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List Of Publications (Through June 2006): Roger Kirby, Roger D. Kirby Jul 2006

List Of Publications (Through June 2006): Roger Kirby, Roger D. Kirby

Roger Kirby Publications

Chronological list of 76 articles and 90 abstracts & proceedings publications by Roger Kirby, Department of Physics and Astronomy, University of Nebraska-Lincoln.


Formation Of An Anisotropy Lattice In Co/Pt Multilayers By Direct Laser Interference Patterning, Aliekber Aktag, Steven A. Michalski, Lanping Yue, Roger D. Kirby, Sy_Hwang Liou May 2006

Formation Of An Anisotropy Lattice In Co/Pt Multilayers By Direct Laser Interference Patterning, Aliekber Aktag, Steven A. Michalski, Lanping Yue, Roger D. Kirby, Sy_Hwang Liou

Roger Kirby Publications

We report on the use of direct laser interference patterning to form an “anisotropy” lattice in Co/Pt thin film multilayers. Co/Pt multilayers have been extensively studied and, for the compositions studied here, are characterized by strong perpendicular magnetic anisotropy in which the magnetic moment is perpendicular to the film plane. In direct laser interference patterning, two-to-four coherent laser beams from a pulsed Nd:YAG laser strike the sample surface simultaneously, and for sufficiently intense beams the sample properties are modified locally where interference maxima occur. Kerr rotation, magnetic force microscopy, and atomic force microscopy measurements after patterning by ...


Micromagnetic Energy Barriers, Ralph Skomski, Jian Zhou, Roger D. Kirby, David J. Sellmyer Apr 2006

Micromagnetic Energy Barriers, Ralph Skomski, Jian Zhou, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

The structure of micromagnetic energy barriers responsible for slow magnetization processes is investigated. 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 the underlying micromagnetic free energy yields power-law dependences with exponents of 3/2 or 2 for physically reasonable models. This must be contrasted to other power laws, such as linear laws, and to 1/H-type dependences. In the limit of small energy barriers, corrections to the Arrhenius law become important. In this regime, there is no ...


Geometry And Magnetism Of L10 Nanostructures, Kory D. Sorge, Ralph Skomski, Maria Daniil, Steven A. Michalski, L. Gao, Jian Zhou, M. Yan, Yucheng Sui, Roger D. Kirby, Sy_Hwang Liou, David J. Sellmyer Aug 2005

Geometry And Magnetism Of L10 Nanostructures, Kory D. Sorge, Ralph Skomski, Maria Daniil, Steven A. Michalski, L. Gao, Jian Zhou, M. Yan, Yucheng Sui, Roger D. Kirby, Sy_Hwang Liou, David J. Sellmyer

Roger Kirby Publications

The fabrication and magnetism of L10 nanostructures with different shapes (such as nanoparticles and nanotubes) is investigated. These nanostructures are produced by hydrogen processing and focused ion beam milling. The structures exhibit interesting reversal modes and are of present or potential interest for sensors and imaging, as well as magnetic recording.


Interactions And Switching Behavior Of Anisotropic Magnetic Dots, Kory D. Sorge, Arti Kashyap, Ralph Skomski, Lanping Yue, L. Gao, Roger D. Kirby, Sy_Hwang Liou, David J. Sellmyer Jun 2004

Interactions And Switching Behavior Of Anisotropic Magnetic Dots, Kory D. Sorge, Arti Kashyap, Ralph Skomski, Lanping Yue, L. Gao, Roger D. Kirby, Sy_Hwang Liou, David J. Sellmyer

Roger Kirby Publications

The magnetic properties of collections of three soft magnetic nanodots with various aspect ratios are investigated. Permalloy films are first produced by dc magnetron sputtering. Focused ion beam milling is then used to mill dots, each with different shape anisotropy. We find that each of the three dots in the system has a unique switching field, and that there is significant magnetostatic coupling. Micromagnetic simulations suggest that for dot separations of less than 50 nm there exists strong interdot interaction, leading to the possibility of controlled switching of neighboring dots. This switching behavior is of interest in magnetic information processing.


