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The double-wave method is widely used in ferroelectric measurements to eliminate the effects of conductance and capacitance components while preserving the ferroelectric domain contribution. However, in polycrystalline ferroelectric material, the assumption of the evolution of domains by the double-wave method no longer applies due to the domain back switch of de-field, and the domain contribution calculated by the current subtraction method is also problematic. Therefore, we proposed a new method to calculate the charge contribution of conductance and eliminate the conductance interference in the hysteresis loop. Finally, the feasibility of this new method is verified in many typical polycrystalline ferroelectric materials. This work provides a path for the study of ferroelectric properties of some high conductivity materials. [ABSTRACT FROM AUTHOR]

Hexagonal yttrium manganite (YMnO3) and chromium doped yttrium manganite (YMn1 – xCrxO3) were prepared by the solid-state method. X-ray diffraction and Raman scattering were combined to explore the structural characterization. Structural analysis illustrates that the lattice is compressed and the tilt of the MO5 (M = Cr or Mn) bipyramid is decreased with an increase in Cr3+ concentration, leading to declining frustration. Magnetic measurement suggests both weak ferromagnetic (FM) and antiferromagnetic (AFM) orderings enhanced with the growth of doping concentration. Enhanced weak FM ordering may arise from breaking of the superexchange interaction and introduction of the double-exchange interaction inside the layers, and the increased AFM ordering is attributed to the improved coupling between neighboring planes that resulted from the structural distortion. Spin-phonon coupling is discussed to confirm the enhanced coupling between interplane Mn3+ moments. [ABSTRACT FROM AUTHOR]

Laser-induced femtosecond demagnetization, femtomagnetism, offers a potential route to develop faster magnetic storage devices. It is generally believed that the traditional spin-wave theory, which is developed for thermally driven slow demagnetization, cannot explain this rapid demagnetization by design. Here, we show that this traditional spin-wave theory, once augmented by laser-induced spin–orbit torque, provides a highly efficient paradigm for demagnetization, by capturing low-energy spin-wave excitation that is absent in existing mechanisms. Our paradigm is different from existing ones but does not exclude them. Microscopically, we find that optical spin–orbit torque generates massive spin waves across several hundred lattice sites, collapsing the long-range spin-spin correlation within 20 fs. Our finding does not only explain new experiments but also establishes an alternative paradigm for femtomagnetism. It is expected to have far-reaching impacts on future research. [ABSTRACT FROM AUTHOR]

A series of polycrystalline YMn1-xRuxO3 (0≤x≤0.2) samples were prepared by traditional solidstate reaction method. Effects of doping on the microstructures and magnetic properties were investigated. Microstructural results reveal that samples crystallize in a single hexagonal structure with P63cm group for x≤0.1. Lattice parameters a, c, and unit-cell volume of YMn1-xRuxO3 are found to increase with doping content, which are ascribed to the larger radius of Ru3+ than that of Mn3+. Weak ferromagnetism is found and is enhanced with increasing doping concentration x. The bond angles of Mn-O3-Mn and Mn-O4-Mn are changed in the opposite trends, which break the Mn-Mn exchange interaction, thus the antiferromagnetic ordering. The MnO5 bipyramid is found to be relieved and the trimerization of Mn ions is weakened. These structural modifications result in the increase of weak ferromagnetism ordering in samples. [ABSTRACT FROM AUTHOR]

The structural, electronic, and magnetic properties of (La2/3Sr1/3MnO3)m/(SrRuO3)n superlattices have been investigated based on the first principles calculations. An obvious Jahn-Teller distortion, which depends on m, n, appears in MnO6 octahedron in the superlattices. The stretch along c-axis of MnO6 octahedron at the interface lifts the Mn eg orbital degeneracy, with electrons preferring the lower energy 3z2 - r2 to the higher energy x2 - y2. Benefitting from the charge transfer at the interface, the still occupied x2 - y2 orbital can mediate a robust in-plane double exchange interaction. La2/3Sr1/3MnO3 block is ferromagnetic and metallic, even for the superlattice with m=n=1. [ABSTRACT FROM AUTHOR]

