This work presents research on the one-microsecond, L-band relativistic klystron amplifier (RKA) project conducted at Los Alamos National Laboratory. A collection of theoretical analyses is presented for rf cavities, intense electron beams, beam-cavity interactions, and small-signal klystron bunching. Electromagnetic field simulations were done for three dimensional cavity structures using HFSS with very accurate results. Particle-in-cell simulations of the complete RKA were done using the two dimensional code ISIS. Extraction efficiency for intense modulated beams is discussed and verified in simulations. Designs for input and idler cavities are reviewed. Extremely low-Q, single-gap, output cavities are investigated for coupling rf power from very low-impedance, modulated, electron beams. Output cavities with a Q less than 4 have been designed, measured, and tested. Methods were implemented for designing 2D equivalent output cavity structures to model 3D structures in 2D codes. A technique for ex-situ rf conditioning of the output cavity gap pieces is presented. A beam-pipe center conductor, intended to reduce the space-charge potential depression of the beam, is discussed. Diagnostics for intense-beam and high-power rf measurements are presented. A coaxial directional coupler and load, capable of handling more than 500 MW at 1300 MHz, were designed. Mode conversion from coax to waveguide is discussed for $>$100 MW power levels. Methods for determining the gap voltage in an operating cavity are presented. Pulse-shortening of the rf in the RKA is also discussed. A 650 kV, 5 kA, one-microsecond, annular beam has been produced from a stainless-steel, explosive-field-emission cathode. The beam current was modulated up to 70% $(I\sb1 /I\sb0$ = 70%) using a two-cavity bunching section operating at 1300 MHz. RKA structures simulated in ISIS have extracted up to 250 MW. This number was consistent with the extracted power actually measured in the equivalent experiment. Overall energy extraction was as high as 160 J per pulse. The average rf output power coupled into the 6-inch-diameter coax transmission line was approximately: 300 MW for 300 ns, 250 MW for 500 ns, and 100 MW for 1 $\mu$s. Peak power levels as high as 475 MW have also been produced.

A number of different methods for electrically characterizing ZnSe thin films are presented. These include the Hall effect, current-voltage profiling, and capacitance-voltage profiling. The planar Schottky technique is used to analyze p-type ZnSe. The conductance method of Nicollian and Brews is applied for the first time to the ZnSe/GaAs MIS system to find the surface state density profile and the time constants associated with particular states. A novel photowash technique is used to make the GaAs surface gallium rich before ZnSe growth. Electron Paramagnetic Resonance is discussed in the context of probing thin film semiconductors. Room temperature mobilities for undoped, 1 $\rm\mu m,$ ZnSe films grown by Laser-assisted Metal Organic Chemical Vapor Deposition are as high as 309 $\rm cm\sp2/V$-s. Measured mobilities at 77 K are low due to hole conduction in p-type GaAs at the interface. Heterojunction barrier heights are found to be in the range of 0.6-0.9 eV and are most likely due to interface traps. Schottky diode n-values are found to be high ($>$30) because of the heterojunction barrier. P-type conduction in the nitrogen-doped samples has not been found. Undoped ZnSe is n-type and is typically depleted of carriers. Surface state densities for both untreated and Ga-rich ZnSe/p-GaAs interfaces are found to be in the range of $10\sp{12}$ $\rm cm\sp{-2}$-$\rm eV\sp{-1}.$

Impurities have a wide range of effects in interacting quantum many-body systems. They can interplay with interactions and lead to new electronic states of matter. They can also serve as a probe of an "intrinsic" many-body system. In this thesis, we consider the effects of impurities in three quantum many-body systems. First, we study the transport properties of a two-dimensional interacting electronic system with dilute quenched disorder. We find that the ground state is in fact a metallic state and in-plane magnetic-field can drive it to an insulating one. Second, we address the orthogonality catastrophe in Bose-Einstein condensate with a local impurity at its center. It is shown that the orthogonality effect in a Bose system has a stretched-exponential form, stronger than the algebraic orthogonality of a Fermi counterpart. The corresponding absorption spectrum is also determined. Finally, we analyze the effects of a spin resonance mode on the scattering tunneling microscopy(STM) spectra of a d-wave superconductor near a potential scattering center. We identify a counterintuitive two-unit-cell spatial modulation, at o ≃ +/-(Delta0 + O0)/h, where Delta 0 is the energy gap and O0 is the resonance mode energy. This effect can be tested by the Fourier-transformed STM technique.

