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University of Nebraska - Lincoln
Materials Research Science and Engineering Center: Faculty Publications
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- Permanent magnets (3)
- Anisotropy (2)
- Permanent magnet (2)
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- Coercivity (1)
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- Discrete domain-wall pinning (1)
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- Inteatomic exchange (1)
- L10 (1)
- L10 magnets (1)
- L10structure (1)
- L1<sub>0</sub> phase (1)
- Magnetic anisotropy (1)
- Magnetic films (1)
- Magnetic moment (1)
- Magnetic recording (1)
- Magnetoresistance (1)
Articles 1 - 30 of 74
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Suppression Of Octahedral Tilts And Associated Changes In Electronic Properties At Epitaxial Oxide Heterostructure Interfaces, A. Y. Borisevich, H. Y. Chang, Mark Huijben, M. P. Oxley, S. Okamoto, Manish K. Niranjan, John D. Burton, Evgeny Y. Tsymbal, Y. H. Chu, P. Yu, R. Ramesh, Sergei V. Kalinin, S. J. Pennycook
Suppression Of Octahedral Tilts And Associated Changes In Electronic Properties At Epitaxial Oxide Heterostructure Interfaces, A. Y. Borisevich, H. Y. Chang, Mark Huijben, M. P. Oxley, S. Okamoto, Manish K. Niranjan, John D. Burton, Evgeny Y. Tsymbal, Y. H. Chu, P. Yu, R. Ramesh, Sergei V. Kalinin, S. J. Pennycook
Materials Research Science and Engineering Center: Faculty Publications
Epitaxial oxide interfaces with broken translational symmetry have emerged as a central paradigm behind the novel behaviors of oxide superlattices. Here, we use scanning transmission electron microscopy to demonstrate a direct, quantitative unit-cell-by-unit-cell mapping of lattice parameters and oxygen octahedral rotations across the BiFeO3 -La0:7 Sr0:3MnO3 interface to elucidate how the change of crystal symmetry is accommodated. Combined with low-loss electron energy loss spectroscopy imaging, we demonstrate a mesoscopic antiferrodistortive phase transition near the interface in BiFeO3 and elucidate associated changes in electronic properties in a thin layer directly adjacent to the interface.
Effect Of Tip Resonances On Tunnelling Anisotropic Magnetoresistance In Ferromagnetic Break Junctions: A First-Principles Study, John D. Burton, Renat F. Sabirianov, Julian P. Velev, O. N. Mryasov, Evgeny Y. Tsymbal
Effect Of Tip Resonances On Tunnelling Anisotropic Magnetoresistance In Ferromagnetic Break Junctions: A First-Principles Study, John D. Burton, Renat F. Sabirianov, Julian P. Velev, O. N. Mryasov, Evgeny Y. Tsymbal
Materials Research Science and Engineering Center: Faculty Publications
First-principles calculations of electron tunneling transport in nanoscale Ni and Co break-junctions reveal strong dependence of the conductance on the magnetization direction, an effect known as tunneling anisotropic magnetoresistance TAMR. An important aspect of this phenomenon stems from resonant states localized in the electrodes near the junction break. The energy and broadening of these states is strongly affected by the magnetization orientation due to spin-orbit coupling, causing TAMR to be sensitive to bias voltage on a scale of a few millivolts. Our results bear a resemblance to recent experimental data and suggest that TAMR driven by resonant states is a …
Quantum Ballistics, Andrei Sokolov
Quantum Ballistics, Andrei Sokolov
Materials Research Science and Engineering Center: Faculty Publications
For the last 40 years, computer-chip manufacturers have been constantly improving the performance of their products by shrinking the size of transistors—the building blocks of processors and memory chips. Having gone from dimensions of a few microns in the early 1970s to 45 nm in Intel’s latest prototypes, the number of transistors that can be etched on a given area of silicon has been doubling every 18 months. This exponential trend, which is known as Moore’s law, has been the driving force behind the relentless miniaturization of microelectronic devices. However, we are now approaching the physical limits of existing technology. …
Magnetization Reversal In Cubic Nanoparticles With Uniaxial Surface Anisotropy, Ralph Skomski, Xiao-Hui Wei, David J. Sellmyer
Magnetization Reversal In Cubic Nanoparticles With Uniaxial Surface Anisotropy, Ralph Skomski, Xiao-Hui Wei, David J. Sellmyer
Materials Research Science and Engineering Center: Faculty Publications
The effect of surface anisotropy on the magnetization reversal in small magnetic particles is investigated. The model considers particles of cubic shape cut from a tetragonal crystal with cube faces in the (001) and equivalent planes. In particles having diameters of less than about 10 nm, the coercivity approaches the Stoner–Wohlfarth limit, but the anisotropy field differs from that of the bulk of the particles. With increasing particle size, the nucleation modes acquire the character of magnetic surface or bulk modes that reduce the coercivity.
