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Full-Text Articles in Physical Sciences and Mathematics
Fundamental And Magnetic-Hardening Studies Of Rare-Earth And Nanocomposite Magnets, David J. Sellmyer, George C. Hadjipanayis
Fundamental And Magnetic-Hardening Studies Of Rare-Earth And Nanocomposite Magnets, David J. Sellmyer, George C. Hadjipanayis
David Sellmyer Publications
In this project we study new nanocrystalline and nanocomposite structures that have high potential for permanent-magnet development. These materials, which can be synthesized to have either very high or intermediate coercivities, have many applications in electric power, transportation, and information-storage industries. There is great interest in further development of understanding and application of these materials. Following are brief discussions of recent research highlights for the present grant.
Nanocomposite (Nd,Dy)(Fe,Co,Nb,B) 5.5/Α-Fe Multilayer Magnets With High Performance, W. Liu, Z.D. Zhang, J. Ping Liu
Nanocomposite (Nd,Dy)(Fe,Co,Nb,B) 5.5/Α-Fe Multilayer Magnets With High Performance, W. Liu, Z.D. Zhang, J. Ping Liu
David Sellmyer Publications
The structural and magnetic properties of rare-earth nanocomposite magnets of a (Nd,Dy)(Fe,Co,Nb,B) 5.5 single layer and a (Nd,Dy)(Fe,Co,Nb,B) 5.5/α-Fe multilayer prepared by sputtering and heat treatment have been investigated. Incomplete exchange coupling behaviour is observed in the Ti-buffered NdDyFeCoNbB + 40 wt%Fe single layer magnet. After annealing, the laminated nanostructure consisting of mutually dispersed soft and hard phases results in remanence enhancement. The optimum magnetic properties of Jr= 1.11 T, μ0i Hc = 0.88 T and (BH)max = 192 kJ m-3 are achieved in the multilayer magnet annealed at 550°C for 30 min. …
Highly Oriented Nonepitaxially Grown L10 Fept Films, M.L. Yan, Nathan D. Powers, David J. Sellmyer
Highly Oriented Nonepitaxially Grown L10 Fept Films, M.L. Yan, Nathan D. Powers, David J. Sellmyer
David Sellmyer Publications
A method of preparing nonepitaxially grown, highly textured L10 FePt thin films is described. A nearly perfect (001) texture was obtained by direct deposition of FePt films on Corning 7059 glass substrates and subsequent rapid thermal annealing. The ordering and orientation of the L10-phase FePt grains were controlled by the initial as-deposited film structure, and also by the annealing process. Magnetic measurements reveal large perpendicular anisotropy for these (001) textured films. The substrates and processes used for nonepitaxial growth of L10 ordered FePt films are much more compatible with practical applications than those …
Studies Of Magnetic Properties Of The Stabilizing Layer For Synthetic Antiferromagnetically Coupled Media, Z.S. Shan, L. Bitman, S.S. Malhotra, D. Stafford, B. Bian, G. Bertero
Studies Of Magnetic Properties Of The Stabilizing Layer For Synthetic Antiferromagnetically Coupled Media, Z.S. Shan, L. Bitman, S.S. Malhotra, D. Stafford, B. Bian, G. Bertero
David Sellmyer Publications
The effects of the stabilizing layer thickness and its temperature dependence on the magnetic properties were investigated experimentally. These results were used to analyze the magnetic structure of the thin stabilizing layer and its effect on the coupling strength, which is valuable for improving the design of synthetic antiferromagnetically coupled media.
Structure And Magnetic Properties Of Sputtered Hard/Soft Multilayer Magnets, W. Liu, Z.D. Zhang, J. Ping Liu, B.Z. Cui, X.K. Sun, J. Zhou, David J. Sellmyer
Structure And Magnetic Properties Of Sputtered Hard/Soft Multilayer Magnets, W. Liu, Z.D. Zhang, J. Ping Liu, B.Z. Cui, X.K. Sun, J. Zhou, David J. Sellmyer
David Sellmyer Publications
The films with HM = (Pr,Dy)(Fe,Co,Nb,B) 5.5 and SM=Fe, FeCo were prepared by sputtering and subsequent heat treatment. The coercivity of Ti-buffered (Pr,Dy)(Fe,Co,Nb,B) 5.5 single-layer film with 320 nm thickness is as large as 18.8 kOe at room temperature. X-ray diffraction results reveal that the Pr2Fe14B-type phase is randomly oriented in almost all the multilayer films. For the multilayers of Ti(30 nm)/[HM(16 nm)Fe(x nm)]×20/Ti(30 nm)/Si(substrate), the remanence increases and the coercivity decreases with the addition of Fe content, in comparison with the results of the single-layer film and the maximum energy product of 14.8 MGOe is …
Exchange Through Nonmagnetic Insulating Matrix, Ralph Skomski, Arti Kashyap, Y. Quiang, David J. Sellmyer
Exchange Through Nonmagnetic Insulating Matrix, Ralph Skomski, Arti Kashyap, Y. Quiang, David J. Sellmyer
David Sellmyer Publications
Exchange interactions between hard-magnetic particles in a nonmagnetic matrix are investigated by model calculations. A Landau–Ginzburg approach is developed to describe the net exchange interactions between spheres of arbitrary diameters. Introducing cylindrical coordinates and integrating over the surfaces of the adjacent spheres yields an exchange coupling which decreases with a decay length depending on interatomic exchange, intra-atomic exchange, and temperature. Typically, the decay length does not exceed a few interatomic distances. The decay is exponential but also contains a prefactor depending on the surface curvature of the grains. It increases with decreasing curvature, but this dependence is only a small …
