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Evidence Of Long-Wavelength Collective Excitations In Magnetic Superlattices, Nikolay I. Polushkin, Steven A. Michalski, Lanping Yue, Roger D. Kirby
Evidence Of Long-Wavelength Collective Excitations In Magnetic Superlattices, Nikolay I. Polushkin, Steven A. Michalski, Lanping Yue, Roger D. Kirby
Materials Research Science and Engineering Center: Faculty Publications
We report on a mechanism of dynamic dipolar coupling in magnetic superlattices via long-wavelength nonevanescent fields. In the spin excitation spectra of our heterophase stripe structures, such interactions mediate a singlet ↔ doublet crossover in the frequency regime driven by the orientation of an external static field. This crossover is a new feature observed in collective behavior of superlattices, though there is some analogy of this phenomenon with birefringence taking place in optical superlattices. We envision applying the collective effects described here in microwave photonic devices.
Solution Chemistry Control To Make Well Defined Submicron Continuous Fibres By Electrospinning: The (Ch3ch2ch2o)4ti/Acoh/Poly(N-Vinylpyrrolidone) System, Gustavo F. Larsen, Maciej Skotak
Solution Chemistry Control To Make Well Defined Submicron Continuous Fibres By Electrospinning: The (Ch3ch2ch2o)4ti/Acoh/Poly(N-Vinylpyrrolidone) System, Gustavo F. Larsen, Maciej Skotak
Papers in Materials Science
The (CH3CH2CH2O)4Ti/AcOH/poly(N-vinylpyrrolidone) system has been shown to yield suitable formulations for electrohydrodynamic (EHD) processing into continuous fibres and particles. The EHD processability of this, and generally most sol–gel-based formulations, into well defined fibres and particles with narrow submicron-range diameter distributions depends not only on the EHD process variables (electric field and flow rates), but also on the stability of key physical properties (e.g., conductivity, viscosity, surface tension, density and dielectric constant) of the sol over time. Sols that were almost certainly still undergoing hydrolysis and condensation reactions have been processed via EHD by many research groups to make materials with …
"Introduction" To Advanced Magnetic Nanostructures, David J. Sellmyer, Ralph Skomski
"Introduction" To Advanced Magnetic Nanostructures, David J. Sellmyer, Ralph Skomski
Materials Research Science and Engineering Center: Faculty Publications
The nanostructures considered here are magnetic and characterized by structural length scales ranging from a few interatomic distances to about one micrometer. The basic length unit is the nanometer (1 nm = 10–3 μm = 10–9 m), corresponding to about four interatomic Fe-Fe distances. Magnetic nanostructures pose experimental challenges, exhibit interesting physical phenomena, and have many present or potential applications. An important aspect is that structural lengths affect, but only partly determine, the magnetic length scales encountered in the structures. Examples are domains in semihard nanoparticles, where both the domain size and the domain-wall thickness may be smaller …
A Measurement Of Electron-Wall Interactions Using Transmission Diffraction From Nanofabricated Gratings, Brett E. Barwick, Glen Gronniger, Lu Yuan, Sy-Hwang Liou, Herman Batelaan
A Measurement Of Electron-Wall Interactions Using Transmission Diffraction From Nanofabricated Gratings, Brett E. Barwick, Glen Gronniger, Lu Yuan, Sy-Hwang Liou, Herman Batelaan
Materials Research Science and Engineering Center: Faculty Publications
Electron diffraction from metal coated freestanding nanofabricated gratings is presented, with a quantitative path integral analysis of the electron-grating interactions. Electron diffraction out to the 20th order was observed indicating the high quality of our nanofabricated gratings. The electron beam is collimated to its diffraction limit with ion-milled material slits. Our path integral analysis is first tested against single slit electron diffraction, and then further expanded with the same theoretical approach to describe grating diffraction. Rotation of the grating with respect to the incident electron beam varies the effective distance between the electron and grating bars. This allows the measurement …
Effects Of Ion-Beam Irradiation On The L10 Phase Transformation And Their Magnetic Properties Of Fept And Ptmn Films (Invited), Chih-Huang Lai, Sheng-Huang Huang, Cheng-Han Yang, C.C. Chiang, Sy_Hwang Liou, David J. Sellmyer, M. L. Yan, L. Yuan, T. Yokata
Effects Of Ion-Beam Irradiation On The L10 Phase Transformation And Their Magnetic Properties Of Fept And Ptmn Films (Invited), Chih-Huang Lai, Sheng-Huang Huang, Cheng-Han Yang, C.C. Chiang, Sy_Hwang Liou, David J. Sellmyer, M. L. Yan, L. Yuan, T. Yokata
Materials Research Science and Engineering Center: Faculty Publications
In this paper, we illustrate how to modify the structure and magnetic properties of L10 FePt and PtMn films using ion-beam irradiation. Highly ordered L10 FePt and PtMn phases were achieved directly by using 2 MeV He-ion irradiation without conventional post-annealing. A high ion-beam current density (~μA/cm2 ) was used to achieve direct beam heating on samples. This irradiation-induced heating process provides efficient microscopic energy transfer and creates excess point defects, which significantly enhances the diffusion and promotes the formation of the ordered L10 phase. In-plane coercivity of FePt films greater than 5700 Oe could be …
Spin-Polarized Electronic Structure, Arti Kashyap, Renat F. Sabirianov, Sitaram Jaswal
Spin-Polarized Electronic Structure, Arti Kashyap, Renat F. Sabirianov, Sitaram Jaswal
Materials Research Science and Engineering Center: Faculty Publications
This chapter is devoted to the electronic structure of nanoscale metallic magnets. After an introduction to methods of electronic structure calculations, we review how recent trends translate into the description of magnetic nanostructures. Among the considered structures are nanowires, small particles, surfaces and interfaces, and multilayers, and emphasis is on magnetic properties such as moment and magnetization, interatomic exchange, and anisotropy.