Tuning Magnetic Microstructures Of Reference Layer In Magnetic Tunneling Junctions, L. Yuan, Y. S. Lin, Dexin Wang, Sy-Hwang Liou
Tuning Magnetic Microstructures Of Reference Layer In Magnetic Tunneling Junctions, L. Yuan, Y. S. Lin, Dexin Wang, Sy-Hwang Liou
Materials Research Science and Engineering Center: Faculty Publications
Magnetic microstructures in the reference layer in magnetic tunneling junctions (MTJs) are tuned by a reversal field under ambient conditions to investigate their effects on the magnetoresistance (MR) and the exchange coupling field (HE) between the reference layer and the free layer. Magnetization changes in the reference layer can be probed by measuring minor MR loops. The results show the HE of the minor MR loops versus the applied reversal field changes from negative to positive and crosses zero. These results can be explained by the magnetic inhomogeneities at the interface between anti-ferromagnetic/pinned-ferromagnetic layers, which causes the …
Ferromagnetic Multipods Fabricated By Solution Phase Synthesis And Hydrogen Reduction, Y. C. Sui, Y. Zhao, Sitaram S. Jaswal, Xingzhong Li, David J. Sellmyer
Ferromagnetic Multipods Fabricated By Solution Phase Synthesis And Hydrogen Reduction, Y. C. Sui, Y. Zhao, Sitaram S. Jaswal, Xingzhong Li, David J. Sellmyer
Materials Research Science and Engineering Center: Faculty Publications
A simple approach combining pyrolysis and hydrogen reduction is formulated for making ferromagnetic-branched nanostructures called Co multipods. The CoO multipods (branched nanostructures) were produced through the pyrolysis of cobalt-oleate in octadecane at 280 °C with the presence of oleic acid under the protection of pure nitrogen. The angles between the nearest arms are 90°. After the reduction of the branched CoO nanostructures in flowing hydrogen gas in a tubular oven at 290°C, the CoO is reduced to pure cobalt with hexagonal crystal structure and the branched shapes are retained. Anisotropic magnetic properties were found for cobalt multipods on silicon substrates.
Effective Demagnetizing Factors Of Complicated Particle Mixtures, Ralph Skomski, George C. Hadjipanayis, David J. Sellmyer
Effective Demagnetizing Factors Of Complicated Particle Mixtures, Ralph Skomski, George C. Hadjipanayis, David J. Sellmyer
Materials Research Science and Engineering Center: Faculty Publications
Demagnetizing factors have been calculated for hierarchical mixtures and dispersions of magnetic particles, such as columns of platelike particles in a matrix and clusters of spherical particles. The theory involves a number of shape and density parameters describing particles, aggregates, and matrix. It approximates distant particles by a homogeneous medium and yields closed and easy-to-use expressions for the effective demagnetizing factor.
