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Abstract: Random variation of band bowing in pulsed laser deposited Mg doped (x=0.090, 0.147, 0.211, 0.268) ZnO thin films was observed. The X-ray diffraction and ultraviolet–visible spectroscopy data reveal lattice relaxation and increase in band gap as well as disorderness in the samples. The X-ray photoelectron spectroscopy data confirm the presence of magnesium and oxygen interstitials (Mg i and O i ) as well as oxygen vacancies (V O ). The randomness of band bowing is attributed to the presence of these defects. [Copyright &y& Elsevier]

Graphical abstract The histogram shows that the values of change in entropy (ΔS max), relative cooling power (RCP), and Curie temperature (T c) for current samples (La 0.90 Zr 0.10 MnO 3) are simultaneously enhanced and are comparable with the family of La-manganite materials and standard gadolinium (Gd) bulk sample. The dotted orange line shows the room temperature. The inset shows the table with serial number and the corresponding materials with their respective references. (Note: ΔS max and RCP values are taken at ΔH = 5T). Highlights • La 1−x Zr x MnO 3 (x = 0.05, 0.10 and 0.15) samples synthesized by chemical combustion. • Magnetic transition near-room-temperature with the second-order phase transition. • Short-range exchange interactions help in enhanced magnetic and magnetocaloric values. • Change in entropy |ΔS m | at 5 T is 4.04 J·kg−1·K−1 at 304 K for La 0.90 Zr 0.10 MnO 3 sample. • Potential material for future magnetic refrigeration works at near room-temperature. Abstract Near-room-temperature and enhanced magnetocaloric properties are investigated for the chemical combustion synthesized electron-doped manganite La 1−x Zr x MnO 3 with x = 0.05, 0.10 and 0.15. The single-phase rhombohedral crystal structure is observed particularly for the La 0.90 Zr 0.10 MnO 3 (Zr10) system. Importantly, all the samples exhibit the paramagnetic-to-ferromagnetic (PM-to-FM) transition close to the room-temperature with the second-order phase transition. The analysis of the magnetic data in the critical region with different theoretical models such as 3D-Heisenberg, 3D-Ising, Mean-field, and Tri-critical mean-field suggested that the Zr10 sample exhibits the typical 3D-Heisenberg ferromagnetic characteristics. This indicated that the enhanced magnetic and magnetocaloric properties are governed by short-range exchange forces. Furthermore, the obtained data is also fitted with the Kouvel-Fisher method to obtain the transition-temperature, critical exponent β and it is found that the transition temperature and β values are totally consistent to that of the 3D-Heisenberg model. Significantly, the change in entropy |ΔS m | at 5 T is calculated to be 4.04 J·kg−1·K−1 at 304 K in case of Zr10 sample indicating that it can be one of the potential material for the future magnetic refrigeration technology working at near room-temperature. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the gamma irradiation effects on the structural and optical properties of N-doped 4H-SiC (n-4H-SiC) is presented up to a cumulative gamma radiation dose of 1500 kGy. The studies showed marginal and inconsistent variation in the c - and a -axis lattice constants of 4H-SiC due to the accumulation of gamma-induced defect states. The modifications in the longitudinal optical plasmon-phonon coupled (LOPC) modes, Biedermann absorption bands, Urbach energy (E U) and defect related photoluminescence (DPL) bands are discussed at different (500, 1000 and 1500 kGy) irradiation doses. Despite these effects, the overall gamma-induced disorder (1 - A n o r m) and variation in the free carrier concentrations (n) are found to be negligible and demonstrating the radiation resistant property of n-4H-SiC under gamma radiation environment. [ABSTRACT FROM AUTHOR]

