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The impurity (Cr[sup 3+])-doping effect on the stability of charge and orbital ordering has been systematically investigated for Nd[sub 1/2]Ca[sub 1/2]Mn[sub 1-y]Cr[sub y]O[sub 3] crystals by measurements of magnetotransport and x-ray diffraction. The random field in terms of e[sub g] orbital deficiencies on the Cr sites drives the charge and orbital correlations to dynamical and short range, which is most relevant to the high-resistive state exhibiting colossal magnetoresistance. In the Cr-doped manganite, we can observe the coexistence of ferromagnetic-metallic and charge-orbital ordered phases, their spatial distributions, diffuse x-ray scattering, magnetic-field annealing, and the aging effect on the magnetic and electric properties, etc. These phenomena are reminiscent of those of relaxor ferroelectrics composed of ferroelectric clusters embedded in a paraelectric matrix. We propose that the mixed-valent manganite can be viewed as a "magneto- and electrorelaxor." &! copy; 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the phenomena of colossal magnetoresistance or magnetic field induced insulator-metal transitions for single crystals of perovskite-type manganese oxides. Description of the electronic phase diagram; Field-induced melting of charge-ordered state; Characteristics of magnetoresistance during transition changes.

Presents a study that examined the quasi-epitaxial growth of vaccum-deposited films of diacetylenes on various substrate including uniaxially aligned polymer surfaces formed with rubbing treatment or Langmuir-Blodgett technique. Background on organic polymers; Chemical properties of diacetylene monomers; Scanning electron micrographs of polydiacetylene films.

Presents a study that investigated the effect of nitrogen introduction on the photoconductivity of magnetron sputtered hydrogenated amorphous silicon carbon alloy films. Effect of nitrogen on the compositional and structural properties of the thin films; Analysis of the optical and electrical properties of the thin films; Influence of nitrogen on the optoelectronic properties of the thin films.

We report the ultrafast switching of the magnetic state in the course of photoinduced phase transition from an insulator with short-range charge and orbital order (CO/OO) to a ferromagnetic metal in perovskite-type Gd0.55Sr0.45MnO3. The femtosecond Kerr rotation and reflectivity measurements, which detect the spin and charge dynamics, respectively, have revealed that the metallic state is formed within the time resolution (∼200 fs); however, magnetization increases with the time constant of 0.5 ps. The relatively slow increase of the magnetization is attributable to the magnetic-field-induced alignment of ferromagnetic domains in the initially produced metallic state. [ABSTRACT FROM AUTHOR]

Optical three-photon difference frequency generation (DFG) was observed in Pr[sub 1-x]Ca[sub x]MnO[sub 3] (x = 0.30, 0.40) and Nd[sub 1-x]Sr[sub x]MnO[sub 3] (x = 0.48, 0.50). In the paramagnetic phase, the DFG signal reflects the fourfold anisotropy of the quasicubic crystal, and all the independent tensor elements for DFG near 2.0 eV are determined. Below T[sub N] ≈ 150 K, a two-order-parameter coupling to both antiferromagnetism and charge ordering leads to additional DFG contributions which allow to observe the formation of ∼100 µm large magnetic domains. [ABSTRACT FROM AUTHOR]

Perovskite manganite Pr[sub 0.65]Ca[sub 0.21]Sr[sub 0.14]MnO[sub 3] prepared as single crystal and ceramic specimens have been studied using magnetic, transport, and thermal measurements. All samples are identical metallic ferromagnets with T[sub C] = 204 K, nonetheless, unusual thermal hysteresis of magnetic susceptibility, electrical resistivity, and thermoelectric power were observed for polycrystalline samples. In connection with the critical proximity of the Pr[sub 0.65]Ca[sub 0.21]Sr[sub 0.14]MnO[sub 3] ferromagnet to an antiferromagnetic charge-ordered insulator suggests a link between the magnetic and transport behavior and phase instability and/or phase separation. We surmise more macroscopic phase separation in ceramics with the minor insulating phase associated with, or directly segregated in, the integrain regions whereas in a single crystal microscopic effects or dynamic phase fluctuations may occur. [ABSTRACT FROM AUTHOR]