Equivalence Of Sweep-Rate And Magnetic-Viscosity Dynamics, Ralph Skomski, Roger D. Kirby, David J. Sellmyer May 2003

Equivalence Of Sweep-Rate And Magnetic-Viscosity Dynamics, Ralph Skomski, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

The irreversible response of magnetic materials to magnetic fields of arbitrary time dependence is investigated by a master-equation approach. The magnetization reversal is expressed in terms of renormalized magnetization modes, and the resulting set of two-level master equations is solved by direct integration. The theory applies not only to linear energy-barrier laws but also to the physically more reasonable case where the activation energy is a nonlinear function of the applied field. Particular emphasis is on the relation between sweep-rate and magnetic-viscosity dynamics. Other regimes, such as oscillating magnetic fields, can be mapped onto sweep-rate dynamics. Magnetic-viscosity and sweep-rate experiments ...


Activation Volumes In Thin Film And Particulate Systems, Roger D. Kirby, Mingjun Yu, David J. Sellmyer May 2000

Activation Volumes In Thin Film And Particulate Systems, Roger D. Kirby, Mingjun Yu, David J. Sellmyer

Roger Kirby Publications

We consider magnetization reversal and decay in thin film and particulate magnetic systems where thermally activated processes are important. We present measurements on the activation volumes associated with magnetization reversal in CoCrPt thin films. We find that the measured activation volume V* goes through a minimum as the film thickness is decreased from 17.5 to 5.5 nm. We have modeled this behavior qualitatively by assuming that the energy barrier to thermally activated reversal varies as 1/H, as has been predicted for incoherent nucleation processes and thermally activated domain–wall motion. This model also predicts that V* varies ...


Enhancement Of Coercivity In Nanometer-Size Copt Crystallites, Sy_Hwang Liou, S. Huang, Elizabeth S. Klimek, Roger D. Kirby Apr 1999

Enhancement Of Coercivity In Nanometer-Size Copt Crystallites, Sy_Hwang Liou, S. Huang, Elizabeth S. Klimek, Roger D. Kirby

Roger Kirby Publications

In this study, we showed that a magnetic coercivity (Hc) as high as 37 kOe was obtained in a CoPt thin film that contains separated nanometer-size CoPt crystallites. We prepared CoPt thin films with thicknesses of 5 and 175 nm by magnetron sputtering. After annealing in an Ar/H2 atmosphere at temperatures from 650 to 750 °C for 3–12 h, we measured the magnetic properties and found that magnetic Hc relates to annealing temperature, annealing time and film thickness. From atomic force microscopy and magnetic force microscopy studies, the magnetic single domain size of CoPt is ...


Activation Entropy, Activation Energy, And Magnetic Viscosity, Ralph Skomski, Roger D. Kirby, David J. Sellmyer Apr 1999

Activation Entropy, Activation Energy, And Magnetic Viscosity, Ralph Skomski, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

Starting from an exact quantum-statistical description, the influence of the shape of the energy landscape on the magnetic viscosity is investigated. Magnetic phase-space analysis based on Kramers’ escape-rate theory of chemical reaction kinetics theory shows that the activation entropy associated with thermally activated hopping modifies the magnetic viscosity by reducing the attempt-frequency prefactor compared to an earlier prediction by Brown [W. F. Brown, Phys. Rev. 130, 1677 (1963)]. Energetic contributions are analyzed in terms of a model applicable to a range of coherent and noncoherent magnetization processes, and in the long-time limit deviations from the linear logarithmic magnetic-viscosity law are ...


Magnetic And Structural Properties Of Prco3–XSiX Compounds, T. Matsui, R. D. Stevenson, Roger D. Kirby, David J. Sellmyer Jun 1998

Magnetic And Structural Properties Of Prco3–XSiX Compounds, T. Matsui, R. D. Stevenson, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

We have systematically investigated the magnetic properties of the rare-earth compounds PrCo8Si and PrCo3–xSix, the crystal structures of which are hexagonal CeNi3-type and rhombohedral Be3Nb-type, respectively. Sharp cusps were observed in the real and imaginary parts of the ac susceptibility at temperatures between 282 (x = .08) and 209 K (x = .23). Also observed were bifurcations of the zero-field-cooled and field-cooled magnetization curves at the same temperatures, showing that the magnetization was irreversible below these temperatures. The effect of Si substitution for Co in this system is to decrease the average ...


