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The present study is focused on the investigation of the distorted tetragonal phase of mixed spinel oxides, due to their technological relevance in the field of electronics, spintronics, magnetism, catalysis, and electrochemical energy storage. Herein, we report on solgel synthesized multivalent cobalt manganites, CoMn2O4 (CMO), and subjected them to a comprehensive analysis to elucidate their physicochemical characteristics at room temperature. Analysis employing powder x-ray diffraction patterns and electron microscopy (including field-emission scanning electron microscopy and high-resolution transmission electron microscopy) results confirmed the formation of a pure and exceptionally crystalline, distorted tetragonal phase of mixed CMO. Synchrotron-based x-ray absorption spectroscopic (XAS) measurements in the total electron yield mode examined local electronic structures affirming the formation of CMO with uncompensated electronic states involving Co2+, Co3+, Mn2+, Mn3+, and Mn4+ cations. Concurrently, XAS and x-ray magnetic circular dichroism analyses revealed antiferromagnetic coupling within Co and Mn sublattices in CMO, indicating the presence of uncompensated electronic states. Vibrating sample magnetometry results demonstrated clear hysteresis behavior, explicitly indicating the coexistence of super-paramagnetic and canted antiferromagnetic characteristics in CMO, as validated through the Langevin function fitting and x-ray magnetic circular dichroism results. The noticeable absence of saturated magnetization confirmed the high degree of spin canting, primarily stemming from the presence of the Yafet–Kittel spin arrangement. [ABSTRACT FROM AUTHOR]

Spintronics-based studies have produced significant attention in the last decade while claiming the observation of room temperature ferromagnetism (RTFM). Nevertheless, there is a lack of consensus on a mechanism responsible for this phenomenon. In this study, we focus on Cu-doped ZnO (ZCO) to understand the microscopic origin of RTFM and the role of different oxidation states of Cu in RTFM. We have performed different spectroscopic techniques using synchrotron facilities. The values of spin-moment obtained from x-ray magnetic circular dichroism sum-rule truly exhibit a ferromagnetic interaction in the nanocrystalline powder of ZCO with ∼0.58 μB for 5% of Cu concentration in the total fluorescence yield mode. Such an enhanced magnetization is attributed to the presence of Cu2+, which is mainly localized in the bulk region. Cu in ZCO is mostly dominated by the presence of Cu2+. This is clearly reflected by the profiles of x-ray photoemission spectroscopy. Consequently, the weakly magnetized total electron yield mode is attributed to a state of magnetic frustration as the majority of Cu3+ is found on the surface. Some of these Cu3+ when come in the vicinity of Cu2+ ions result in a highly correlated state of double exchange mechanism, which is the microscopic origin of RTFM in ZCO. The coupling between Cu2+-Cu3+ is mediated via oxygen vacancies (VO), the presence of which is confirmed through the features of electron energy loss spectroscopy over different edges. The confirmation of VO is also supported by the deconvolution of E2high-phonon in the Raman spectra. Moreover, the defects in the local electronic structures of ZCO are demonstrated by the deconvoluted spectra of Cu L3 x-ray absorption spectroscopy. The images obtained from high-resolution transmission electron microscopy confirm the incorporation of Cu into the wurtzite crystal of ZnO. A clear enhancement in magnetization upon an increase in carriers of Cu in ZCO indicates carrier-induced ferromagnetism. Cu2+ and VO are the two attributes of RTFM in ZCO. [ABSTRACT FROM AUTHOR]

Abstract: Microstructure engineering provides an effective way to improve the vortex pinning via addition of nano precipitates in a superconducting matrix. Precise control of these nano precipitates, including their dimensions and alignment, is critical to obtain optimal pinning. DyBa2Cu3O7-x (DyBCO) films with BaZrO3 nano precipitates (BZO-NPs) were grown on biaxially-textured MgO buffer layers deposited by Inclined Substrate Deposition (ISD) on Hastelloy substrates. A critical current density (Jc) of 0.9 MA cm-2 was obtained at 77K in self-field. Orientation and size of the BZO-NPs were investigated using Transmission Electron Microscopy (TEM). The BZO-NPs were aligned along the (a,b)-plane of DyBCO and thus was greatly affected by the faceted geometry of the ISD MgO buffer layer. [Copyright &y& Elsevier]

Abstract: DyBa2Cu3O7-δ (DyBCO) films were grown on biaxially-textured MgO buffer layers deposited on Hastelloy substrates, typical critical current densities (Jc) were 2.1 MA cm-2 at 77K in self-field. Biaxial texturing and the orientation relationship of DyBCO films with respect to the Inclined Substrate Deposition MgO buffer layer were investigated using plan-view and cross-section Transmission Electron Microscopy (TEM). A detailed analysis of the microstructural parameters will be summarized. Despite the large lattice mismatch (8.5%) the DyBCO grows epitaxially on the MgO buffer layer and the biaxial texture of the MgO is well transferred to the DyBCO. A growth model for the DyBCO is presented. [Copyright &y& Elsevier]

