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Full-Text Articles in Physics

Unusual Perpendicular Anisotropy In Co2Tisi Films, Yunlong Jin, Shah R. Valloppilly, Parashu R. Kharel, Rohit Pathak, Arti Kashyap, Ralph Skomski, David J. Sellmyer Jan 2019

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 m3. This result is surprising for several reasons. First, surface and interface anisotropies are too small to explain perpendicular anisotropy in such rather thick films. Second, Co ...


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 Jan 2015

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 ...


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 Jan 2015

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 ...


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 Jan 2015

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 ...


Synthesis And Magnetism Of Single-Phase Mn-Ga Films, Wenyong Zhang, Parashu Kharel, Shah R. Valloppilly, Ralph A. Skomski, David J. Sellmyer Jan 2015

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 ...


Novel Structures And Physics Of Nanomagnets (Invited), David J. Sellmyer, Balamurugan Balamurugan, Bhaskar Das, P Murherjee, Ralph A. Skomski, George C. Hadjipanayis Jan 2015

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 ...


Magnetism Of Fept Nanoclusters In Polyimide, Mircea Chipara, Tom George, Yingfan Xu, Ralph Skmoski, Lanping Yue, Nasar Ali, David J. Sellmyer Jan 2015

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. The ...


Magnetism Of Ta Dichalcogenide Monolayers Tuned By Strain And Hydrogenation, Priyanka Manchanda, Vinit Sharma, Hongbin Yu, David J. Sellmyer, Ralph A. Skomski Jan 2015

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 ...


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 Jan 2014

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 ...


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 Jan 2014

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 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 Jan 2014

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 ...


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 Jan 2014

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 ...


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 Jan 2014

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 ...


Magnetic Silicon Nanoparticles, Priyanka Manchanda, Pankaj Kumar, Balamurugan Balasubramanian, Pinaki Mukherjee, Arti Kashyap, David J. Sellmyer, Ralph Skomski Jan 2014

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 ...


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 Jan 2014

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 ...


Hf–Co And Zr–Co Alloys For Rare-Earth-Free Permanent Magnets, Balamurugan Balasubramanian, Bhaskar Das, Wenyong Zhang, Ralph Skomski, David J. Sellmyer Jan 2014

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 energy products ...


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 Jan 2014

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 ...


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 Jan 2014

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 ...


Kondorski Reversal In Magnetic Nanowires, Ralph A. Skomski, Eva Schubert, Axel Enders, David J. Sellmyer Jan 2014

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.


Orthorhombic Zr2Co11 Phase Revisited, Xingzhong Li, Wenyong Zhang, David J. Sellmyer, X Zhao, M C. Nguyen, C Z. Wang, K M. Ho Jan 2014

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 Jan 2014

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 Jan 2014

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 ...


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 Jan 2014

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 ...


Effect Of Annealing On Nanostructure And Magnetic Properties Of Zr2Co11 Material, Wenyong Zhang, Xingzhong Li, Shah R. Valloppilly, Ralph A. Skomski, David J. Sellmyer Jan 2014

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 ...


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 Jan 2014

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 ...


Direct Chemical Synthesis Of L10-Feptau Nanoparticles With High Coercivity, Yongsheng Yu, Pinaki Mukherjee, Yuan Tian, Xingzhong Li, David J. Sellmyer Jan 2014

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 ...


Effect Of Exchange Interactions On The Coercivity Of Smco5 Nanoparticles Made By Cluster Beam Deposition, O Akdogan, W Li, B Balasubrmanian, David J. Sellmyer, George C. Hadjipanayis Jan 2013

Effect Of Exchange Interactions On The Coercivity Of Smco5 Nanoparticles Made By Cluster Beam Deposition, O Akdogan, W Li, B Balasubrmanian, David J. Sellmyer, George C. Hadjipanayis

David Sellmyer Publications

Single crystal SmCo5 nanoparticles with an average size of 3.5 nm are produced by cluster-beam deposition. When deposited without matrix, the nanoparticles showed a super-paramagnetic be-havior with a blocking temperature of 145 K. Dispersion of the SmCo5 nanoparticles in a carbon matrix results in an increase in both the coercivity and the blocking temperature. Room temperature coercivities as high as 12 kOe are obtained for the first time in mono-layers of SmCo5 nanoparticles dispersed in C matrix. δM plots show that the interactions in the samples are of exchange type, which can decrease the overall ...


Novel Nanostructured Rare-Earth-Free Magnetic Materials With High Energy Products, Balamurugan Balasubramanian, Bhaskar Das, Ralph Skomski, Wenyong Zhang, David J. Sellmyer Jan 2013

Novel Nanostructured Rare-Earth-Free Magnetic Materials With High Energy Products, Balamurugan Balasubramanian, Bhaskar Das, Ralph Skomski, Wenyong Zhang, David J. Sellmyer

David Sellmyer Publications

The development of new iron- or cobalt-rich permanent-magnet materials is of paramount importance in materials science and technology since high-performance materials based on Nd2Fe14B or FePt are extremely expensive or subject to limited rare-earth supplies.[1–4] Aside from phase-diagram considerations, this requires alloys with high magnetocrystal-line anisotropy K1 and Curie temperature Tc. However, the range of alternative compounds with appreciable K1 and high Tc is limited, and the situation is often aggravated by their metastable nature and by the requirement of high-formation temperatures.[5–12] For exam-ple, two suitable candidates are Zr2Co11 ...


Solubility Extension And Phase Formation In Gas-Condensed Co–W Nanoclusters, Farhad Golkar, Matthew J. Kramer, Ames Laboratory, Ralph A. Skomski, David J. Sellmyer, Jeffrey E. Shield Jan 2013

Solubility Extension And Phase Formation In Gas-Condensed Co–W Nanoclusters, Farhad Golkar, Matthew J. Kramer, Ames Laboratory, Ralph A. Skomski, David J. Sellmyer, Jeffrey E. Shield

David Sellmyer Publications

Co–W alloy clusters with extended solubility of W in hcp Co were produced by inert-gas condensa-tion. The structural state of the as-deposited Co–W clusters was found to be critically dependent on processing parameters such as the cooling scheme and sputtering power. For the water-cooled clus-ters, the mean size and percent crystalline were strongly dependent on sputtering power, while the percent crystalline of the liquid nitrogen-cooled clusters was not as affected by the sputtering power. At low sputtering powers, the water-cooled clusters were predominantly amorphous, but became increasingly more crystalline as the sputtering power increased. The predominant crystalline phase ...


Magnetism Of Rapidly Quenched Rhombohedral Zr2Co11-Based Nanocomposites, Wenyong Zhang, Xingzhong Li, Shah R. Valloppilly, Ralph A. Skomski, Jeffrey E. Shield, David J. Sellmyer Jan 2013

Magnetism Of Rapidly Quenched Rhombohedral Zr2Co11-Based Nanocomposites, Wenyong Zhang, Xingzhong Li, Shah R. Valloppilly, Ralph A. Skomski, Jeffrey E. Shield, David J. Sellmyer

David Sellmyer Publications

The effect of quench rate and Zr content on nanostructure and magnetic properties of melt-spun ZrxCo100−x (x = 16–21) is investigated. High quench rate favors the formation of rhombohedral Zr2Co11, which is the hard phase. The coercivity increases with an increase in quench rate. Zr addition in limited amounts decreases the grain size of magnetic phases, which may promote the effective ex-change coupling of soft magnetic phases. Therefore, coercivity and maximum energy product of Zr2Co11-based materials are significantly enhanced. The best magnetic properties, iHc = 3.0 kOe and (BH ...