Optical And Magneto-Optical Properties Of Mnpt3 Films (Abstract), Kurt W. Wierman, J. N. Hilfiker, Renat F. Sabiryanov, Sitaram Jaswal, Roger D. Kirby, John A. Woollam Apr 1997

Optical And Magneto-Optical Properties Of Mnpt3 Films (Abstract), Kurt W. Wierman, J. N. Hilfiker, Renat F. Sabiryanov, Sitaram Jaswal, Roger D. Kirby, John A. Woollam

Roger Kirby Publications

Optically thick films of MnPt3 were prepared by magnetron sputtering onto quartz substrates. Postdeposition annealing at 850 °C resulted in highly textured (111) films with the L12 (Cu3Au) structure. MnPt3 films are ferromagnetic with a Curie temperature of 380 °C, and they show large magneto-optical effects in the visible. These films also show a high degree of long-range order. The diagonal components of the dielectric tensor were determined using variable angle spectroscopic ellipsometry measurements over the spectral range 1.2–2.4 eV. Magneto-optic Kerr rotation and ellipticity measurements were made at near normal ...


Magnetic Properties And Magnetization Reversal In Co/Au Multilayers (Abstract), Z. S. Shan, J. X. Shen, Roger D. Kirby, David J. Sellmyer Apr 1996

Magnetic Properties And Magnetization Reversal In Co/Au Multilayers (Abstract), Z. S. Shan, J. X. Shen, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

We report studies of magnetic properties in CoX Å/Au60 Å multilayers (X = 5,6,7,8,12,20 Å), which were prepared by sputtering on Si(111) substrates, with emphasis on the magnetization reversal. Magnetization reversal was investigated by measurements of initial magnetization curves, minor loops, coercivity as a function of the maximum field of minor loops, temperature dependence of magnetic properties using Kronmüller’s model, time decay of Kerr rotation angle UK, and the field-sweep speed dependence of coercivity Hc(dHa/dt) at room and/or low temperature. It is found that (1) the thermal ...


Magnetic And Magneto-Optical Properties Of MnXPt1–X–YZnY, Kurt W. Wierman, Roger D. Kirby Apr 1996

Magnetic And Magneto-Optical Properties Of MnXPt1–X–YZnY, Kurt W. Wierman, Roger D. Kirby

Roger Kirby Publications

In this work we have prepared thin films of the ternary alloy MnxPt1–x–yZny by magnetron sputtering onto quartz substrates. We have found a wide range of compositions which are strongly ferromagnetic at room temperature. A transition from a cubic to tetragonal phase with decreasing Pt content is confirmed by x-ray diffraction. X-ray diffraction measurements also show a strong (001) reflection consistent with long range order along the c axis for the tetragonal phase. These films show large complex Kerr rotations (up to 0.7°) in the visible spectrum. This combined with their anisotropic ...


Long-Range Order And Magnetic Properties Of MnXPt1 – X Thin Films, Kurt W. Wierman, Roger D. Kirby Mar 1996

Long-Range Order And Magnetic Properties Of MnXPt1 – X Thin Films, Kurt W. Wierman, Roger D. Kirby

Roger Kirby Publications

Thin films of MnxPt1–x (x = 0.18, 0.22, 0.25, 0.30, 0.34) were prepared by magnetron sputtering onto quartz substrates. After annealing in vacuum for 1 h at 850°C, X-ray diffraction indicates that the films have the Cu3Au cubic structure (a = 3.87 Å) and are highly textured with the (111) axis along the film normal. These samples have a high degree of long-range order, as indicated by the ratio of the intensities of the superlattice (100) and fundamental (200) X-ray diffraction reflections. We report here the results of magnetic ...


Magneto-Optical And Structural Properties Of Bialdylg/Fe Multilayers, J. X. Shen, Kurt W. Wierman, Y. B. Zhang, Roger D. Kirby, John A. Woollam, David J. Sellmyer May 1994

Magneto-Optical And Structural Properties Of Bialdylg/Fe Multilayers, J. X. Shen, Kurt W. Wierman, Y. B. Zhang, Roger D. Kirby, John A. Woollam, David J. Sellmyer

Roger Kirby Publications

Bi- and Al-doped DyIG(y Å)/Fe(x Å) (y = 50 to 130 Å and x = 5 to 15 Å ) multilayer thin films were made by magnetron sputtering onto Si(111) substrates. Rapid thermal annealing was used to crystallize these garnet multilayers. The crystallized multilayer samples possess well-defined interfaces. Atomic force microscopy showed that the annealed samples had smooth surfaces, with small grain sizes (~30 to 80 nm). All of the samples had perpendicular magnetic anisotropy with very square hysteresis loops. The coercivity was found to vary from 600 Oe to 2 kOe, depending on Fe thickness and annealing conditions ...