The electric transport properties of single-crystal and ceramic samples of Pr[sub 1-x]Sr[sub x]MnO[sub 3] perovskites were investigated and correlated with structural and magnetic data. Analysis of the experimental data leads to the following conclusions: (i) the phase boundary between the ferromagnetic and A-type antiferromagnetic ground states is observed at x=0.49, (ii) the A-type systems are polaronic conductors in two dimensions, i.e., in the ferromagnetic planes, and approach the metallic conductivity with increasing x, (iii) an appreciable CMR effect in medium fields is observed for x∼0.50 due to the field-induced ferromagnetic transition, (iv) the A type-C type phase boundary occurs for x∼0.60, and, finally, (v) the charge carrier transport in the C-type antiferromagnets is reliably characterized by variable range hopping in one dimension i.e., along the ferromagnetic chains. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Single crystals of R[sub 1/3]Sr[sub 2/3]FeO[sub 3] (R=Pr, Nd, and Sm) were synthesized by the floating zone method and their magnetic properties and charge ordering (CO) transition related to lattice dynamics were systematically investigated. Mo¨ssbauer spectra of R[sub 1/3]Sr[sub 2/3]FeO[sub 3] were taken at various temperatures ranging from 12 K to room temperature. The charge disproportionation in Pr[sub 1/3]Sr[sub 2/3]FeO[sub 3] was detected below 190 K, in which two kinds of iron with valence states Fe[sup 3+] and Fe[sup 5+] were found with ratio of 2:1. The iron with valence state Fe[sup 4+] in Pr[sub 1/3]Sr[sub 2/3]FeO[sub 3] coexists at and above 150 K, and its ratio increased from 13% to 66% as the temperature rose. The (Nd[sub 1-y]Sm[sub y])[sub 1/3]Sr[sub 2/3]FeO[sub 3] (y=0.0, 0.2, 0.4, 0.6, and 0.8) with least lattice distortion underwent a CO phase transition at and below T[sub CO]=163 K and accompanying the charge disproportionation into nominally Fe[sup 3+] and Fe[sup 5+] sites as well as a canted antiferromagnetic spin ordering. In this charge ordering state, a sequence of Fe[sup +3]Fe[sup +3]Fe[sup +5]Fe[sup +3]Fe[sup +3]Fe[sup +5] exists aligned along the [111] direction of the pseudocubic perovskite structure. In this study, the CO at x=2/3 disappeared in the case of R=Sm. Indeed, disappearance of the CO transition was detected by systematic decrease of a spontaneous magnetization with increase of y in the system of (Nd[sub 1-y]Sm[sub y])[sub 1/3]Sr[sub 2/3]FeO[sub 3]. This result shows that the charge ordering state was realized with strong hybridization between the Fe and O atoms. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The heat capacity of single crystal La[sub 0.7]D[sub 0.3]MnO[sub 3], where D=Ca, Sr, has been measured through the Curie point in fields up to 70 kOe. The magnetic contribution of the Ca sample exhibits a sharp heat capacity peak at T[sub C]=218 K in zero field. The peak broadens and decreases in height with increasing field but, unlike an ordinary ferromagnet, the peak shifts substantially in temperature. As a consequence, the heat capacity data cannot be collapsed into a single scaling function. These features indicate that the transition is not an ordinary second-order ferromagnetic transition. Preliminary heat capacity data from the Sr-doped single crystal, with T[sub C]=360 K, do not exhibit the same shift in peak position with applied field. We attribute the difference in behavior between Ca- and Sr-doped samples to a change in the nature of the phase transition as T[sub C] lowers. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report that the incorporation of hydroxide ions (OH)- significantly enhances the superconducting transition temperature (Tc) in the LnFeAsO-based superconductors (Ln1111: Ln=La, Ce, and Pr). For La1111, Tc of the (OH)- incorporated sample synthesized using high-pressure technique becomes 35 K, which is higher by 7 K than the typical optimally doped La1111 superconductors. Similar enhancement in Tc is also observed for Ce1111 and Pr1111. 1H-NMR measurement have confirmed the existence of hydrogen atoms in the samples. Accompanying the (OH)- incorporation, the lattice parameters are largely contracted, down to the values which have never been attained by any other dopings/substitutions. [ABSTRACT FROM AUTHOR]

Imaging of charge/orbital ordering (CO/OO) structure and canted antiferromagnetic (AFM) domain structure in Sm1-xSrxMnO3 (x=0.55 and 0.6) has successfully been demonstrated. In the x=0.55 compound, the commensurate CO/OO structure with modulation vector Q=(0,1/3,0) was observed above the AFM transition temperature (TNA∼180 K). This modulation structure changes to an incommensurate one below TNA. In the x=0.6 compound, the typical 180° magnetic domains were observed in the (110) plane below 50 K indicating the canted AFM structure. This AFM structure locally collapses because of the existence of the short-range CO. [ABSTRACT FROM AUTHOR]

In situ observation of magnetic domain structures of Pr0.5Sr0.5CoO3 was made by Lorentz electron microscopy to reveal an unusual magnetic behavior around 120 K below the Curie temperature (TC∼220 K). The observations in a cooling run clearly showed that the magnetic domain structure changes below about 90 K and that the transformed domain structure remains unchanged down to 20 K. Furthermore, it was found that an electron-beam irradiation in an electron microscope induces a reversible transformation of the magnetic domain structure at 20 K. Possible mechanisms of such magnetic-domain structural changes are discussed. [ABSTRACT FROM AUTHOR]