Continuous/Cluster-Pinned Recording Media, Ralph Skomski, M. L. Yan, Yinfan Xu, David J. Sellmyer
Continuous/Cluster-Pinned Recording Media, Ralph Skomski, M. L. Yan, Yinfan Xu, David J. Sellmyer
Materials Research Science and Engineering Center: Faculty Publications
We propose and theoretically investigate a new class of nanostructured magnetic recording films, cluster-pinned recording media. The films consist of magnetic clusters exchange coupled to a continuous hard layer with perpendicular anisotropy and low coercivity. Our calculations yield the coercivity and the cross-track correlation length as a function of film thickness and pinning density and strength. The mechanism is very similar to the Gaunt–Friedel pinning in bulk magnets, which differs from ordinary strong pinning by the selfconsistent dependence of wall curvature and coercivity on defect concentration. The main difference is the exponent for the coercivity as a function of the …
Order-Disorder Transformations In Sm–Co And Sm–Co–Zrc Systems With 2-17 Stoichiometry, Y.Y. Kostogorova-Beller, Jeffrey E. Shield, Matthew J. Kramer
Order-Disorder Transformations In Sm–Co And Sm–Co–Zrc Systems With 2-17 Stoichiometry, Y.Y. Kostogorova-Beller, Jeffrey E. Shield, Matthew J. Kramer
Materials Research Science and Engineering Center: Faculty Publications
This work investigates the order-disorder transformations utilizing time-resolved x-ray diffraction at the Advanced Photon Source. The metastable phases that can form during the order-disorder transformations in the Sm–Co intermetallics have the potential to produce materials with enhanced permanent magnetic properties. The high-temperature experiments transformed the disordered alloys with the TbCu7-type structure obtained by rapid solidification into the mixture of the hexagonal and rhombohedral ordered structures at 1375 K. The ordering process and the role of the ZrC alloying on the phase formation and ordering transformations were examined. The results showed the formation of shoulders of the fundamental peaks …
Demonstration Of An Ultraviolet Zno-Based Optically Pumped Third Order Distributed Feedback Laser, Daniel Hofstetter, Yargo Bonetti, Fabrizio Giorgetta, Abdel-Hamid El-Shaer, Andrey Bakin, Andreas Waag, Rudiger Schmidt-Grund, Mathias Schubert, Marius Grundmann
Demonstration Of An Ultraviolet Zno-Based Optically Pumped Third Order Distributed Feedback Laser, Daniel Hofstetter, Yargo Bonetti, Fabrizio Giorgetta, Abdel-Hamid El-Shaer, Andrey Bakin, Andreas Waag, Rudiger Schmidt-Grund, Mathias Schubert, Marius Grundmann
Materials Research Science and Engineering Center: Faculty Publications
The authors demonstrate an optically pumped ZnO distributed feedback laser operating at 383 nm. For a large temperature range between 10 and 270 K, the device lased in a single longitudinal mode. Mode selection was accomplished via a third order diffraction grating, which was dry etched into a 120 nm thick Si3N4 layer deposited on the ZnO active region. They observed a spectral linewidth of 0.4 nm, a pump threshold intensity of 0.12 MW/cm2, and a peak output power of 14 mW. From wavelength versus temperature measurements, they deduced a temperature tuning coefficient of the …
Creating Micro- And Nanostructures On Tubular And Spherical Surfaces, O. Lima, L. Tan, A. Goel, Mehrdad Negahban, Z. Li
Creating Micro- And Nanostructures On Tubular And Spherical Surfaces, O. Lima, L. Tan, A. Goel, Mehrdad Negahban, Z. Li
Materials Research Science and Engineering Center: Faculty Publications
The authors developed a new technique to create micro- and nanometer scale structures on curved free-standing objects by combining embossing/imprinting lithography approaches with mechanical loadings on elastic films. Embossing/imprinting generates small structures and mechanical loading determines shape or geometry of the final object. As a result, a portion of the tubes with a radius between 0.5 and 3.5 mm and a portion of the spheres with a radius between 2.4 and 7.0 mm were fabricated with grating line features (period of 700 nm) and microlens array features (lens radius of 2.5 µm) atop, respectively. It was found that both static …
Dielectric Constants And Phonon Modes Of Amorphous Hafnium Aluminate Deposited By Metal Organic Chemical Vapor Deposition, C. Bundesmann, O. Buiu, S. Hall, Mathias Schubert
Dielectric Constants And Phonon Modes Of Amorphous Hafnium Aluminate Deposited By Metal Organic Chemical Vapor Deposition, C. Bundesmann, O. Buiu, S. Hall, Mathias Schubert
