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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]

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]

Effects of vacancy on the microstructural and magnetic properties in self-doped LaMnO manganites have been studied. The samples crystallize in a single phase of rhombohedral structure exhibiting RC space group until -value reaches 0.2. As self-doped concentration increases, structural distortion is confirmed by combining X-ray diffraction. Ferromagnetic (FM) and antiferromagnetic (AFM) coupling is found and exchange bias effect appears at low temperature. Ferromagnetic diffuse phase transition (FDPT) is induced by Griffiths phase for at temperature of . The FM transition temperature range is increased from 32 K to 150 K. The enhancement of Griffiths phase with for is explained by the greater -site spatial disorder and the structural distortion. [ABSTRACT FROM AUTHOR]

In this article, the precursors of CaCuxMn3-xMn4O12(x = 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4) were synthesized using wet-chemistry technique, and then samples were sintered in pure oxygen flow at 850°C and ambient pressure with KCl 10 wt% addition. The Rietveld refinements of powder X-ray diffraction patterns showed that all the samples were single phase with cubic symmetry, the space group ${\rm Im}\bar{3}$. The lattice parameters a decreased with increasing Cu doping level x. The transport properties were characterized with DC four-probe technique. The results indicated that the crystal structure of samples were deformed and then influenced the transport properties of these manganese oxides. The MR ratios at 85 K and in the magnetic field of 5 Tesla increased with increasing x and reached the maximum at x = 1.0, then decreased with further increasing x. These results originated maybe from the intergrain tunneling of spin-polarized carriers and double-exchange effect. [ABSTRACT FROM AUTHOR]

In this paper, with solid source molecular beam epitaxy technique, Si1-xGex(SiGe) virtual substrates were deposited on low-temperature-grown Si (LT-Si) buffer layer, which was doped with Sb. The strain in SiGe virtual substrate was characterized by high resolution X-ray diffraction. Results indicated that Sb-doping in LT-Si can effectively modulate the degree of strain relaxation in SiGe virtual substrate. The segregated Sb on the surface of LT-Si layer acts as surfactant and results in abrupt strain relaxation. [ABSTRACT FROM AUTHOR]

Two series of NiO-Co-Cu-Co based spin valves with the same nominal structure were grown by the magneton sputtering technique with different deposition parameters. Texture, surface and interfacial microstructures and the magnetic properties have been investigated in detail. X-ray diffraction, grazing incident X-ray reflectivity and transverse X-ray diffuse scattering were combined to analyze the microstructure of the multilayers. The results show that the texture of the multilayers is not a prerequisite factor for an exchange-bias (EB) field in NiO/Co/Cu/Co spin valves. And the EB effect is also independent of the average roughness at the interfaces. Large correlation lengths and two dimensions of the roughness at the interface are more advantageous for the EB effect. [ABSTRACT FROM AUTHOR]

Highly epitaxial thin films of YBa2Cu3Oy (YBCO) have been successfully grown on Si using a double buffer of Eu2CuO4 (ECO)/(yttrium-stabilized zirconia) YSZ. The severe reaction between Si and YBCO is blocked by YSZ, and the crystallinity and superconductivity of the grown YBCO due to the lattice mismatch between YBCO and YSZ are improved by the ECO layer. The grown films were characterized by high-resolution X-ray diffraction, grazing incidence X-ray reflection, scanning electron microscopy (SEM), and Doppler broadened annihilation radiation spectroscopy, respectively. Very clear interfaces were found at YBCO/ECO/YSZ boundaries without any intermediate layer. The YBCO film surface was more smooth and stable. The results obtained indicate that highly epitaxial YBCO thin films can be successfully grown on Si wafers, demonstrating advantages of such a double buffer structure. [ABSTRACT FROM AUTHOR]

Effects of Si3N4 passivation layer on the lattice strain of Al0.22Ga0.78N layer with the thickness of 100 nm has been studied by in situ X-ray diffraction by the temperature range of 25°C–550°C. Results show that the temperature dependence of the strain relaxations can be separated into three linear regions. After passivation, an additional in-plane tensile strain is observed. The residual tensile strain increases with increasing temperature at low temperature, while at higher temperature the residual tensile strain decreases slightly. There is clear influence when a passive layer is deposited on the surface of the heterostructures. The linear regions in the temperature dependence of strain vary after the passive layer deposited on the heterostructure. These results indicate that the variation of the lattice strain relates to the difference in thermal stability between the epitaxy layer and the substrate. [ABSTRACT FROM AUTHOR]