Magnetic And Magneto-Optic Properties Of Sputtered Co/Ni Multilayers, Y. B. Zhang, P. He, John A. Woollam, J. X. Shen, Roger D. Kirby, David J. Sellmyer May 1994

Magnetic And Magneto-Optic Properties Of Sputtered Co/Ni Multilayers, Y. B. Zhang, P. He, John A. Woollam, J. X. Shen, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

We have investigated the magnetic and magneto-optic properties of Co/Ni multilayers deposited on Ag and Au buffer layers. The samples with Au buffer layers show perpendicular magnetic anisotropy, but those with Ag buffer layers do not. The. structure and degree of crystalline alignment of the buffer layer are evidently crucial to development of perpendicular magnetic anisotropy. We also present the results of polar Kerr rotation measurements as a function of wavelength and layer thickness of the multilayers.


Temperature-Dependent Interface Magnetism And Magnetization Reversal In Co/Pt Multilayers, Z. S. Shan, J. X. Shen, Roger D. Kirby, David J. Sellmyer, Y. J. Wang May 1994

Temperature-Dependent Interface Magnetism And Magnetization Reversal In Co/Pt Multilayers, Z. S. Shan, J. X. Shen, Roger D. Kirby, David J. Sellmyer, Y. J. Wang

Roger Kirby Publications

We report on the temperature dependence of the magnetic properties and interface magnetism of Co/Pt multilayers. The magnetic properties including magnetization and anisotropy change substantially as the temperature varies from 300 to 10 K for samples with Co layer thickness in the range from 3 to 7 Å. The interface anisotropy of about 0.38 erg/cm2 is nearly independent of temperature. The magnetization reversal is dominated by domain wall motion for the thinner Co layers and dominated by nucleation for the thicker Co layers.


Low-Temperature Characterization Of The Magnetic Properties Of Mnbial Thin Films, Kurt W. Wierman, J. X. Shen, Roger D. Kirby, David J. Sellmyer May 1994

Low-Temperature Characterization Of The Magnetic Properties Of Mnbial Thin Films, Kurt W. Wierman, J. X. Shen, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

The magnetic properties of thin-film samples of MnBi0.8Alx with aluminum concentrations of x = 0.0, 0.4, 0.6, and 0.8 were systematically studied over a temperature range of 20 to 300 K. The as-deposited films are amorphous and nonmagnetic, but highly textured polycrystalline films that are ferromagnetic are formed by annealing at 350 °C. Our measurements show that the coercivity of such films rapidly decreases, then approaches a constant value (4 kOe for x = 0.4) with increasing annealing time. Magnetic measurements show that both anisotropy and coercivity decrease with decreasing temperature. Unlike bulk ...


Magnetization Reversal In Compositionally Modulated Tb/Fe Multilayers (Abstract), Roger D. Kirby, J. X. Shen, David J. Sellmyer May 1994

Magnetization Reversal In Compositionally Modulated Tb/Fe Multilayers (Abstract), Roger D. Kirby, J. X. Shen, David J. Sellmyer

Roger Kirby Publications

We have prepared compositionally modulated Tb(X Å) thin film multilayers with X ranging from 3.5 to 7 Å by magnetron sputtering on glass substrates. Magnetization measurements using SQUID and alternating gradient force magnetometers show that these samples have uniaxial anisotropies (Ku) up to 107 erg/cm3 and saturation magnetizations (Ms) between 50 and 350 emu/cm3. Constant field magnetization reversal measurements at room temperature show that these samples reverse by slow nucleation followed by relatively rapid domain wall motion. The samples with larger uniaxial anisotropies and smaller saturation magnetizations reverse completely for applied ...


Electronic Structure And Magneto-Optical Properties Of Mnbi And Mnbial, Sitaram Jaswal, J. X. Shen, Roger D. Kirby, David J. Sellmyer Apr 1994

Electronic Structure And Magneto-Optical Properties Of Mnbi And Mnbial, Sitaram Jaswal, J. X. Shen, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

MnBiAl films are of considerable current interest for possible magneto-optical applications because of their perpendicular anisotropy, large polar Kerr rotation, reduced grain size, and structural stability. We report here experimental and theoretical studies of the effect of Al alloying on the electronic structure and magneto-optical properties of MnBi. Our measured spectral dependencies of the polar Kerr rotation in the two systems are similar. We carried out relativistic self-consistent spin-polarized electronic structure calculations on MnBi and MnBiAl, and the calculated densities of states are in good agreement with available x-ray photoemission spectroscopy data for both materials. The spin magnetic moment of ...