Copt Hard Magnetic Nanoparticle Films Synthesized By High Temperature Chemical Reduction, Yucheng Sui, Lanping Yue, Ralph Skomski, Xingzhong Li, J. Zhou, David J. Sellmyer
Copt Hard Magnetic Nanoparticle Films Synthesized By High Temperature Chemical Reduction, Yucheng Sui, Lanping Yue, Ralph Skomski, Xingzhong Li, J. Zhou, David J. Sellmyer
David Sellmyer Publications
The synthesis of hard-magnetic CoPt nanoparticle films by hydrogen reduction of Co nitride and Pt chloride mixture is reported. Thin porous alumina films are adopted as the carrier of the initial aqueous solution and of the final reducing products of CoPt nanoparticles. It is found that chemical ordering of L0–CoPt occurs above 400 °C. Partial phase transformation occurs in the alumina substrate when the treatment temperature is higher than 600 °C. The film coercivity increases with increasing annealing temperature and reaches a maximum value of 24.2 kOe when the reduction is carried out at 700 °C for 2 …
Magnetic Hysteresis Of Mechanically Alloyed Sm–Co Nanocrystalline Powders, J. Zhou, Ralph Skomski, David J. Sellmyer
Magnetic Hysteresis Of Mechanically Alloyed Sm–Co Nanocrystalline Powders, J. Zhou, Ralph Skomski, David J. Sellmyer
David Sellmyer Publications
Mechanically alloyed Sm–Co powders and Sm12 (Co,Cu,Ti) 88 powders are investigated. X-ray diffraction patterns show that after annealing, structures of 2:7, 1:5, and 1:7 phases form. A room-temperature coercivity of 41 kOe was obtained in Sm2Co7 powders. Magnetic hysteresis was investigated by the method of δ m curves. Positive value δ m curves were obtained in Sm2Co7 and SmCo5, while negative values were found in SmCo7.3 and SmCo8 indicating different magnetization reversal mechanisms. Nanocrystalline powders of Sm12 (Co,Cu,Ti) 88 with a mixture of 1:5 and 2:17 phases form …
Spin Structure At Nanojunctions And Constrictions, Ralph Skomski, David J. Sellmyer
Spin Structure At Nanojunctions And Constrictions, Ralph Skomski, David J. Sellmyer
David Sellmyer Publications
A micromagnetic Green-function approach is used to investigate the effect of nanojunctions, constraints, and other obstacles on spin-dependent conduction. Depending on geometry, the determination of the spin structure involves several types of Bessel functions. A common feature of the Green functions is the involvement of the domain-wall width of the main phase, which can be interpreted as the decay length of the magnetization perturbation away from the junction. This length is typically on the order of 10 nm and independent of the strength of the perturbation. Only the magnitude of the magnetization perturbation depends on the strength of the inhomogenity. …
Magnetic Properties Of L10 Fept And Fept:Ag Nanocluster Films, Yinfan Xu, Zhiguang Sun, Y. Qiang, David J. Sellmyer
Magnetic Properties Of L10 Fept And Fept:Ag Nanocluster Films, Yinfan Xu, Zhiguang Sun, Y. Qiang, David J. Sellmyer
David Sellmyer Publications
A sputtering gas-aggregation technique has been used to prepare FePt and FePt:Ag nanocluster films. The cluster size was controlled in a range from 3 to 6 nm. FePt cluster films were directly deposited onto Si substrate; FePt:Ag cluster films were fabricated by depositing a FePt cluster layer between a Ag underlayer and overlayer. Nanostructure and magnetic properties of the samples were characterized by x-ray diffraction, transmission electron microscopy, and magnetometry. The high magnetic anisotropy L10 fct phase was realized in the films annealed at a temperature of 550 °C and above. The orientation of clusters is random. The …
Effects Of Rapid Thermal Annealing On Nanostructure, Texture And Magnetic Properties Of Granular Fept:Ag Films For Perpendicular Recording (Invited), Y. Shao, M.L. Yan, David J. Sellmyer
Effects Of Rapid Thermal Annealing On Nanostructure, Texture And Magnetic Properties Of Granular Fept:Ag Films For Perpendicular Recording (Invited), Y. Shao, M.L. Yan, David J. Sellmyer
David Sellmyer Publications
We report effects of rapid thermal annealing on nanostructure, texture, and magnetic properties of granular FePt:Ag films. It was found that the orientations of FePt grains were dependent strongly on the as-deposited multilayer structure and the annealing processes. Through the control of the annealing processes, (001) textured L10 granular FePt:Ag films were obtained. Magnetic measurements revealed that saturation magnetization Ms, perpendicular coercivity Hc, and remanence ratio Mr/Ms, were also dependent on the annealing temperature, annealing time and Ag content. Perpendicular Hc values increased from 1.5 to 15 kOe …
Spin-Wave Modes In Magnetic Nanowires, Ralph Skomski, M. Chipara, David J. Sellmyer
Spin-Wave Modes In Magnetic Nanowires, Ralph Skomski, M. Chipara, David J. Sellmyer
David Sellmyer Publications
Spin-wave modes in magnetic transition-metal nanowires having diameters of about 10 nm and lengths on the order of 1 µm are investigated by model calculations. There are quasicontinuous modes with k vectors parallel to the wires axis and discrete modes with k vectors perpendicular to the wire axis. Due to the small cross section of the wires, the perpendicular modes can be ignored in many cases and the low-temperature behavior of the wires is quasi one-dimensional. Using an analytic approach and exploiting the analogy between micromagnetism and quantum mechanics it is shown that all spin-wave modes with k vectors parallel …