monolayers of Ta based dichalcogenides (TaX2; X=S, Se, and Te) are investigated using densityfunctional theory. We predict a complex scenario of strain-dependent magnetic phase transitions involving paramagnetic, ferromagnetic, and modulated antiferromagnetic states. Covering one of the two chalcogenide surfaces with hydrogen switches the antiferromagnetic/nonmagnetic TaX2 monolayers to a semiconductor, and the optical behavior strongly depends on strain and hydrogenation. Our research opens pathways towards the manipulation of magnetic as well as optical properties for future spintronics and optoelectronics applications
Magnetism Of Fept Nanoclusters In Polyimide, Mircea Chipara, Tom George, Yingfan Xu, Ralph Skmoski, Lanping Yue, Nasar Ali, David J. Sellmyer
Magnetism Of Fept Nanoclusters In Polyimide, Mircea Chipara, Tom George, Yingfan Xu, Ralph Skmoski, Lanping Yue, Nasar Ali, David J. Sellmyer
David Sellmyer Publications
FePt nanoclusters have been implanted onto polyimide films and subjected to thermal annealing in order to obtain a special magnetic phase (L10) dispersed within the polymer. SQUID measurements quantified the magnetic features of the as-prepared and annealed hybrid films. As-implanted FePt nanoparticles in polyimide films exhibited a blocking temperature of 70 ± 5K. Thermal annealing in zero and 10 kOe applied magnetic field increased the magnetic anisotropy and coercivity of the samples. Wide Angle X-Ray Scattering confirmed the presence of FePt and L10 phase. All samples (as deposited and annealed) exhibited electron spin resonance spectra consisting of two overlapping lines. …
Unusual Spin Correlations In A Nanomagnet, Balamurugan Balasubramanian, Priyanka Manchanda, Ralph Skomski, Pinaki Mukherjee, Bhaskar Das, T A. George, George C. Hadjipanayis, David J. Sellmyer
Unusual Spin Correlations In A Nanomagnet, Balamurugan Balasubramanian, Priyanka Manchanda, Ralph Skomski, Pinaki Mukherjee, Bhaskar Das, T A. George, George C. Hadjipanayis, David J. Sellmyer
David Sellmyer Publications
We show how atomic-scale exchange phenomena can be controlled and exploited in nanoscale itinerant magnets to substantially improve magnetic properties. Cluster-deposition experiments, first-principle simulations, and analytical calculations are used to demonstrate the effect in Co2Si nanoclusters, which have average sizes varying from about 0.6 to 29.5 nm. The cluster-deposited nanoparticles exhibit average magnetic moments of up to 0.70 lB/Co at 10K and 0.49 lB/Co at 300K with appreciable magnetocrystalline anisotropies, in sharp contrast to the nearly vanishing bulk magnetization. The underlying spin correlations and associated cluster-size dependence of the magnetization are explained by a surface induced ferromagnetic spin polarization with …
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 …
Magnetism Of Films, Yi Liu, David J. Sellmyer
Magnetism Of Films, Yi Liu, David J. Sellmyer
David Sellmyer Publications
Films of L10-structure Fe50–xCoxPt50 films are synthesized by co-sputtering Fe, Co, and Pt on (001) MgO substrates and Si substrates with in-situ heating at 830°C. The nanostructures and magnetic properties of the films are characterized by X-ray diffraction, transmission electron microscopy, and SQUID. The compositions of the samples Fe50–xCoxPt50 are designed to maintain an atomic (Fe+Co):Pt ratio of 50:50 while increasing the Co content in each successive sample. In all samples, the X-ray diffraction patterns from samples on MgO substrate exhibit three strong peaks, namely L10Fe50–xCoxPt50 (001), (002), and MgO (002). The X-ray and electron diffraction patterns from …
Structural And Magnetic Properties Of Pr-Alloyed Mnbi Nanostructures, Parashu Kharel, Shah R. Valloppilly, Xingzhong Li, Wenyong Zhang, Ralph Skomski, Jeffrey E. Shield, David J. Sellmyer
Structural And Magnetic Properties Of Pr-Alloyed Mnbi Nanostructures, Parashu Kharel, Shah R. Valloppilly, Xingzhong Li, Wenyong Zhang, Ralph Skomski, Jeffrey E. Shield, David J. Sellmyer
David Sellmyer Publications
The structural and magnetic properties of Pr-alloyed MnBi (short MnBi-Pr) nanostructures with a range of Pr concentrations are investigated. The nanostructures include thin films having Pr concen-trations 0, 2, 3, 5, and 9 at.% and melt-spun ribbons having Pr concentrations 0%, 2%, 4%, and 6%, respectively. Addition of Pr into the MnBi lattice has produced a significant change in the magnetic properties of these nanostructures, including an increase in coercivity and structural phase transition temperature, and a decrease in saturation magnetization and anisotropy energy. The highest value of coercivity measured in the films is 23 kOe and in the ribbons …
Low Temperature Ordering And High (001) Orientation Of [Fe/Pt/Cu]18 Multilayer Films, Yongsheng Yu, Xingzhong Li, T A. George, W D. Fei, Haibo Li, David J. Sellmyer
Low Temperature Ordering And High (001) Orientation Of [Fe/Pt/Cu]18 Multilayer Films, Yongsheng Yu, Xingzhong Li, T A. George, W D. Fei, Haibo Li, David J. Sellmyer
David Sellmyer Publications
[Fe/Pt/Cu]18 multilayer films with different Cu thicknesses were prepared on thermally oxidized Si (111) substrates at room temperature using dc- and rf-magnetron sputtering. The magnetic proper-ties and microstructure of [Fe/Pt/Cu]18 multilayer films annealed at various temperatures have been investigated. Compared with pure [Fe/Pt]18 multilayer films low-temperature ordering and (001) ori-entation in the annealed films with Cu volume concentration below 20% can be obtained. During annealing process Cu atoms diffused into FePt lattice which enhanced the diffusion of Fe and Pt atoms and the grain growth of the films. The perpendicular anisotropy and hard magnetic properties of the …