Abstract Magneto-electric and electronic properties of Nd 1- x Sr x MnO 3-δ (0.3 ≤ x ≤ 0.7) (NSMO) nanoparticles are investigated. NSMO nanoparticles are synthesized by glycine assisted auto combustion method. The structural and morphological properties are probed using X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). NSMO crystallizes in orthorhombic structure and nearly spherical agglomerated morphology is observed. Resistivity of the order of few MOhm-cm is recorded for all the compositions and the transport mechanism is interpreted by using Mott variable range hopping (VRH) model. In absence of magnetic field all samples show insulating nature over the studied temperature region (300- 5 K), while Metal to Insulator transition is observed in the presence of magnetic field (8T). Large Colossal Magnetoresistance (CMR) is noticed below 50 K for NSMO. Observed Curie temperature is in the range of 102–115 K and it is found to be independent of Strontium doping concentration. Bifurcation in FC-ZFC, for all the samples, is at higher temperature than blocking temperature (∼72 K) indicates glassy state. We have calculated thickness of magnetic dead layer by two different ways and it lies between 1.6 and 2.9 nm. Concentration of divalent element and oxygen non-stoichiometry affects the relative fraction of Mn3+/Mn4+ ions. Mn3+/Mn4+ in our samples is determined from areas under the deconvoluted X-Ray Photoelectron Spectra (XPS) of Mn core level. The Mn3+/Mn4+ ratio is higher than the value expected from nominal composition, which indicates oxygen non-stoichiometry. Oxygen non-stoichiometry is also confirmed by chemical titration method. Highlights • Synthesis of NSMO nanoparticles by glycine assisted auto combustion method is presented. • Effect of particle size and surface stress on unit cell volume is examined. • VRH mechanism, Abeles model, oxygen deficiency and core shell model are used to explain transport properties. • Magnetic properties of NSMO nanoparticles are discussed by considering magnetic dead layer. • Oxygen non-stoichiometry is probed by XPS and Iodometric titration. [ABSTRACT FROM AUTHOR]

Highlights • Under-doped to over-doped boron doped diamond films. • T c suppression in boron doped diamond films. • Impurity band structure across the metal-to-insulator (MIT) transition. • Core excitons in superconducting boron doped diamond films. Abstract Our work investigates the impurity band and the core excitonic level evolution of a series of systematically boron doped diamond (BDD) films using Raman and X-ray absorption (XAS) spectroscopies. The resistivity versus temperature data shows that T c of the BDD films achieves a peak at a maximum gaseous phase boron to carbon ratio, [ B C ] max , beyond which T c drops gradually as a result of excess defect formation, revealing a dome-shaped behaviour. Study of lattice expansion clearly shows the unambiguous presence of substitutional boron atoms beyond [ B C ] max. Direct probe of the impurity band using XAS show a systematic increase in the absorption intensity of the bandgap states which ultimately degrades as the limit of B C > [ B C ] max is exceeded. The binding energy of the BDD 1s core exciton reveal a shallow measured value of 0.11 eV. This is less than earlier found values of 0.19 - 1.2 eV, in various reports for intrinsic diamond. [ABSTRACT FROM AUTHOR]

Radio Frequency magnetron sputtering technique has been used to prepare Ni doped ZnO thin films with varying Ni doping concentration of upto 10 at.%. Grazing Incidence X-ray Diffraction results show wurtzite structure of the samples throughout the Ni concentration range while X-ray Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure results at Zn and Ni K edges show that Ni is substituting Zn in ZnO lattice and no other extra phase is present in the samples. The substitution of Zn by Ni is further confirmed by O K-edge XANES measurements. Photoluminescence measurements on the samples and theoretical simulations of the XANES spectra at Ni and O K-edges have been used to explain the room temperature ferromagnetic character on the basis of the presence of oxygen vacancies in the samples. [ABSTRACT FROM AUTHOR]

Hole-doped La 2 CoO 4 compounds have been widely studied due to their multifaceted behavior such as charge ordering, spin ordering and spin blockade. Hole doping in La 2 CoO 4 causes appearance of the Co 3+ along with the Co 2+ , which makes it an interesting model system for study of the spin-state transitions. In hole-doped samples, the spin-states of the Co 3+ ions at large have been reported as the low or intermediate state. We report here a study on the Sr doping in La 2 CoO 4 . The Sr doping has been found to stabilize the crystal structure. By combining structural, electronic structure and electrical transport results, it is observed that the high-spin state is present in all the La 2− x Sr x CoO 4 (x = 0.5, 0.8, 0.9 and 1.0) samples. The high-spin state has been found to be concomitant with the delocalization of the e g electrons. In addition, in these materials, a colossal thermopower has been observed for first time in the cryogenic temperatures. [ABSTRACT FROM AUTHOR]