LaMnO3+δ films with various thicknesses were grown on LaAlO3 (001) single crystal substrate to investigate the effect of in-plane compressive strain (~-0.57%) on magnetic properties. All films exhibit a blocking temperature Tb at which the zero field cooled magnetization reaches a maximum, indicating the ferromagnetic (FM) nanoclusters are embedded in the background of antiferromagnetic (AFM) matrix. The onset temperature of FM transition Tc and Tb is increased by 24% and 89%, respectively, with the thickness decreasing from 82.4 nm to 9.2 nm. Simultaneously, the saturation magnetization greatly increases by 309%, which is ascribed to the strain-induced transition of AFM to FM phase due to the orbital order structure switching from x²- 1/y²-1 [A-type] to (x²- y²) + (z²- 1) [F-type]. [ABSTRACT FROM AUTHOR]

This paper reports the effects of substrate-induced strain on the high-quality La0.5-xDyxCa0.5-ySryMnO3 (0≤x≤0.2) (LDCSMO) films grown on (00l) SrTiO3 (STO) substrate. LDCSMO films were epitaxially grown on the STO substrate along [001] direction. The lattice parameter c of the film increases relatively with the thickness increasing, and the in-plane tensile strain was controlled by varying the film thickness. The Raman results at room temperature show that the in-plane Mn-O bond stretching and MnO6 distortion were suppressed by the in-plane tensile strain with the thickness of film decreasing. The magnetic results show that the CO-AFM insulating phase and the weak FM phase coexist at low temperature, and spin-glass effect was found in all films. The ferromagnetic order and insulating state were enhanced by tensile strain in thinner film. This abnormal enhancement of insulating state may be ascribed to the disordering state due to the stronger FM and AFM competition and the dominated "dead layer" in thinner film. The improved FM ordering is resulted from the increased double-exchange interaction for the MnO6 distortion suppressed by the in-plane tensile strain in thinner film. These results indicate spin-phonon coupling could be manipulated by controlling strain in manganese oxide films. [ABSTRACT FROM AUTHOR]

In this report, we discuss the 22% efficiency improvement of solar cells based on the MAPbI3 perovskite film extracted with a mixed anti-solvent. The film quality of MAPbI3 extracted from the mixed anti-solvent of ether and isopropanol is improved greatly. The average grain size of the film may be enlarged twice. We argue that some solvents residing in the precursor may effectively promote the crystallization process of MAPbI3 to form large grains. We believe that this study may open a method to fabricate high-quality MAPbI3 perovskite films for highly efficient solar cells. [ABSTRACT FROM AUTHOR]

Perfect and defective surface structures for (001) SrTiO3 are determined in considering a supercell with 11 atomic layers using the first-principles calculations. The amplitude of the surface rumpling for the SrO-terminated surface is much larger than that for the TiO2-terminated surface, although both SrO- and TiO2-terminated surfaces are stable for a comparable range of the TiO2 chemical potential. The distance between the first and second planes compresses while that of the second and third planes expands due to the relaxation of the slab. The top sites of the oxygen atoms of SrO-termined surface and the fourfold symmetry hollow sites of TiO2-termined surface are favorable for Ti or Sr adsorbate. The relative stability of the defect species or reactions varies with the equilibrium conditions. The dominant surface defect is Ti substitutional defect and a TiO–TiO2 double layers may form at the surface, which has been confirmed by experiments. [ABSTRACT FROM AUTHOR]

Polycrystalline Si1-xMnx thin films codoped with boron have been fabricated by sputtering technique followed by postcrystallization processes. Structural, magnetic, and transport properties of the films were investigated. Magnetic property investigation indicated that the films consist of two ferromagnetic phases. The low Curie temperature ferromagnetic phase (TC∼50 K) is due to the Mn4Si7 phase in the films as detected by x-ray diffraction, while the high temperature one (TC∼250 K) is resulted from the incorporation of Mn into silicon. It has been found that, with carriers confirmed as p type, for the same effective concentration of Mn the saturation magnetization of the films with higher carrier concentration is higher than that of those with lower carrier concentration, which suggests a mechanism of hole-mediated ferromagnetism for Si-based diluted ferromagnetic semiconductors. [ABSTRACT FROM AUTHOR]

The influence of a nano-nitride-layer (NNL) doped at different interfaces in the structure of Cu/Co/Cu/Co/Cu on magnetoresistance (MR) is investigated. As the NNL is doped at the inner interfaces of the core Co/Cu/Co sandwich, an inverse MR is observed. This contrasts sharply with that doping at the two outer interfaces between the core sandwich (Co/Cu/Co) and the buffer or/and the capping layers. The result arises from the negative spin asymmetry induced by the NNL doping under different interfacial circumstances. Moreover, the MR value increases in magnitude as temperature is decreased from room temperature to 4.2 K. [ABSTRACT FROM AUTHOR]

