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Full-Text Articles in Physics
Structural Phase Transition And Ferromagnetism In Monodisperse 3 Nm Fept Particles, Chuan-Bing Rong, Narayan Poudyal, Girija S. Chaubey, Vikas Nandwana, Ralph Skomski, Y. Q. Wu, Matthew J. Kramer, J. Ping Liu
Structural Phase Transition And Ferromagnetism In Monodisperse 3 Nm Fept Particles, Chuan-Bing Rong, Narayan Poudyal, Girija S. Chaubey, Vikas Nandwana, Ralph Skomski, Y. Q. Wu, Matthew J. Kramer, J. Ping Liu
Ralph Skomski Publications
FePt nanoparticles with a size of 3 nm and thermally stable room-temperature ferromagnetism are investigated. The monodisperse nanoparticles were prepared by chemical synthesis and a salt-matrix annealing technique. Structural and magnetic characterizations confirmed the phase transition from the disordered face-centered cubic structure to the L10 structure with the chemical ordering parameter of 0.62±0.05. Analysis in blocking temperature and fitting of temperature dependence of switching field reveals that the transformed 3 nm nanoparticles have a magnetic anisotropy constant of (2.8±0.2) x 106 J/m3, smaller than those for the bigger particles and the fully ordered L1 …
Finite-Temperature Depolarization In Half Metals, Ralph Skomski
Finite-Temperature Depolarization In Half Metals, Ralph Skomski
Ralph Skomski Publications
The temperature dependence of the spin polarization of type-I half-metallic ferromagnets is investigated and compared with that of other magnetic materials, such as semimetals, strong and weak ferromagnets, and exchange-enhanced Pauli paramagnets. Stable atomic moments, as realized by strong intra-atomic exchange, exhibit a nonzero spin-down density of states (DOS) at finite temperatures. This thermal spin mixing means that the conductivity of the “insulating” spin channel is always nonzero and that half-metallic ferromagnetism is an idealized limit. At zero temperature, similar effects are caused by intersublattice interactions, spin–orbit coupling and crystal imperfections. With increasing interatomic hopping, the moment becomes unstable, and …
Phase Formation In L1 0 Magnets, Ralph Skomski
Phase Formation In L1 0 Magnets, Ralph Skomski
Ralph Skomski Publications
Structural and magnetic properties of substituted L10 compounds are investigated. Focus is on L10 structures of the general type ABC2, where each second layer of the original structure is replaced by a checkerboard of A and B atoms. At low temperatures, L10 compounds with ABC2 stoichiometry will segregate into AC and AB L10 phases, forming an ordered ABC2 compound or exhibit a transition into a more complicated structure. The ordering has a strong impact on the magnetism of the alloys, especially on the anisotropy. The hypothetical new ternary …
Role Of Thermodynamic Fluctuations In Magnetic Recording (Invited), Ralph Skomski
Role Of Thermodynamic Fluctuations In Magnetic Recording (Invited), Ralph Skomski
Ralph Skomski Publications
The thermal stability of the information stored in magnetic recording media is determined by a complex hierarchy. The leading consideration is the static or zero-temperature magnetization reversal complemented by the intrinsic temperature dependence of the micromagnetic parameters. Thermally activated Arrhenius (or Néel-Brown) processes modify the reversal by realizing paths close to static reversal, whereas “giant fluctuations” corresponding to reversal fields much higher than the nucleation field can safely be excluded. Thermally activated reversal in very thin elongated nanoparticles limits the thermal stability of magnetic recording media but degenerates into coherent rotation as the temperature is lowered, thereby reconciling micromagnetism and …
Magnetic Impurities In Magic-Number Clusters, Ralph Skomski, David J. Sellmyer
Magnetic Impurities In Magic-Number Clusters, Ralph Skomski, David J. Sellmyer
Ralph Skomski Publications
It is investigated how magnetic impurities modify the behavior of metallic clusters. Two complementary models are used, an s-d exchange model with a stable magnetic moment and a Hubbard-type Kondo model. The s-d and s-f interactions are modeled by a pointlike potential, as in the Ruderman-Kittel-Kasuya-Yosida approximation, but the perturbed levels are obtained by diagonalizing the interaction matrix rather than using perturbation theory. The spin polarization of the conduction electrons due to the magnetic impurities leads to a reduction of the highest occupied molecular orbital–lowest unoccupied molecular orbital splitting. A particularly interesting case is …
Coupled Precession Modes In Indirect Exchange-Coupled [Pt/Co]–Co Thin Films, Steven A. Michalski, Jian Zhou, Ralph Skomski, Roger D. Kirby
Coupled Precession Modes In Indirect Exchange-Coupled [Pt/Co]–Co Thin Films, Steven A. Michalski, Jian Zhou, Ralph Skomski, Roger D. Kirby
Ralph Skomski Publications
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