The structural, magnetic and magneto-transport of undoped ZnO, Zn 0.97 Al 0.03 O, Zn 0.95 Fe 0.05 O and Zn 0.92 Al 0.03 Fe 0.05 O thin films grown on Si(100) substrate using pulsed laser deposition were investigated. The single phase nature of the films is confirmed by X-ray diffraction and Raman spectroscopy measurements. The possibility of Fe metal cluster in Fe doped/co-doped films is ruled out by Fe 2p core level photoelectron spectra. From O 1s core level spectra it is observed that oxygen vacancy is present in all the films. The undoped ZnO film shows magnetic ordering below ∼175 K, whereas Fe doped/codoped samples show magnetic ordering even at 300 K. The Al doped sample reveals paramagnetic behavior. The magneto-transport measurements suggest that the mobile carriers undergo exchange interaction with local magnetic moments. [ABSTRACT FROM AUTHOR]

Relationship between magnetism and structure of Cu-doped ZnO was investigated at macroscopic and microscopic levels. Thin Zn 1−x Cu x O films ( x = 0.02, 0.04, 0.07 and 0.10) were prepared by a pulsed laser deposition and characterized via superconducting quantum interference device (SQUID) magnetometry, high-resolution x-ray diffraction, and Cu K -edge and Zn K -edge x-ray absorption, x-ray linear dichroism and x-ray circular magnetic dichroism spectroscopy. Even though the samples exhibit room-temperature ferromagnetism with magnetization that increases with Cu concentration, we did not detect signatures of local magnetic moments associated with Cu atoms, as evidenced by the lack of any XMCD signal. The host ZnO wurtzite lattice is not significantly altered by the addition of Cu. At the same time, most of the Cu atoms are not incorporated into the wurtzite lattice but rather have a CuO-like coordination. These results indicate that ferromagnetism of the investigated Zn 1−x Cu x O films is not directly linked to the doping atoms but rather is due to some other changes which have been introduced to the host ZnO by the dopants. [ABSTRACT FROM AUTHOR]

Fe (4 at.%) doped europium (III) oxide thin film was deposited on silicon (1 0 0) substrate by pulsed laser deposition technique. Structural, spectral and magnetic properties were studied by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and magnetization measurements. XRD and Raman spectroscopy reveal that the grown film is single phased and belongs to the cubic structure of Eu 2 O 3 . XPS study of the Eu 1.92 Fe 0.08 O 3 film shows that Fe exists in Fe 3+ ionic state in the film. The film exhibits magnetic ordering at room temperature. [ABSTRACT FROM AUTHOR]

• Fe-doped TiO 2 amorphous thin films deposited using rf magnetron sputtering. • Band-gap energy reduction with Fe doping due to oxygen vacancy. • Maximum Fe substitution is up to 2 at. % doping. The present study deals with the local structure of amorphous TiO 2 and Fe-doped TiO 2 thin films deposited on Si substrate using magnetron sputtering. The absence of long range order is confirmed by grazing incidence x-ray diffraction and the short range order is studied using x-ray absorption near edge structure (XANES) measurements at Ti, Fe and O K-edges and Fe and Ti L 3 -edge. The XANES provides understanding about the electronic transition induced from the short range ordering and dependence of electronic hybridization of the central Ti- p orbitals with the Ti- d orbitals. The XANES measurements also show that maximum Fe doping concentration allowed to replace Ti is 2 at.% and after that separate phase starts appearing, which is consistent with simulation by ab-initio multiple scattering theory based code FEFF9. Ellipsometry measurements show gradual decrease in band-gap energy upto 2 at.% Fe doping from pristine TiO 2 , however a drastic decrease in band-gap energy is observed at 4 at.% or higher doping concentration due to formation of other phases. [ABSTRACT FROM AUTHOR]