Materials Research Science and Engineering Center: Faculty Publications
Dielectric constants and long-wavelength optical phonon modes of amorphous hafnium aluminate films with a maximum aluminum content of 19 at. % are studied by infrared spectroscopic ellipsometry (IRSE). The hafnium aluminate films were prepared by metal organic chemical vapor deposition on silicon substrates. IRSE revealed one polar lattice mode and one impurity-type mode, which show all a systematic shift in frequency with varying Al content. The static dielectric constant decreases from 10.1 for 4.6 at. % Al to 8.1 for 19 at. % Al. The absolute values were found to be between 50% and 70% smaller than the values obtained …
Cluster-Assembled Iron-Platinum Nanocomposite Permanent Magnets, Xiangxin Rui, Zhiguang Sun, Yinfan Xu, David J. Sellmyer, Jeffrey E. Shield
Cluster-Assembled Iron-Platinum Nanocomposite Permanent Magnets, Xiangxin Rui, Zhiguang Sun, Yinfan Xu, David J. Sellmyer, Jeffrey E. Shield
Materials Research Science and Engineering Center: Faculty Publications
Exchange-spring nanocomposite permanent magnets have received a great deal of attention for their potential for improved the energy products. Predicted results, however, has been elusive. Optimal properties rely on a uniformly fine nanostructure. Particularly, the soft magnetic phase must be below approximately 10 nm to ensure complete exchange coupling. Inert gas condensation (IGC) is an ideal processing route to produce sub-10 nm clusters method. Two distinct nanostructures have been produced. In the first, Fe clusters were embedded in an FePt matrix by alternate deposition from two sources. Fe cluster content ranged from 0 to 30 volume percent. Post-deposition multi-step heat …
Dielectric Anisotropy And Phonon Modes Of Ordered Indirect-Gap Al0.52In0.48P Studied By Far-Infrared Ellipsometry, Tino Hofmann, V. Gottschalch, Mathias Schubert
Dielectric Anisotropy And Phonon Modes Of Ordered Indirect-Gap Al0.52In0.48P Studied By Far-Infrared Ellipsometry, Tino Hofmann, V. Gottschalch, Mathias Schubert
Materials Research Science and Engineering Center: Faculty Publications
The infrared (100–600 cm−1) optical properties of partially CuPt-type ordered Al0.52In0.48P deposited lattice matched on GaAs are studied by ellipsometry. The authors determine the ordinary and extraordinary dielectric functions and report on the evolution of the optical phonon mode frequencies of Al0.52In0.48P as a function of the degree of ordering. In addition to the InP- and AlP-like phonon modes, they observe two alloy-induced phonon modes which are anisotropic upon CuPt ordering. The observed modes are associated to vibrations with E and A1 symmetries. The alloy-induced phonon modes are useful …
Pairwise Cobalt Doping Of Boron Carbides With Cobaltocene, A. Yu. Ignatov, Yaroslav B. Losovyj, L. Carlson, D. Lagraffe, Jennifer I. Brand, Peter A. Dowben
Pairwise Cobalt Doping Of Boron Carbides With Cobaltocene, A. Yu. Ignatov, Yaroslav B. Losovyj, L. Carlson, D. Lagraffe, Jennifer I. Brand, Peter A. Dowben
Materials Research Science and Engineering Center: Faculty Publications
We have performed Co K-edge x-ray absorption fine structure and x-ray absorption near edge structure measurements of Co-doped plasma enhanced chemical vapor phase deposition (PECVD) grown “C2B10Hx” semiconducting boron carbides, using cobaltocene. Cobalt does not dope PECVD grown boron carbides as a random fragment of the cobaltocene source gas. The Co atoms are fivefold boron coordinated (R=2.10±0.02 Å) and are chemically bonded to the icosahedral cages of B10CHx or B9C2Hy. Pairwise Co doping occurs, with the cobalt atoms favoring sites some 5.28±0.02 …
Electron Effective Mass And Phonon Modes In Gaas Incorporating Boron And Indium, Tino Hofmann, Mathias Schubert, G. Leibiger, V. Gottschalch
Electron Effective Mass And Phonon Modes In Gaas Incorporating Boron And Indium, Tino Hofmann, Mathias Schubert, G. Leibiger, V. Gottschalch
Materials Research Science and Engineering Center: Faculty Publications
The strain-free boron- and indium-containing GaAs compounds are promising candidates for III-V semiconductor solar cell absorber materials with lattice match to GaAs, for which experimental data of the electronic band structure are widely unknown. For nondegenerate, silicon-doped, n-type B0.03In0.06Ga0.91As with band-gap energy of 1.36 eV, determined by near-infrared ellipsometry, a strong increase of the electron effective mass of 44% in B0.03In0.06Ga0.91As compared to In0.06Ga0.94As is obtained from far-infrared magneto-optic generalized ellipsometry studies. The authors thereby obtain the vibrational lattice mode behavior. For BAs, an experimentally obscure compound, the curvature …