Multilayers of [Co/Pt]20, with tCo/tPt≐7 and the period Λ in the range of 0.27–0.69 nm, and [Co(0.46 nm)/Pt(0.07–0.14 nm)]20 have been prepared by sputtering at low deposition rates and a high Ar pressure of 7.8 Pa. Structure and magnetic properties were characterized by x-ray diffraction, transmission electron microscopy, magnetometry measurements, and magnetic force microscopy. Column structure, coherent stacking of Co and Pt layers, and small grains have been observed. The average atomic interplane distance d111 changes with the constituent layer thickness. In the first series of Co/Pt multilayers, the out-of-plane coercivity gradually increases to reach a maximum, with the bilayer period increasing from 0 to 0.58 nm, and decreases with further increasing period. For the second series, the out-of-plane coercivity increases to reach a maximum of 6.5 kOe with tPt increasing from 0.07 to 0.13 nm and decreases with further increasing tPt. In order to explain the strong magnetic perpendicular anisotropy, the magnetoelastic energy of CoPt alloy layers must be taken into account. [ABSTRACT FROM AUTHOR]

Describes the application of thin silicon (Si) films for selective area Si and zinc (Zn) diffusion into gallium arsenide and AlGaAs. Advantage of the Si film; Details on the Zn diffusion with the Si mask.

A pure compressively strained La2/3Ca1/3MnO3 (LCMO) dead layer grown on (001)-oriented LaAlO3 substrate can show all the rich phenomenon of large bias field shift, coercive field enhancement, and high blocking temperature. The obtained exchange bias field (~350 Oe) and the enhanced coercivity of about 1160 Oe at 5K under 500 Oe cooling field are superior to that have been reported in LCMO-based ferromagnetic/antiferromagnetic superlattices or nanoscale systems. Our results clearly demonstrate that the inhomogeneous magnetic dead layer of LCMO can induce a strong exchange bias effect, which may be exploited as a very simple structure for spin-valve device application. [ABSTRACT FROM AUTHOR]

The self-doped La1-xMnO3 (x=0.1 and 0.3) thin films deposited on Nb-doped (wt % y) SrTiO3 (y=0.05 and 0.8) crystals to form heteroepitaxial junctions have been prepared by the pulse laser deposition method. The current-voltage loops of junction were measured at several fixed magnetic fields for the temperature from 10 to 300 K. We have focused on the effects of doping level and annealing time on the magnetically tunable property of the junction. The results show that these junctions have a typical temperature-dependent rectifying characteristics and asymmetrical hysteresis. The magnetically tunable property of the junction was related with the annealing time for the self-doped La1-xMnO3-δ thin film and the doping level in the Nb-doped SrTiO3 (STON) crystal. In the self-doped La0.9MnO3/0.05-STON junction annealed at 900 °C for 5 h, the relative ratio of voltage [Vb(0)-Vb(H)]/Vb(0) is about 70% at H=6 T and T=70 K for I=0.1 mA, showing a large magnetically tunable property. These results reveal the great potential of the manganites in configuring artificial devices. [ABSTRACT FROM AUTHOR]

Effects of cation disorder and strain on the surface morphologies and transport properties of thin films with different A-site cation disorder, which was achieved by Y and Sr codoping into La2/3Ca1/3MnO3, have been investigated. A metal-insulator transition (MIT) was observed on all films except that on MgO, which indicates that large strain increases insulator phase. With increasing cation disorder, the resistivity increases while MIT and Curie temperature decrease, which reveal that cation disorder suppresses the long-range ferromagnetic metallic phase. The spin-glass state and ferromagnetic-metallic state coexist in low temperature. Cation disorder induces more insulator phases in the large strain films. A Kondo-like transport behavior was observed in the large cation disordered films. [ABSTRACT FROM AUTHOR]

Structural and magnetocaloric properties for the perovskite manganite La2/3-xYxCa1/3-ySryMnO3 (x<0.2) have been studied. These compounds with the fixed A-site average ionic radii of 1.204 Å and Mn4+/Mn3+ ratio were prepared by conventional solid-state reaction technique. The lattice parameters were obtained from refining x-ray diffraction diagrams preformed by Rietveld refinement method. The ferromagnetic ordering temperature TC increases abruptly owing to the increase in the competition between A-site size-disorder degree σ2 and double-exchange interaction resulting from Mn–O–Mn bond angle. Phase transition may be broadened due to the cation disordering at A-site. Sample with x=0.01 appears a large magnetic entropy ΔSM=3.3 J kg-1 K-1 at the Curie temperature TC=274 K, which may be used as a promising candidate for magnetic refrigerant near room temperature. [ABSTRACT FROM AUTHOR]