A series of improvements to the Rice Field Model (RFM) are described, which both increase the accuracy and extend the capabilities of the model. A new ring current parameterization improves the determination of storm-time fields in the inner magnetosphere. Replacement of the tail current module with a more flexible representation also contributes to improved accuracy in the inner magnetosphere, and enables realistic variations in current strength and orientation over the entire magnetotail length. Revision of the tail shielding/interconnection field eliminates inconsistencies in the model magnetotail, and permits variation in the normal component distribution over the tail portion of the magnetopause. The enhanced flexibilities of the interconnection field and cross-tail current module make possible the modeling of variations in the interplanetary magnetic field (IMF) as it propagates downstream, thereby advancing the steady-state RFM an important step toward time-dependent modeling. The modified RFM is used to explore a number of time-dependent magnetospheric phenomena. In simulations of the March 1998 magnetic storm, the new model displays an improved representation of the inner magnetosphere, accurately predicting both storm-induced variations and day-night asymmetry in the field at geosynchronous orbit. The effects of time-dependent interplanetary fields on magnetospheric convection are examined, using a new method to compute ionospheric flow and electric fields in non-steady configurations. This method is applied to simulations of the growth and contraction of the polar cap in Southward and Northward turnings of the IMF. Model convection patterns for Southward turnings are shown to be consistent with theoretical expectations. The RFM is also used to simulate polar cap convection in the particular IMF conditions believed to trigger formation of the theta aurora. The results of the simulation prove to be consistent with several observed properties of the theta aurora, and shed light on the plasma sheet and magnetotail configurations associated with this phenomenon.

Near field recording on high coercivity FePt intermetallic compound media using a high Bsat write element was investigated. Untextured FePt media were prepared by magnetron sputtering on ZrO2 disks at a substrate temperature of 450°C, with post annealing at 450°C for 8 hrs. Both multilayer and cosputtered precursors produced the ordered tetragonal L10 phase with high coercivity between 5kOe and 12kOe. To improve readback noise decrease magnetic domain size, FePtB media were subsequently prepared by cosputtering. Over-write, roll-off, signal to noise ratio and non-linear transition shift (NLTS) ere measured by both metal in gap (MIG) and merged MR heads. FePtB media showed similar NLTS to commercial CoCrPtTa longitudinal media, but 5dB lower signal to noise ratio. By operating recording transducers in near contact, reasonable values of (>30dB) could be obtained. VSM Rotational Transverse Magnetization has been used for measuring the anisotropy field of magnetic thin films. Magnetization reversal during rotation of a 2D isotropic an applied field is discussed. The relationship between the transverse magnetization My and the applied field H was numerically solved. An excellent approximation for the transverse magnetization is found to be: My/Ms=A1-H/Hk 2.5, where A = 1.1434, and Hk is the anisotropy field. For curve fitting to experimental data, both A and Hk were used as fitting parameters. Comparison between a constructed torque hysteresis method and this VSM RTM method have been made theoretically and experimentally. Both results showed that VSM RTM will give better extrapolation of the anisotropy field. The torque measurement will slightly overestimate the anisotropy field. The anisotropy fields of FePt and FePtX (X = B, Ni) films were characterized using this VSM RTM technique with comparison to a CoCrTaPt disk. Anisotropy energy was derived. Hc/Hk was used as an indicator for coherent rotation of a single domain. Interactions between magnetic domains were characterized by Kelly-Henkel plot and interactive field factor (IFF). Correlation between coercive force and magnetic anisotropy of grains and the degree of magnetic isolation among grains were discussed. B and Ni were used as diluting agents to the FePt system to decrease saturation magnetization, coercivity, anisotropy field and anisotropy energy. They also decrease the magnetic coupling between neighboring domains, and promote coherent rotation inside each domain.

A novel type of nanocrystalline magnetic thin films consisting of ferromagnetic metals and C60 have been developed and investigated. CO-C 60, Fe-C60 and CoFe-C60 with different concentrations of C60 thin films have been manufactured by thermal vapor codeposition. The microstructures and magnetic properties of the films can be significantly enhanced by varying the concentrations of C60 in the films. The stability of C60 and the compatibility of C60 with the metallic matrices are confirmed by mass spectrometry, Raman, WDS, XRD and TEM. Strong metal-C60 interaction is indicated by higher desorption temperatures of C60 in the meta-C60 films than that in pure C60 and the peak shift in Raman spectra. TEM shows that the grain size of the matrix metal decreases proportionally with increasing C60 concentration. Nanosize uniform columnar grains with nanoscale dispersion of C60 on the grain boundaries are commonly observed in the metal-C60 films. A self-assembly grain growth model based on the size effect of C60 and the metal-C60 interaction is proposed to delineate the microstructural evolution by C60. Calculations based on this model are consistent with experimental observations and give a grain size vs. C60 (carbon) concentration relationship. Grain growth retardation by C60 is observed in a CO-C60 film. Out-plane magnetic remanence and coercivity are enhanced in both the CO-C60 and Fe-C60 films. In the in-plane direction, the coercivity deceases in CO-C60 films but increases slightly in Fe-C60 films with increasing C60 concentrations. In-plane magnetic anisotropy is detected in CO-C60 films but not in Fe-C60 films. Strong temperature-dependent magnetization remanence and saturation are found in both the Co-C60 and Fe-C60 films with high C60 concentrations due to the nanosize grain effects. Temperature effects on the coercivity of CO-C60 and Fe-C60 are different and determined by the intrinsic magnetocrystalline anisotropy energy. Coercivity of the CoFe-C60 films increases after annealing above 450°C. An unusual magnetization behavior of the virgin curve intersecting with the major hysteresis loop and fast magnetic switch is observed in a Fe 83C60 film. The magnetic properties are interpreted by MOIF technique and correlated to the film microstructure.