Sequential Stretching Lithography, Haojing Lin, Ocelio V. Lima, Li Tan, Zheng Li, Jiangyu Li
Sequential Stretching Lithography, Haojing Lin, Ocelio V. Lima, Li Tan, Zheng Li, Jiangyu Li
Materials Research Science and Engineering Center: Faculty Publications
We developed an embossing/imprinting based nanofabrication technique, dubbed sequential stretching lithography (SSL). In this process, a master pattern is imprinted into an elastomer containing a film of uncured elastomer. The elastomer is cured and then elongated to increase feature density and reduce feature size. Replication of this substrate yields a new master that can be used in further reduction steps. One-dimensional grating features with a pitch size below 200 nm were fabricated from 750 nm-pitch grating lines. This process gives us a faithful pattern miniaturization in all aspects and, as a result, a much effective control on density and dimension …
Nonvolatile Two-Terminal Molecular Memory, Jason Snodgrass, Glen Kennedy, Wai-Ning Mei, Renat F. Sabirianov
Nonvolatile Two-Terminal Molecular Memory, Jason Snodgrass, Glen Kennedy, Wai-Ning Mei, Renat F. Sabirianov
Materials Research Science and Engineering Center: Faculty Publications
We propose a nonvolatile two-terminal memory device with two resistance states based on the molecular tunnel junctions. This tunnel junction is composed of one or a few monolayers of polar molecules sandwiched between two electrodes made of materials with different screening length. As a prototype model system we study a rare earth endohedral metallofullerene molecule with reversible dipole moment sandwiched between metal and semiconducting electrodes, forming a double barrier junction. We use the Thomas-Fermi model to calculate the potential profile across the device. Calculated tunneling conductance through the proposed structure changes by order of magnitude upon the reversal of the …
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.
"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.
Ferroelectric Switch For Spin Injection, Mikhail Ye. Zhuravlev, Sitaram Jaswal, Evgeny Y. Tsymbal, Renat F. Sabirianov
Ferroelectric Switch For Spin Injection, Mikhail Ye. Zhuravlev, Sitaram Jaswal, Evgeny Y. Tsymbal, Renat F. Sabirianov
Materials Research Science and Engineering Center: Faculty Publications
A method for the switching of the spin polarization of the electric current injected into a semiconductor is proposed, based on injecting spins from a diluted magnetic semiconductor through a ferroelectric tunnel barrier. We show that the reversal of the electric polarization of the ferroelectric results in a sizable change in the spin polarization of the injected current, thereby providing a two-state electrical control of this spintronic device. We also predict a possibility of switching of tunneling magnetoresistance in magnetic tunnel junctions with a ferroelectric barrier and coexistence of tunneling magnetoresistance and giant electroresistance effects in these multiferroic tunnel junctions.
Negative Spin Polarization And Large Tunneling Magnetoresistance In Epitaxial Co|Srtio3|Co Magnetic Tunnel Junctions, Julian P. Velev, Kirill D. Belashchenko, Derek A. Stewart, Mark Van Schilfgaarde, Sitaram Jaswal, Evgeny Y. Tsymbal
Negative Spin Polarization And Large Tunneling Magnetoresistance In Epitaxial Co|Srtio3|Co Magnetic Tunnel Junctions, Julian P. Velev, Kirill D. Belashchenko, Derek A. Stewart, Mark Van Schilfgaarde, Sitaram Jaswal, Evgeny Y. Tsymbal
Materials Research Science and Engineering Center: Faculty Publications
We perform an ab initio study of spin-polarized tunneling in epitaxial Co|SrTiO3|Co magnetic tunnel junctions with bcc Co(001) electrodes. We predict a large tunneling magnetoresistance in these junctions, originating from a mismatch in the majority- and minority-spin bands both in bulk bcc Co and at the Co|SrTiO3 interface. The intricate complex band structure of SrTiO3 enables efficient tunneling of the minority d electrons which causes the spin polarization of the Co|SrTiO3 interface to be negative in agreement with experimental data. Our results indicate that epitaxial Co|SrTiO3|Co magnetic tunnel junctions with bcc Co(001) electrodes …