Single phases of double layered perovskitelike Sr2-xGdxFeMoO6 samples with x varying from 0.00 to 0.25 have been synthesized. Distortion in FeO6 and MoO6 octahedrons is characterized by Rietveld refinements using the powder x-ray diffraction data. Antisite defects are considered during the refinements. Positron annihilation spectroscopy shows us that the density of antisite defects increases with increasing x. The size of defects reaches the largest values, and conducting electrons are most extensive in sample with x=0.20. The insulating behavior is observed. We argue that the valence states between Fe and Mo play the critical role in magnetism and transition properties in Gd doped Sr2FeMoO6. [ABSTRACT FROM AUTHOR]

La2/3Ca1/3MnO3 (LCMO)/YBa1.8Eu0.2Cu3O7 (YBECO) multilayers on yttrium-stabilized ZrO2 are fabricated. YBECO sublayer is well crystallized in c-axis orientation, while LCMO sublayer crystallized in (001) textured structure, which forms special mosaic structure. By magnetization measurements, we confirm that the cluster spin glass existed in LCMO/YBECO multilayers in low temperature, which may scatter the transport electrons. Superconductivity cannot be observed when thickness of YBECO layer is less than 24 nm. The magnetoresistance ratio depends on the thickness of YBECO layer. The magnetotransport properties of the multilayers make it very promising to provide a technological support for the heterostructure and superlattice of manganites and superconductors. [ABSTRACT FROM AUTHOR]

YBa2Cu3O7-δ (YBCO) powders with Gd2O3 additives are prepared by the solid state reaction method. X-ray diffraction with Rietveld refinements shows that both Gd2O3 and YBCO phases coexist in the products. With increasing additive content, the unit cell symmetry of YBCO phase remains unchanged but the grain size increases. The critical current density (Jc) exhibits a maximum at x=0.1 in YBCO+ xGd2O3 systems. Moreover, the addition of Gd2O3 in YBCO enhances Jc by applying the magnetic field, although the superconducting temperature (Tc) decreases slightly. We argue that the characteristic behavior of Jc may come from the counterbalance of two effects simultaneously, which was caused by the variation of superconductivity and the inhomogeneity of grain distribution in nanoscale. [ABSTRACT FROM AUTHOR]

Giant magnetoresistance (GMR) and tunnel magnetoresistance (TMR) were studied in spin valves of FeCo/Cu/(FeCo)1-xGdx and magnetic tunnel junctions of FeCo/AlO/(FeCo)1-xGdx, respectively. When the FeCoGd layer is thick enough, both GMR and TMR ratios change their signs from positive to negative at the compensation composition with 0.293<=x0<=0.337 as the Gd content is increased. This scenario is originated from a competition of rare-earth and transition-metal spins in FeCoGd layers with antiferromagnetic coupling. Accordingly, it is deduced that in the FeCoGd layer the spin polarizations PN of electrons at the Fermi level and tunneling spin polarization PTSP are negative and positive for x0, respectively, and vice versa for x>x0. [ABSTRACT FROM AUTHOR]

As a new signature, the hysteretic behavior of angular dependence of exchange bias in FeNi/FeMn bilayers is studied as function of the constituent layer thickness. When the FeMn layer is thin enough, there is no hysteretic behavior. When the FeMn layer thickness is increased, the hysteretic effect reaches a maximum sharply and then decreases slowly as the FeMn layer thickness is further increased. It is independent of the ferromagnet layer thickness. This new phenomenon implies a thermally driven evolution of the magnetic state in the antiferromagnet layer. [ABSTRACT FROM AUTHOR]

Structure and transport properties of Eu-doped YBa2-xEuxCu3O7-δ (YBECO) have been studied. Eu is confirmed preferring to replace Ba at Ba sites. The averaged valence state of Eu, which is examined by x-ray photoemission spectroscopy, increases with increasing x. Eu doping in YBECO has a little influence on superconductivity in our studies, and the superconducting transition temperature Tc is almost unchanged. [ABSTRACT FROM AUTHOR]