One of the goals of computational nanoscience is to calculate physical and chemical properties from first principles. This requires the knowledge of the electronic structures of the materials system in question. The density-functional theory (DFT) makes a huge step …
Nanobiomagnetics, Diandra Leslie-Pelecky, V. Labhasetwar, R. H. Kraus Jr.
Nanobiomagnetics, Diandra Leslie-Pelecky, V. Labhasetwar, R. H. Kraus Jr.
Materials Research Science and Engineering Center: Faculty Publications
The application of nanomagnetic materials to biological systems has produced significant advances in research, diagnosis, and treatment of numerous pathologies. This chapter summarizes the major applications of magnetic materials: magnetic targeting, drug and gene delivery, magnetic separation, the use of magnetic beads in manipulating single molecules, as contrast agents in magnetic resonance imaging, and for hyperthermia. Biocompatibility requirements for magnetic materials used in these applications are reviewed.
“Nanobiomagnetism” is the intersection of nanomagnetism and medicine that focuses on biological systems and/or processes. Magnetism is an inherent facet of life, from iron in blood to the ability of magnetotactic bacteria, birds, …
Understanding And Control Of Lateral Contraction In Stamping Lithography, Zheng Li, Li Tan, Gang-Yu Liu
Understanding And Control Of Lateral Contraction In Stamping Lithography, Zheng Li, Li Tan, Gang-Yu Liu
Materials Research Science and Engineering Center: Faculty Publications
Thin film contraction under external mechanical stress can be used to miniaturize size and increase density of patterned features on top. Nonlinear Finite Element Analysis is used to provide guidance on this contraction process. It was found that the substrate contraction causes stress accumulation along interfaces between protruded features and substrate. These stress accumulation complexes the control of profile changes on patterned features and suggest a design of patterned features arranged beyond a critical distance to avoid cross-interference.
Fast And Slow Magnetization Processes In Magnetic Recording Media, Jian Zhou, Ralph Skomski, Steven A. Michalski, Roger D. Kirby, David J. Sellmyer
Fast And Slow Magnetization Processes In Magnetic Recording Media, Jian Zhou, Ralph Skomski, Steven A. Michalski, Roger D. Kirby, David J. Sellmyer
Materials Research Science and Engineering Center: Faculty Publications
Information loss due to thermal activation is a major concern in ultrahigh-density magnetic recording media. The usually considered mechanism is thermally activated magnetization reversal over micromagnetic energy barriers. However, micromagnetic approaches ignore local anisotropy fluctuations, which translate into a time-dependent reduction of the remanent magnetization. The effect is negligibly small in macroscopic magnets but becomes important on a scale of a few nanometers.
Magnetic Aging, Ralph Skomski, Jian Zhou, Roger D. Kirby, David J. Sellmyer
Magnetic Aging, Ralph Skomski, Jian Zhou, Roger D. Kirby, David J. Sellmyer
Materials Research Science and Engineering Center: Faculty Publications
Thermally activated magnetization reversal is of great importance in areas such as permanent magnetism and magnetic recording. In spite of many decades of scientific research, the phenomenon of slow magnetization dynamics has remained partially controversial. It is now well-established that the main mechanism is thermally activated magnetization reversal, as contrasted to eddy currents and structural aging, but the identification of the involved energy barriers remains a challenge for many systems. Thermally activated slow magnetization processes proceed over energy barriers whose structure is determined by the micromagnetic free energy. This restricts the range of physically meaningful energy barriers. An analysis of …
Surface Segregation In Multicomponent Clusters, Peter A. Dowben, Ning Wu, Natalie Palina, H. Modrow, R. Müller, J. Hormes, Yaroslav B. Losovyj
Surface Segregation In Multicomponent Clusters, Peter A. Dowben, Ning Wu, Natalie Palina, H. Modrow, R. Müller, J. Hormes, Yaroslav B. Losovyj
Materials Research Science and Engineering Center: Faculty Publications
Nanostructured materials are not immune from surface segregation, as can be shown for solid samples made from nanosized BaFe12-2xCoxTixO19 barium ferrite particles and a variety of free clusters. Both theory and experiment provide ample demonstration that very limited dimensions of very small clusters does not necessarily impart stability against surface and grain boundary segregation. In fact, with the larger surface to volume ratio in small clusters and lower average atomic coordination, we anticipate that compositional instabilities in small clusters will readily occur.