Perpendicular recording has the potential to achieve high-density data storage. As the linear density approaches to the superparamagnetic limit, traditional longitudinal recording may give way to perpendicular recording. This study investigated the possibility of using perpendicular multilayers as an alternative magnetic storage medium. Various cobalt based perpendicular multilayers were deposited. The macro-magnetic properties of the thin films were characterized using switching ratio and $\rm\delta M$ curves. The experimental measurements were correlated with the read/write recording tests. Medium noise analysis on perpendicular multilayers was performed in both time-domain and frequency-domain. The time-domain eigenvector expansion technique was adopted and extended for use in perpendicular recording. In addition, recording non-linearities from perpendicular multilayers have been measured by using pseudo-random binary sequence and the third harmonic ratio measurement. The readback non-linearity of MR head was characterized using a polynomial equation. Both the NLTS and partial erasure measurements show advantages for perpendicular recording compared to longitudinal. Finally, by constructing transformation filters, we demonstrated magnetic recording on perpendicular media via conventional longitudinal channels. A linear recording density of 204 kbpi has been obtained in a peak detection channel while a linear density of 350 kbpi was demonstrated on a partial response maximum likelihood (PRML) channel.

The possibility of the existence of ferromagnetic order in Ru monolayers on the C(0001) graphite surface is studied using electron induced spin-polarized secondary electron emission (SPSEE). Below a surface Curie temperature of approximately 250K we find ferromagnetic order of the Ru monolayer. The growth mode of Ru on C(0001) is investigated by Auger electron spectroscopy (AES). We find, that the initial growth occurs laterally until a homogenous monolayer is formed. Our study provides the first observation of spontaneous, two-dimensional ferromagnetic order of a 4d transition element. To investigate the spin-polarization and domain pattern in ultrathin films and multilayers, we develop a novel technique: scanning ion microscopy with polarization analysis (SIMPA). A highly focused Ga$\sp+$-ion beam from a liquid metal ion source is moved over a sample to locally eject secondary electrons, whose spin-polarization is determined by using a medium energy Mott polarimeter. We show that the sputtering by the ion beam can be well controlled and utilized for nano-lithography and spin-resolved sputter depth profiling. We use SIMPA and the surface magneto-optic Kerr effect to study exchange coupling in Fe/Mn/Fe/Pd(100) multilayers. The intervening Mn layer is grown in a wedge shape ranging in thickness from 0 to 9 monolayers. Our results show that both Fe layers are coupled ferromagnetically for the entire Mn thickness range. Growth mode and structure are analyzed by AES and medium electron energy diffraction.

This thesis describes magneto-optical processes in ferromagnetic (III,Mn)V semiconductors and their heterostructures induced by femtosecond laser pulses. Two-color ultrafast magneto-optical spectroscopy has been developed, which allows us to observe a rich array of dynamical phenomena that are absent in traditional nonmagnetic semiconductors or metallic/insulating magnets. We isolate several distinct temporal regimes in spin dynamics, interpreting the fast (< 1 ps) dynamics as spin heating through sp-d exchange interaction between photo-carriers and Mn ions while the ∼100 ps component as a manifestation of spin-lattice relaxation. Charge carrier and phonon dynamics were also carefully studied, showing an ultrashort charge lifetime of photoinjected electrons (∼ 2 ps) and propagating coherent acoustic phonon wavepackets with strongly probe energy dependent oscillation period, amplitude and damping.

Keepered media refers to traditional magnetic media with the addition of a soft magnetic "keeper" layer adjacent to the recording layer. Numerous recent reports have shown performance improvements associated with keepered media read with inductive heads. This report examines performance changes associated with keepered media read with magneto-resistive heads. This report presents a simple model for MR head response based on imaging, and experimental data in qualitative agreement with this model. Signal and noise spectra for keepered media are also discussed at length, and an optimized keepered media is shown to screen low spatial frequencies, narrowing isolated read pulses. Lastly, substantial noise increases at low spatial frequencies for keepered media are shown, and a possible cause is briefly discussed.