We introduce enhanced hybridization of Ti 3d-O 2p electronic states by applying an inhomogeneous electric field to a perovskite oxide, SrTiO3, which leads to lattice deformation through electrostriction and the converse flexoelectric effect. However, unlike most studies revealing lattice responses to dipolar polarization, the enhanced electronic hybridization introduced in SrTiO3 is not strong enough to compensate local repulsions and gives rise to the off-centered Ti displacement. This is consistent with the fact that SrTiO3 has a small vibronic coupling constant compared to other ferroelectric materials. In situ time-dependent X-ray diffraction studies reveal lattice relaxation. Band structures and electronic hybridization play important roles in lattice relaxation, which is different from the relaxation of metals where the carrier concentration may be dominant. Our results provide insight into the coupling behaviors between the lattice and electronic hybridization, considering both static and dynamic aspects. [ABSTRACT FROM AUTHOR]

Epitaxial orthorhombic YMn0.9Ru0.1O3 films with different thickness have been grown on (001)-SrTiO3 substrates by pulsed laser deposition (PLD). The crystal structure is well investigated by X-ray Diffraction. It is found that the out-of-plane parameter c slowly increases with decreasing thickness of samples because of the tensile strain between the films and substrates along c axis. The lengths of in-plane Mn-O bonds expand with the enhancement of strains, which is proved by Raman scatting. The magnetic measurements reveal that there exist two magnetic transition temperatures TN1 and TN2. The TN1 is close to that of orthorhombic YMnO3 bulk. With decreasing thickness of the films, TN1 keeps almost constant because of the small stain along c-axis. TN2, however, obviously increases from 117 K to 134 K, which could be related to the expansion of in-plane Mn-O bonds. Results show that the magnetic transition temperature of YMn0.9Ru0.1O3 films can be sensitively manipulated by the strain of the films. [ABSTRACT FROM AUTHOR]

For Gd45Fe55/Fe50Mn50 bilayers, both negative and positive exchange biasing have been observed for low and high magnetic cooling field HCF, respectively. These results can be attributed to a competition between antiferromagnetic coupling at GdFe/FeMn interface and the Zeeman energy of FeMn spins under HCF. In order to reveal the magnetization reversal mechanism, the angular dependence of HE and HC has been investigated. It is found that the negative exchange biasing and the positive one have similar angular dependence that can be described by a magnetization coherent rotation model. [ABSTRACT FROM AUTHOR]

We studied the microstructures, electronic, and magnetic properties on La-doped and La- and Ca-codoped YBa2Cu3O7-δ (YBCO). The superconducting transition temperature remains unchanged up to 10% for La-doped YBCO. The competition between electrons and holons was assumed according to the variation of Tc0 in La and Ca codopings in YBCO. The magnetoresistance (MR) effect is about 8%, which is observed obviously near the critical temperature and is independent of the content of La in La-doped YBCO. MR increases up to about 40% with the incorporation of Ca in La-doped YBCO. We present here possible explanations for the magnetoresistance effect in polycrystalline samples based on the microstructure and the increase of oxygen vacancies at grain-boundary interface. [ABSTRACT FROM AUTHOR]

We have observed that the extraordinary Hall resistance of Pt/Co/Pt sandwich with perpendicular magnetic anisotropy changes from positive to negative drastically as the current density increases in an applied field, indicating the magnetization switching induced by the current. There exists a critical current density that changes for the different applied field with the order of current density of 104 A/cm2, which is much lower than that reported in literatures on the current-induced magnetization switching. The results of the extraordinary Hall effect of the sample in different in-plane current density show that the magnetization-switching field decreases with the increment of current density when the current density is larger than 104 A/cm2. [ABSTRACT FROM AUTHOR]

Thin YBa2Cu3O7-δ/La0.67Ca0.33MnO3/YBa2Cu3O7-δ (YBCO/LCMO/YBCO) trilayers on (001)-oriented SrTiO3 (STO) substrates were fabricated by magnetron sputtering technique. The trilayers are well c-axis oriented confirmed by x-ray diffraction. The surface and interface structure of the trilayers were investigated by grazing incident x-ray reflectivity. The results showed that there exists diffusion at the YBCO/LCMO interfaces with the diffusion length of several nanometers. The root-mean-square (rms) roughness of surface and interface in the trilayers varied with the thickness of YBCO layer. The rms roughness of surface was consistent with observation by atomic force microscopy. A further analysis indicated that the rms roughness was correlative to the misfit strain relaxation in film. [ABSTRACT FROM AUTHOR]