Magnetization Reversal And Defects In Co/Pt Multilayers, J.X. Shen, Roger D. Kirby, K. Wierman, Z.-S. Shan, David J. Sellmyer, T. Suzuki May 1993

Magnetization Reversal And Defects In Co/Pt Multilayers, J.X. Shen, Roger D. Kirby, K. Wierman, Z.-S. Shan, David J. Sellmyer, T. Suzuki

Roger Kirby Publications

(Co 3 Å/Pt 10 Å)× N (N=8, 16, and 30 bilayers) multilayer thin films were prepared by sputtering onto an 850-Å-thick SiN layer that had been deposited on a silicon (111) substrate. We used the polar Kerr effect to measure the time dependence of magnetization reversal over the temperature range 90–300 K. Direct domain observations were also carried out. The results show that the domain expansion process depends strongly on the number of bilayers. Uniform domain expansion was found only in the thinner samples. From the time dependence of the magnetization reversal measurements over the temperature range ...


Magnetization Reversal In Co/Cr Multilayer Films, D. Wang, Roger D. Kirby, B. W. Robertson, David J. Sellmyer May 1993

Magnetization Reversal In Co/Cr Multilayer Films, D. Wang, Roger D. Kirby, B. W. Robertson, David J. Sellmyer

Roger Kirby Publications

Magnetization reversal of Co/Cr multilayer films is studied by utilizing initial magnetization curves, minor loops, isothermal and dc demagnetization remanence curves, and temperature dependence of the loops. Electron microscope observations reveal that the films consist of columnar grains of size from 400 to 800 Å. It is suggested that the magnetization reversal is dominated by rotation of single-domain grains. Numerical calculations are performed based on the Stoner–Wohlfarth coherent rotation model for noninteracting, single-domain particles of uniaxial anisotropy. The calculated results agree qualitatively with the experimental results. To investigate the quantitative differences, magnetic interactions among the grains are measured ...


Studies Of Domain Dynamics In Amorphous Dy/Fe Multilayers, Roger D. Kirby, J.X. Shen, Z.S. Shan, David J. Sellmyer Nov 1991

Studies Of Domain Dynamics In Amorphous Dy/Fe Multilayers, Roger D. Kirby, J.X. Shen, Z.S. Shan, David J. Sellmyer

Roger Kirby Publications

Compositionally-modulated Dy/Fe films were prepared by dc magnetron sputtering onto glass substrates. For this series of samples, the Dy thickness was fixed at 5 Å, while the Fe thickness was varied from 4 to 6 Å. To study the magnetization reversal, the samples were first saturated. The magnetic field was then reversed to a value near the coercive field, and the Kerr rotation was measured as a function of time after reversal. We interpret our results in terms of the model of domain reversal first described by Fatuzzo for ferroelectrics. For some Fe thicknesses, we found that the reversal ...


Magneto-Optical Properties Of Mnbial Thin Films, J. X. Shen, Roger D. Kirby, David J. Sellmyer, Y. J. Wang Apr 1991

Magneto-Optical Properties Of Mnbial Thin Films, J. X. Shen, Roger D. Kirby, David J. Sellmyer, Y. J. Wang

Roger Kirby Publications

Mn-Bi-Al thin films. were produced by sequential evaporation of the constituents, followed by an anneal at 300 °C. The temperature and composition dependencies of the Kerr rotation angle, absolute reflectivity, and magnetic anisotropy were measured. The results show that, up to 30 at. % Al concentration, the thin films retain the pure MnBi hexagonal structure. Further, for suitable Al content, the films have the same large Kerr rotation as MnBi. Pure MnBi films exhibit perpendicular anisotropy at room temperature and in-plane anisotropy for temperatures below 142 K. In contrast,. the Al-doped films prepared here have perpendicular anisotropy down to at least ...


Magneto-Optic Properties Of Uranium-Based Compounds, Roger D. Kirby, J. X. Shen, John A. Woollam, David J. Sellmyer Apr 1991

Magneto-Optic Properties Of Uranium-Based Compounds, Roger D. Kirby, J. X. Shen, John A. Woollam, David J. Sellmyer

Roger Kirby Publications

Uranium-based compounds often show interesting magnetic properties and large polar Kerr rotations. Because of this, the wavelength and temperature dependencies of the polar Kerr rotation in several uranium-based compounds, including UMn2Ge2, UFe2, and UGa2, have been investigated. The Mn moments order ferromagnetically in UMn2Ge2 below 380 K, and while the U moments do not order ferromagnetically until the temperature is below 150 K. The measurements presented here show that the size of the Kerr rotation increases from 0.05° at room temperature to 0.15° when the U moments are ordered. The ...