The magnetization vector distribution at a cleaved surface of La[sub 0.7]Sr[sub 0.3]MnO[sub 3] (001) crystal has been quantitatively analyzed by using a newly developed low-temperature spin-polarized scanning electron microscope. The magnetic structure essentially consists of two kinds of domains, where magnetizations are parallel or antiparallel to the [110] direction with no surface-normal component. The rhombus-shaped domains range from a few to several tens of micrometers across. The domain structure can be considered to be made by laying down the magnetization from the out-of-surface-plane easy axis to the surface plane to reduce the magnetostatic energy without forming closure domains. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electric, thermal, optical, and magnetic properties have been investigated for ferromagnetic (ferrimagnetic) ordered double perovskites, A[sub 2]CrReO[sub 6] (A = Sr and Ca). Sr[sub 2]CrReO[sub 6] is found to be a metallic ferromagnet with a high Curie temperature (T[sub C]= 635 K), possibly the highest-T[sub C] half metal among the perovskite family. By contrast, Ca[sub 2]CrReO[sub 6] is a ferromagnetic Mott insulator with T[sub C] of 360 K. [ABSTRACT FROM AUTHOR]

Persistent ferromagnetic magnetization (M) as large as 0.6 μ[sub B] per Mn site can be induced by irradiating visible laser pulses on a thin film of 1% Cr-doped Pr[sub 0.5]Ca[sub 0.5]MnO[sub 3]. The enhancement of M upon the photoexcitation was also confirmed by the scanning superconducting quantum interference device microscope as an increase of magnetic field from ferromagnetic domains. The observed photoinduced transition from a metastable charge/orbital ordered state into a ferromagnetic one is likely to be assisted by the microscopic phase separation characteristic of such a relaxor ferromagnet as the present Cr-doped manganite. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Thin films of a magnetorelaxor compound, Pr[sub 0.5]Ca[sub 0.5]Mn[sub 1-y]Cr[sub y]O[sub 3] were grown on various substrates. Strain-free and polycrystalline thin films on MgO substrates well reproduce the properties reported for the bulk samples. Pseudomorphically strained and atomically smooth epitaxial thin films grown on perovskite substrates show strain-driven modification of the properties. Being consistent with the orbital ordering accompanied with charge ordering, tensile strain anomalously stabilizes the charge-ordered (CO) state. Compressive strain also suppresses ferromagnetism but high-Cr doping (y=0.10) induces magnetorelaxor behaviors, where the volume ratio of coexisting CO and ferromagnetic phases can be tuned and memorized by the history of the magnetic-field application. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies reflection spectroscopy on the local metallic phase of a crystal. Insulator-metal transition (IMT); Change of reflectivity due to the transition; Factors behind the different nature of the photoinduced IMT; Coverage of the modifications.

Investigates the magnetotransport properties of single-crystalline perovskite manganites. Exploration of optimized colossal magnetoresistance (MR); Enhancement of MR at a fixed nominal hole concentration; confirmation of the formation of single crystals by the back Laue reflection method.

Investigates the angular distribution of X-ray sheet beam from radioisotopes embedded in thin-film waveguide. Application of the non-energy-dispersive two-dimensional detector; Calculation of the optical electromagnetic wave solution of Maxwell equations; Relevance of upper 400 Angstrom gold on the intensity of the X-ray sheet beam.

We show a negative magnetoresistance (MR) in GaAs with magnetic MnAs nanoclusters (about 1.5% at 30 K in 1 T). The clusters were formed in a two step process consisting of the molecular beam epitaxy of (Ga,Mn)As layer and the subsequent annealing. The origin of the negative MR is attributed to the presence of the MnAs clusters. The mechanism is considered to be a spin-dependent scattering of carriers by MnAs clusters which decreases when the direction of the magnetization between the clusters aligns with the magnetic field. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In situ observation of magnetic domain structures of Pr0.5Sr0.5CoO3 was made by Lorentz electron microscopy to reveal an unusual magnetic behavior around 120 K below the Curie temperature (TC∼220 K). The observations in a cooling run clearly showed that the magnetic domain structure changes below about 90 K and that the transformed domain structure remains unchanged down to 20 K. Furthermore, it was found that an electron-beam irradiation in an electron microscope induces a reversible transformation of the magnetic domain structure at 20 K. Possible mechanisms of such magnetic-domain structural changes are discussed. [ABSTRACT FROM AUTHOR]

We report the ultrafast switching of the magnetic state in the course of photoinduced phase transition from an insulator with short-range charge and orbital order (CO/OO) to a ferromagnetic metal in perovskite-type Gd0.55Sr0.45MnO3. The femtosecond Kerr rotation and reflectivity measurements, which detect the spin and charge dynamics, respectively, have revealed that the metallic state is formed within the time resolution (∼200 fs); however, magnetization increases with the time constant of 0.5 ps. The relatively slow increase of the magnetization is attributable to the magnetic-field-induced alignment of ferromagnetic domains in the initially produced metallic state. [ABSTRACT FROM AUTHOR]