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The metal–insulator transition and underlying spin dynamics in La0.7D0.3MnO3 (D=Ca, Sr) are investigated using optical pump–probe spectroscopy at 1.5 eV. Our measurements, which span the ferromagnetic–paramagnetic transition temperature, reveal that the dynamics of the optically induced spectral weight transfer follow the temperature dependence of the magnetic specific heat. This dependence reflects the intrinsic interdependence between the optical conductivity and magnetism in the manganites allowing for the determination of the spin-lattice coupling magnitude.

We report a systematic study of the microstructure and dielectric properties of barium strontium titanate, Ba1−xSrxTiO3, films grown by laser ablation on LaAlO3 substrates, where x=0.1–0.9 at an interval of 0.1. X-ray diffraction analysis shows that when x 0.4, compared with the peak temperatures of the bulk Ba1−xSrxTiO3. At room temperature, the dielectric constant and tunability are relatively high when x⩽0.4 but start to decrease rapidly as x increases.

We have used a coplanar waveguide structure to study broadband electrodynamic properties of single-crystal and thin-film strontium titanate. We have incorporated both time- and frequency-domain measurements to determine small-signal effective refractive index and loss tangent as functions of frequency (up to 4 GHz), dc bias (up to 106 V/m), and cryogenic temperature (17 and 60 K). The large-signal impulse response of the devices and the associated phenomenological nonlinear wave equation illustrate how dissipation and nonlinearity combine to produce the overall response in the large-signal regime.

We have studied electromagnetic pulse shaping in coplanar waveguide delay lines made from superconducting YBa2Cu3O7−δ electrodes on nonlinear dielectric SrTiO3 single-crystal substrates. The delay lines exhibited bias- and temperature-dependent nonlinearity and dispersion, with associated pulse-shaping effects. At low temperatures and under certain bias conditions, the interplay of dispersion and nonlinearity has led to stable and compact wave forms, reminiscent of microwave solitons.

We have systematically studied the temperature- and magnetic field-dependent resistance in (La0.5Sr0.5)CoO3 (LSCO) films with various degrees of in-plane texturing using the biaxially oriented LSCO on CeO2/YSZ/SiO2/Si substrates. We find that the ferromagnetic transition temperature, Tc, is much the same in all samples while the resistive transition exhibits metallic behavior (dR/dT>0) in the epitaxial LSCO to semiconducting behavior (dR/dT

We report on the fabrication of ferromagnet–insulator–ferromagnet junction devices using a ramp-edge geometry based on (La0.7Sr0.3)MnO3 ferromagnetic electrodes and a SrTiO3 insulator. The maximum junction magnetoresistance (JMR) as large as 23% is observed below 300 Oe at low temperatures (T

We are optimizing thin films of perovskite manganese oxides for bolometric applications. We have studied the relevant material characteristics of several members of this family namely, La0.7Ba0.3MnO3, La0.7Sr0.3MnO3, La0.7Ca0.3MnO3, and Nd0.7Sr0.3MnO3. Here, we discuss issues related to the choice of material, the influence of deposition parameters, and postdeposition heat treatments on the relevant characteristics such as the resistivity-peak temperature (Tp) and the temperature coefficient of resistance (TCR). For a given material, a higher peak temperature implies a larger temperature coefficient of resistance. In contrast, on comparing different material systems, the TCR tends to decrease as Tp increases.

We report our study of the effect of crystallinity on the magnetoresistance in epitaxial and polycrystalline La2/3Ba1/3MnO3 and La2/3Ca1/3MnO3 thin films. Magnetoresistance in epitaxial films exhibits field dependence and temperature dependence similar to bulk single crystals and sintered bulk ceramics. The polycrystalline films exhibit a markedly different behavior. The magnetoresistance in this case shows either a monotonic increase or saturation with decreasing temperature in contrast to that of epitaxial films in which the magnetoresistance peaks close to the ferromagnetic transition temperature. The field dependence in the polycrystalline films is also remarkably different. At low fields, we observe a sharp drop in resistance followed by a more gradual decrease at higher fields. Our data suggest that in addition to the intrinsic magnetoresistance, grain-boundary transport contributes significantly to the magnetoresistance in polycrystalline films.

Thin films of colossal magnetoresistance (MR) material, La0.67Ca0.33MnO3, were implanted with different doses (1011–1015 ions/cm2) of 200 keV Ar+ ions. The implanted samples were examined by ion channeling and x‐ray diffraction techniques. The channeling results clearly showed that the magnitude of the induced lattice disorder did not increase greatly for implantation doses up to 5×1013 ions/cm2. In this low dose implantation regime, the magnetoresistance {MR=[R(0)−R(H)]/R(0)} increased by 50%, the peak resistivity went up by two orders of magnitude, and the magnetoresistivity peak temperature decreased by 130 K compared to the original, unimplanted sample. For doses ≥5×1013 ions/cm2, the damage was significant and caused the sample to become semiconducting.

We are able to grow high quality La0.67Sr0.33MnO3(LSMO) colossal magnetoresistive (CMR) thin films on Y‐stabilized zirconia (YSZ) buffered (100) Si substrates using a Bi4Ti3O12 texturing and lattice matching layer. The CMR films have very high structural perfection and show excellent transport and ferromagnetic properties, including the almost full saturation magnetization values and narrow ferromagnetic resonance peaks (15 Oe at 290 K). The lattice matching template/buffer layer approach is suitable for the high quality CMR films on Si. A close correlation between the magnetic hysteresis loop and the field dependence of MR is observed at lower temperatures.