The interface structure and magnetoresistance (MR) for the single spin valve (SV) of Co/Cu/Co structure with a NiO layer at the top or under the bottom were investigated. Glancing incident x-ray reflectivity and x-ray diffuse scatter studies show that the interface roughness of NiO on Co is much larger than that of Co on NiO. The large roughness may be one of the main factors of suppressing spin reflectivity. The interface between NiO and Co becomes more flat after annealing. Different temperature dependence of MR was observed for the top and the bottom SV. We attribute the above phenomena to the competition between the roughness and the exchange effects of the NiO/Co interface. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

La0.67Ca0.33MnO3 (LCMO) thin films with the thickness varying from 200 to 500 Å have been deposited by magnetron sputtering on sapphire, SrTiO3, yttrium-stabilized ZrO2 substrates. A metal-to-insulator transition behavior was observed for all samples with the transition temperature and width varying with the substrate and the film thickness. A percolation model has been used to obtain the physical parameters on low-temperature metallic transport behavior and the adiabatic thermal small polaron hopping progress. The surface of the deposited films was measured by atomic force microscopy and grazing incidence x-ray specular and diffuse scattering. Fits to the data show the presence of a mixed layer between the substrate and the LCMO films the extent of which depends on the substrate used. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Thin Yba[SUB2]Cu[SUB3]O[SUB7-δ/La[SUB0.67]Ca[SUB0.33]MnO[SUB3] (YBCO/LCMO) films were grown on SrTiO[SUB3](STO)substrates by magnetron sputtering technique. The microstructures of the bilayers were characterized and a standard four-probe technique was applied to measure the resistivity of the samples. The interdiffusions at the YBCO/LCMO and LCMO/STO interfaces formed two transient layers with the thickness of about 3 and 2 nm, respectively. All the bilayers were well textured along the c axis. At low temperature, the superconductivity can only be observed when the thickness of YBCO is more than 25 nm. When the thickness of YBCO is less than 8 nm, the bilayers show only ferromagnetism. The superconductivity and ferromagnetism perhaps coexist in the bilayer with the YBCO thickness of 12.5 nm. These interesting properties are related to the interaction between spin polarized electrons in the manganites and the cooper pairs in the cuprates. [ABSTRACT FROM AUTHOR]

Structural, magnetic, and calorimetric properties are reported for the La[sub 1-x]Pr[sub x]Ba[sub 2]Cu[sub 3]O[sub 7] solid solution. The structure remains orthorhombic with lattice parameter increases from a=0.3872, b=0.3927, and c=1.1709 nm for PrBa[sub 2]Cu[sub 3]O[sub 7] to a=0.3903, b=0.3944, and c=1.1801 nm for LaBa[sub 2]Cu[sub 3]O[sub 7]. Substitution of Pr for La depresses T[sub c] from 90 to 52 K for La[sub 0.5]Pr[sub 0.5]Ba[sub 2]Cu[sub 3]O[sub 7], which was reported to be a nonsuperconductor. The Pr antiferromagnetic ordering temperature T[sub N] decreases monotonically from 18 K for PrBa[sub 2]Cu[sub 3]O[sub 7] to 6 K for La[sub 0.8]Pr[sub 0.2]Ba[sub 2]Cu[sub 3]O[sub 7]. Thus there is a large range of coexistence of superconductivity and antiferromagnetism for 0.2≤x≤0.5. The superconductivity and anomalous Pr ordering will be discussed with the R[sub 1-x]Pr[sub x]Ba[sub 2]Cu[sub 3]O[sub 7] systems (R=Y, Nd-Lu). © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The compressive LaMnO3+δ thin films with thickness of ~20 nm are grown on LaAlO3 (001) single crystal substrates under various oxygen environment. With decreasing oxygen pressure, the in-plane compressive strain is enhanced. It is found that the breathing mode (Q1) and the basal plane distortion mode (Q2) of MnO6 octahedron are suppressed, while the octahedral stretching mode (Q3) is promoted. The promoted Q3 switches the orbital order from x2-1/y2-1 to (x2-y2)+(z2-1) type. The ferromagnetic (FM) transition temperature Tc increases from 85 K to 105 K and the low-temperature magnetization increases greatly by 175%. The abnormal enhancement of magnetization with decreasing oxygen pressure is ascribed to the strain enlarged FM domains due to the decreased MnO6distortion and the switched orbital ordering. This result is advantageous to explain the novel phenomena in LaMnO3-related systems. [ABSTRACT FROM AUTHOR]

Reports on a study which demonstrated the use of sputtered silicon films in developing etching masks for gallium arsenide devices. Materials commonly used for etching masks; Preparation of the silicon films; Conclusion.