SrTiO3 films are fabricated on DyScO3 substrates by pulse laser deposition. In situ X-ray diffraction (XRD) is used to characterize the thermal expansion coefficient at low temperature. The abnormal behavior in lattice parameter at 80 K may be the hint of a phase transition. High resolution XRD is performed to detect the two kinds of dislocations, i.e. screw and edge. Results show that the density of edge dislocation is a little larger than that of the screw one. The total dislocation density has the order of about 108 cm-2. Edge dislocation density decreases with the increase of the film thickness. We argue that the ratio between these two dislocation densities results in the growth mode of the film. [ABSTRACT FROM AUTHOR]

The composition of Mn0.05Si0.95 polycrystalline films on (001) Si substrate are prepared by vacuum deposition and post-crystallization processes. X-ray diffraction studies indicate that there are two phases coexist in the film: tetragonal, Mn4Si7 and diamond-like Si (Mn). The content of Si(Mn) phase increases with increasing the post-annealing temperature. Temperature dependence of the magnetization shows that there are two ferromagnetic phases with Curie temperature of around 50 K and near room temperature, which is confirmed by x-ray magnetic circular dichroism (XMCD). [ABSTRACT FROM AUTHOR]

Modulation-doped Al0.22Ga0.78N/GaN heterostructures with various thickness of Si-doped Al0.22Ga0.78N barrier (n-AlGaN) were deposited on (0001)-oriented sapphire (α-Al2O3) by atmosphere-pressure metal-organic chemical vapor deposition (MOCVD). The reciprocal space mappings (RSMs) of symmetric reflection (0002) and asymmetric reflection [Math Variable] were measured by means of the high resolution X-ray diffraction (HRXRD). The results indicate that the microstructures and the strain status of the n-AlGaN barrier correlate to those of the underlying i-GaN layer. The strained n-AlGaN barrier starts to relax when its thickness is 75 nm. It is found that there exists an "abnormal" relaxation state (the strain parameter γ>1) in modulation-doped Al0.22Ga0.78N/GaN heterostructures, which maybe results from the internal defects in Al0.22Ga0.78N barrier and the strain relaxation status at the i-GaN/α-Al2O3 interfaces. [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]

Single phase of La1−xSrxCoO3 (LSCO) with 0.1 ≤ x ≤ 0.4 have been prepared by the solid-state reaction method. All samples have the R3̅c symmetry. There is no phase transition detected at the temperature range from 10 to 300 K. The variations of the local bond-lengths of Co—O in CoO6 octahedron and lattice parameter ar confirm that hole-doping stabilize the intermediate-spin (IS) state of Co ions. The magnetic phase diagram is well understood in terms of phase separation scenario. Qualitatively, hole-rich ferromagnetic (FM) clusters increasing in size and number with the increase in the concentration of Sr at the expensive of non-FM insulating matrix, and percolating at the vicinity of 0.15, are suggested to explain the onset of FM order and insulator–metal transition. In addition, the values of effective paramagnetic moment μeff also strongly prove the presence of IS spin state of Co in our system. Very small magnetoresistance (MR), 5% with 3 T magnetic field applied, is obtained. This MR response indicates that a distinct mechanism is likely to dominate in LSCO compared to that in mixed-valence manganites. [Copyright &y& Elsevier]

In this article, the precursors of CaCuxMn3-xMn4O12(x = 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4) were synthesized using wet-chemistry technique, and then samples were sintered in pure oxygen flow at 850°C and ambient pressure with KCl 10 wt% addition. The Rietveld refinements of powder X-ray diffraction patterns showed that all the samples were single phase with cubic symmetry, the space group ${\rm Im}\bar{3}$. The lattice parameters a decreased with increasing Cu doping level x. The transport properties were characterized with DC four-probe technique. The results indicated that the crystal structure of samples were deformed and then influenced the transport properties of these manganese oxides. The MR ratios at 85 K and in the magnetic field of 5 Tesla increased with increasing x and reached the maximum at x = 1.0, then decreased with further increasing x. These results originated maybe from the intergrain tunneling of spin-polarized carriers and double-exchange effect. [ABSTRACT FROM AUTHOR]