DyBa2Cu3O7-x (DyBCO) films with MgO buffer layers were grown on Hastelloy substrates by inclined substrate deposition (ISD). An almost linear increase of the critical current with the DyBCO film thickness was observed. A maximum critical current of 1018 A cm-1 was measured for a DyBCO film with 5.9 μm thickness, yielding a critical current density of 1.7 MA cm-2 at 77 K and self-field. Transmission electron microscopy (TEM) yielded highly biaxially textured DyBCO films at all thicknesses and, thus, no significant decrease of the critical current density occurs with the film thickness. ISD yields a non-zero component of the growth direction parallel to the DyBCO (a, b)-plane since the DyBCO grows on a faceted MgO surface and avoids a-axis growth. Therefore, the ISD technology offers a unique possibility to overcome thickness limitations in coated conductor technology. [ABSTRACT FROM AUTHOR]

DyBa2Cu3O7-x (DyBCO) films with MgO buffer layers were grown on Hastelloy substrates by inclined substrate deposition (ISD). An almost linear increase of the critical current with the DyBCO film thickness was observed. A maximum critical current of 1018 A cm-1 was measured for a DyBCO film with 5.9 μm thickness, yielding a critical current density of 1.7 MA cm-2 at 77 K and self-field. Transmission electron microscopy (TEM) yielded highly biaxially textured DyBCO films at all thicknesses and, thus, no significant decrease of the critical current density occurs with the film thickness. ISD yields a non-zero component of the growth direction parallel to the DyBCO (a, b)-plane since the DyBCO grows on a faceted MgO surface and avoids a-axis growth. Therefore, the ISD technology offers a unique possibility to overcome thickness limitations in coated conductor technology. [ABSTRACT FROM AUTHOR]

The research field of thermoelectricity was renewed by the progress made in nanostructuring approaches and by the investigation of new material groups as skutterudites, whose most promising representative is CoSb 3 . In this work Co–Sb thin films with a thickness of 30 nm were deposited by molecular beam deposition at different substrate temperatures as well as on non-heated substrates followed by a post-annealing step. An extended investigation of the phase formation in dependence of deposition method and parameters, film composition, and post-treatment is given. The presented results provide different routes to achieve high quality single phase films. It was also demonstrated that the grain size of the CoSb 3 thin films is very sensitive to the used deposition method and especially on the substrate temperature during deposition. A controllable grain size by changing the deposition parameters could be a key feature for the optimization of the thermoelectric properties, since especially the thermal conductivity should strongly depend on the grain size due to enhanced grain boundary scattering of phonons. [ABSTRACT FROM AUTHOR]

Abstract: Sb2Te3 and Bi2Te3 thin films were grown at room temperature on SiO2 and BaF2 substrates using molecular beam epitaxy. A layer-by-layer growth was achieved such that metallic layers of the elements with 0.2nm thickness were deposited. The layer structure in the as-deposited films was confirmed by X-ray diffraction and was seen more clearly in Sb2Te3 thin films. Subsequent annealing was done at 250°C for 2h and produced the Sb2Te3 and Bi2Te3 crystal structure as confirmed by high-energy X-ray diffraction. This preparation process is referred to as nano-alloying and it was demonstrated to yield single-phase thin films of these compounds. In the thin films a significant texture could be identified with the crystal c axis being almost parallel to the growth direction for Sb2Te3 and tilted by about 30° for Bi2Te3 thin films. In-plane transport properties were measured for the annealed films at room temperature. Both films yielded a charge carrier density of about 2.6×1019 cm−3. The Sb2Te3 films were p-type, had a thermopower of +130μVK−1, and surprisingly high mobilities of 402cm2 V−1 s−1. The Bi2Te3 films were n-type, showed a thermopower of −153μVK−1, and yielded significantly smaller mobilities of 80cm2 V−1 s−1. The chemical composition and microstructure of the films were investigated by transmission electron microscopy (TEM) on cross sections of the thin films. The grain sizes were about 500nm for the Sb2Te3 and 250nm for the Bi2Te3 films. In the Bi2Te3 thin film, energy-filtered TEM allowed to image a Bi-rich grain boundary phase, several nanometers thick. This secondary phase explains the poor mobilities of the Bi2Te3 thin film. With these results the high potential of the nano-alloying deposition technique for growing films with a more complex layer architecture is demonstrated. [Copyright &y& Elsevier]