The current-perpendicular-to-plane magnetoresistivity (CPP-MR)/ρc(B) is investigated in single crystal ruthenates Ca3(Ru1-xTix)2O7 (x=0.02). This material is naturally composed of ferromagnetic metallic bilayers (Ru,Ti)O2 separated by nonmagnetic insulating layers of Ca2O2, resulting in tunneling magnetoresistivity. Non-monotonic ρc(B) curves as well as the inverse spin valve effect are observed around the magnetic phase transition associating with the metal-to-insulator transition. A spin dependent tunneling model with alternate distribution of hard and soft magnetic layers [(Ru,Ti)O2] is proposed to explain the exotic CPP-MR behavior. This eccentric CPP-MR behavior highlights the strong spin-charge coupling in double-layered ruthenates and provides a potential material for spintronic devices. [ABSTRACT FROM AUTHOR]

The influence of AlN, Si3N4 and SiO2 surface-passivation dielectrics on high-temperature strain relaxation of AlGaN in AlGaN/GaN heterostructures was investigated in the range from room temperature to 600 °C by means of x-ray diffraction. The Si3N4 and SiO2 films produce an additional biaxial tensile stress to the underlying AlGaN barrier layer, whereas the AlN film produces an additional biaxial compressive stress. The authors found that the process of long-time heating and cooling results in a nonreversible lattice relaxation in the AlGaN layer. The passivation dielectrics used in this work can mitigate this high-temperature strain relaxation. The AlN dielectric manifested a better effect than the Si3N4 and SiO2 dielectrics. [ABSTRACT FROM AUTHOR]

The lattice strain distributions of epitaxial SrTiO3 films deposited on LaAlO3 were investigated by in situ x-ray diffraction at the temperature range of 25–300 K, grazing incident x-ray diffraction, and high resolution x-ray diffraction. The nearly linear temperature dependence of the out-of-plane lattice constant of SrTiO3 was observed in the measured temperature range. The depth distribution of the lattice strain at room temperature for SrTiO3 films includes the surface layer, strained layer, and interface layer. [ABSTRACT FROM AUTHOR]

The temperature dependence of strain relaxation in Al0.22Ga0.78N layers, with and without a Si3N4 surface passivation layer, was investigated at temperatures from room temperature to 813 K using high-resolution x-ray diffraction. A small strain relaxation occurs in the unpassivated Al0.22Ga0.78N layers at high temperature. After passivating, an additional in-plane tensile strain and an initial increase of the residual tensile strain with increasing temperature were observed in Al0.22Ga0.78N layers, and at higher temperatures the residual tensile strain only decreases slightly in the 100-nm-thick Al0.22Ga0.78N layer, but a pronounced strain relaxation occurs in the 50-nm-thick one. The degree of strain relaxation of the passivated 50-nm-thick Al0.22Ga0.78N layer increases by about 33%, which results in the two-dimensional electron gas concentration reduction of about 16% at the whole temperature range in our measurements. [ABSTRACT FROM AUTHOR]

Si/Ta/Co/Cu/CoFeMn (or NiO) spin valves were prepared by a delayed sputtering procedure, in which depositions of Ta and followed layers were intervened by 1 h. The spin valves are found to have better coherent growth with stronger (111) preferred orientations in Co and Cu layers, compared with the traditional continuous method. At the same time, the giant magnetoresistance ratio and spin-dependent scattering are enhanced by a factor of 20%–30%. These results indicate that the coherent growth and the (111) preferred orientation can enhance the spin-dependent scattering of spin valves. [ABSTRACT FROM AUTHOR]

The magnetic and electrical properties of crystalline Mn0.05Si0.95 films prepared by post-thermal treatment of the as-deposited amorphous Si-Mn (95 at.%-5 at.%) have been investigated. Both the temperature dependence and field dependence of magnetization were measured using superconducting quantum interference devices, and it has been indicated that the film materials are ferromagnetic with Curie temperature over 400 K. X-ray diffraction analysis revealed full crystallization of the films and the incorporation of Mn into the host crystalline Si lattice. Behavior of thermally activated conduction processes of the films has been evinced by electrical property measurement for the films. [ABSTRACT FROM AUTHOR]