The Structure And Magneto-Optic Properties Of Mnal-Based Thin Films, J.X. Shen, Roger D. Kirby, David J. Sellmyer May 1990

The Structure And Magneto-Optic Properties Of Mnal-Based Thin Films, J.X. Shen, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

We have measured the magnetization and magneto-optic Kerr rotation of sputtered thin films of Mn-Al-Cu ternary alloys over a wide composition range and for substrate temperatures between 25 and 450 °C. Magnetization and x-ray diffraction measurements suggest that our films are a mixture of the ferromagnetic kappa (κ) phase of MnAl and a highly paramagnetic amorphous phase. Room-temperature magneto-optic measurements on these films show a saturation polar Kerr rotation of up to 0.12° with little wavelength dependence.


The Electrical Noise Of Carbon Fibers, R.O. Dillon Nov 1989

The Electrical Noise Of Carbon Fibers, R.O. Dillon

Roger Kirby Publications

The low-frequency excess electrical noise has been measured on carbon fibers with a wide range of crystalline perfection and corresponding electrical and mechanical properties. Fibers include those prepared from ex-PAN and ex-pitch polymers, and a catalytic-chemical vapor deposited filament. The extensional (Young's) moduli of these fibers varied from about 220 to 890 GPa (35–130 Msi), while the electrical resistivities varied from about 19 to 1 µΩ m. The low-frequency electrical noise of each fiber was found to be proportional to l2 and to vary as 1/fα, where f is the frequency and α is about ...


Metastable Conduction States In Mo2S3: Pulse Conductivity And Thermoelectric Power, Roger D. Kirby, R.L. Fagerquist Aug 1988

Metastable Conduction States In Mo2S3: Pulse Conductivity And Thermoelectric Power, Roger D. Kirby, R.L. Fagerquist

Roger Kirby Publications

Mo2S3 is a linear-chain-structure compound which has two inequivalent zig-zag Mo chains parallel to the b axis. It undergoes at least two phase transitions below room temperature (at 182 and 145 K upon cooling). X-ray-diffraction measurements show that both incommensurate and commensurate structural distortions are associated with the phase transitions. We repot here the results of electrical-conductivity and thermoelectric-power measurements on Mo2S3 . By using pulsed electric currents to rapidly heat and cool the sample while electrical-resistivity or thermoelectric-power measurement are being made, we are able to show that below the lower-temperature phase transition, the ...


Lattice Dynamics Of Mixed Crystals Of Tise2, Roger D. Kirby, G.A. Freund, Jr. Dec 1984

Lattice Dynamics Of Mixed Crystals Of Tise2, Roger D. Kirby, G.A. Freund, Jr.

Roger Kirby Publications

We present the results of Raman scattering measurements on the mixed-crystal systems TiSe2-xSx, TiSe2-xTex, ZrxTi1-x Se2. At room temperature with the pure compounds all have crystal structures represented by the D3d(P3̃m1) space group with three atoms per unit cell. There are two Raman-active k=0 phonons, one of A1gˉ symmetry and one of Eg symmetry. In the TiSe2-xTex system, the A1gˉ and E phonon frequencies shift smoothly with concentration, and the shifts are well described by a simple virtual-crystal model ...


Effect Of Nickel Impurities On Charge-Density-Wave Formation In Tas3, M.H. Rashid, David J. Sellmyer, Roger D. Kirby May 1984

Effect Of Nickel Impurities On Charge-Density-Wave Formation In Tas3, M.H. Rashid, David J. Sellmyer, Roger D. Kirby

Roger Kirby Publications

Introduction of nickel impurities into TaS3 has the effect of smearing the charge-density-wave transitions in TaS3 of both orthorhombic and monoclinic phases. The orthorhombic doped crystals show non-Ohmic conductivity beyond threshold fields that are much larger than the threshold field of the pure phase, possibly due to additional pinning of the charge-density wave by nickel impurities. The charge-density-wave state is completely destroyed as 10 at % or more Ta atoms are replaced by Ni atoms and metallic behavior between 4.2 and 30 K is observed in these cases.