We report measurements of 1/f electrical noise in two hole doped manganite perovskite oxides, La0.67Ca0.33MnO3 and Pr0.67Sr0.33MnO3, which exhibit colossal magnetoresistance. The noise magnitude represented by the Hooge parameter is nearly 8 orders of magnitude larger than that observed in ordinary metals (and semiconductors) and nearly 5–6 orders of magnitude larger than that observed in epitaxial films of the perovskite oxide YBa2Cu3O7 in the normal state. The normalized noise spectral density increases with decreasing temperature below the resistivity peak, suggestive of the presence of additional low energy noise processes in the ferromagnetic metallic state.

We report measurements of the low‐frequency optical response in epitaxial thin films of La0.67Ca0.33MnO3 in the temperature range covering both the ferromagnetic metallic state and the paramagnetic insulating state. We observe a bolometric optical response in fully oxygenated films of the above composition as well as in oxygen deficient films. In both types of samples, the optical response is thermal in nature as indicated by its proportionality with the temperature derivative of the resistance dR/dT.

We report the magnetic field dependence of microwave absorption at low fields (200 Oe), in thin film and bulk samples of La1−xBaxMnO3−z. We demonstrate, using a very simple cavity configuration, that the magnetic field sensitivity of the microwave response of the giant magnetoresistance materials offers possibilities of using such materials in devices operating at low fields. Low‐field dc magnetization and ac resistivity measurements are also presented.

We report the observation of giant magnetoresistance near room temperature in ferromagnetic films of La1−xSrxMnOz for 0.16≤x≤0.33. For B=5 T, the maximum magnetoresistance ratio [R(0)−R(B)]/R(0) of an annealed film is 60% at 260 K for x=0.2, and 35% at 330 K for x=0.33. Annealed films have higher Curie temperature (Tc), a larger saturation moment and a larger magnetoresistance effect near Tc than do as‐grown films. The temperature dependence of resistivity for all the samples investigated is unusual, activated above Tc and metallic below Tc. This and the giant magnetoresistance are possibly explained by scattering from magnetic polarons which dominate the transport near Tc.

We have investigated the optical response from a single grain boundary in a thin film (∼300 nm) of superconducting YBa2Cu3O7−δ fabricated on bicrystals SrTiO3 substrate. We have studied the temperature, bias current, and magnetic field dependence of the optical response in the temperature range of 15 K≤T≤35 K. We find that the optical response from the single grain boundary in this temperature range can be satisfactorily explained in terms of the optical response of a Josephson weak link. The optical response of the grain boundary is qualitatively similar to that of granular films seen in the earlier studies, indicating that the latter may be dominated by the optical response of grain‐boundary weak links.

We have investigated the optical response of epitaxial ultrathin (3 nm) YBa2Cu3O(7-delta) film on an NdGaO3 substrate and thin (50 nm) film of YBa2Cu3O(7-delta) on a bicrystal SrTiO3 substrate. While the current-voltage characteristics of the ultrathin film indicate a Kosterlitz-Thouless transition (associated with vortex-antivortex unbinding) at a temperature T(KT), we do not observe any optical response at or below T(KT). An enhanced optical response with nonbolometric characteristics was observed from the grain-boundary as compared to the bolometric optical response of the epitaxial film at the resistive transition. These results indicate that the grain-boundary weak links play a significant role in the enhanced optical response near Tc.

Bilayers of Y1Ba2Cu3O7−x(YBCO)/Nd1.85Ce0.15CuO4−y(NCCO), in which both layers were superconducting, were fabricated in situ by pulsed laser deposition. Using N2O as the reactive gas, we were able to meet the conflicting processing requirements, oxygenation for YBCO, and reduction for NCCO, in the same sample with a specific cooling procedure. The bilayer thin films were c‐axis oriented with a transition temperature, Tco, of 88.5 K for YBCO and 18.5 K for NCCO. Supercurrent was observed across the interface of the YBCO and NCCO superconducting layers, indicating the phase coherence between these superconductors.

YBa2Cu3O7−δ (YBCO) films with nominal thicknesses of 1–4 unit cells were grown by pulsed laser deposition using (PrxY1−x)Ba2Cu3O7−δ [(PrxY1−x)BCO] (1≥x≥0) as buffer layers and cap layers. The films of 1 unit cell thick were superconducting for all the x values while Tc increased when x was reduced. For adjacent layers of (Pr0.6Y0.4)BCO which is semiconducting, a Tc of 43 K and Jc of 2×106 A/cm2 for B∥ab and 4×105 A/cm2 for B⊥ab at B=7 T and 4.2 K were obtained in a one‐unit cell thick YBCO layer. The Jc values of a few unit cell thick YBCO layers nearly approached that of thick YBCO films. The results suggest the absence of significant weak‐link effects in these films.

A multilayer high Tc superconducting field‐effect transistor‐like structure was made from ultrathin YBa2Cu3O7−x films. An epitaxially grown dielectric SrTiO3 insulation layer, which had a forward bias breakdown voltage of about 20 V, allowed an electric field induced change in the channel layer of 1.25×1013 carrier/cm2 per volt of the gate voltage. A significant modulation of the normal state and superconducting properties was observed in samples with YBa2Cu3O7−x channel layers of a few unit cells thick. By applying gate voltage of different polarities, Tc was both suppressed and enhanced by ∼1 K. The resistance was modulated by as much as 20% in the normal state and by over 1500% near the zero resistance temperature.