We review the methods of calculating the effective energy Ueff(T,B,J) for both transport measurements and magnetic decay, and suggest a new resistivity expression that is compatible with both vortex glass theory and thermal assistant flux creep theory. Then we apply these methods in our HgBa2Ca2Cu3O8+δ single phase superconductor to obtain the activation energy. Transport results confirm that the magnetic field and temperature dependence of the Ueff(T,B) can be well described by our new model. Magnetic relaxation data shows that the current density dependence of Ueff(J) can be scaled onto a single curve following the vortex glass theory. The exponent obtained from the scaling law is 0.978 in the temperature range 4.2-60 K, close to the value of 7/9 in the regime of flux creep in large vortex bundles predicted by vortex glass theory. [ABSTRACT FROM AUTHOR]

(001)-oriented FePt films are deposited, by magnetron sputtering at 300 °C, on LaAlO3 (001), SrTiO3 (001), and MgO (001) single crystal substrates. The tetragonal distortion, magnetic anisotropy, and the coercive force of the films vary with the substrate. The ordering process is very different with the substrate, which may affect the magnetic properties of the film. The magnetic coercivity decreases with increasing the ordering parameter and the tetragonal distortion, which may be ascribed to the lattice strain. [ABSTRACT FROM AUTHOR]

Effects of local structural distortion on magnetization in BiFeO3(BFO) with Pr and Ba co-doping were systematically investigated. A structural phase transition of rhombohedral-to-cubic occurs in Bi0.75Pr0.15Ba0.1FeO3 sample. The strong enhancement of the spontaneous magnetization is significantly affected by the local lattice distortion and collapse of the spatial spin structure. Charge compensation is very possible while Pr4+ and Ba2+ replacing for Bi3+ together in BFO, which may suppress the charge defects and decrease the magnetism. [ABSTRACT FROM AUTHOR]

Crystal tilts in the epitaxial lateral overgrown (ELO) GaN region over SiO[sub 2] mask by hydride vapor phase epitaxial away from the opening region were investigated by scanning electron microscope and the four-circle x-ray diffraction method. The increased mask width and ratio of stripe opening width to stripe period (fill factor) lead to increased wing tilts. The introduction of additional HCl and C[sub 3]H[sub 8]/H[sub 2] can decrease wing tilts and improve the ELO GaN surface morphologies significantly. Moreover, it has been observed that a high growth rate will bring more defects and large wing tilts into the GaN materials. [ABSTRACT FROM AUTHOR]

The characteristics of novel reverse-biased waveguide phase modulators are reported. These devices, which use the translation of a depletion edge, have provided the highest efficiency figure of merit (56 °/Vmm) ever reported for a reverse-biased device. Furthermore, the speed of the device is only limited by the RC time constant. The investigated devices were GaAs/AlGaAs ridge waveguide modulators, a geometry which is well suited for integrated optoelectronics. [ABSTRACT FROM AUTHOR]

We studied the microstructures, electronic, and magnetic properties on La-doped and La- and Ca-codoped YBa2Cu3O7-δ (YBCO). The superconducting transition temperature remains unchanged up to 10% for La-doped YBCO. The competition between electrons and holons was assumed according to the variation of Tc0 in La and Ca codopings in YBCO. The magnetoresistance (MR) effect is about 8%, which is observed obviously near the critical temperature and is independent of the content of La in La-doped YBCO. MR increases up to about 40% with the incorporation of Ca in La-doped YBCO. We present here possible explanations for the magnetoresistance effect in polycrystalline samples based on the microstructure and the increase of oxygen vacancies at grain-boundary interface. [ABSTRACT FROM AUTHOR]

Silicon diffusion into AlxGa1-xAs (x=0–0.4) from a sputtered Si film is described. It is shown that both the diffusion rate and the surface concentration of Si decrease with increasing Al mole fraction. The diffusion behavior of Si in AlxGa1-xAs is discussed in terms of the binding energy of the Al–As bond and mixed crystal disorder. [ABSTRACT FROM AUTHOR]

The buried p-type conduction is demonstrated in InN with Ba ion implantation dose increases up to 1 × 1015 ions/cm-2. The in-plane lattice parameter increases by about 1.2% deep in the film due to larger Ba replacing smaller indium (In). The n-type conductivity is also detected at the surface, which may results from the N-deficiency. First-principles calculations show that holes at the surface, induced by Ba ion implantation, are compensated by extra electrons from the In adlayer. The p-type carriers dominate in the bulk layers, which is in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]