Temperature dependent structural properties of Mn1.90M0.10O3(M = Cr and Fe).

The polycrystalline samples of Mn1.90Cr0.10O3(MCO) and Mn1.90Fe0.10O3(MFO) have been investigated for their temperature dependent magnetic and structural properties. The Cr and Fe substitutions have significant effect on the magnetic and structural properties of Mn2O3. Like pristine Mn2O3, the Cr and Fe substituted samples MCO and MFO also exhibit two antiferromagnetic transitions; one at ∼77 K, ∼80 K, respectively and another at ∼40 K. Our room temperature synchrotron x-ray powder diffraction (SXRD) results confirm that both the MCO and MFO samples crystallize in cubic symmetry. The temperature dependent SXRD results demonstrate the cubic to orthorhombic structural transition for the studied samples. The pristine Mn2O3shows cubic to orthorhombic transition around 310 K, whereas this structural transition shifted towards lower temperature side with these substitutions i.e. around 240 K for MCO and 260 K for MFO. Interestingly, the centrosymmetricPcabto non-centrosymmetricPca21change in symmetry is also resolved at the ferroelectric ordering temperature for MCO.

Electronic correlations in epitaxial CrN thin film.

Chromium nitride (CrN) spurred enormous interest due to its coupled magnetostructural and unique metal-insulator transition. The underneath electronic structure of CrN remains elusive. Herein, the electronic structure of epitaxial CrN thin film has been explored by employing resonant photoemission spectroscopy (RPES) and X-ray absorption near edge spectroscopy study in combination with the first-principles calculations. The RPES study indicates the presence of a charge-transfer screened 3[Formula: see text] ([Formula: see text]: hole in the N-2[Formula: see text]) and 3[Formula: see text] final-states in the valence band regime. The combined experimental electronic structure along with the orbital resolved electronic density of states from the first-principles calculations reveals the presence of Cr(3[Formula: see text])-N(2[Formula: see text]) hybridized (3[Formula: see text]) states between lower Hubbard (3[Formula: see text]) and upper Hubbard (3[Formula: see text]) bands with onsite Coulomb repulsion energy (U) and charge-transfer energy ([Formula: see text]) estimated as [Formula: see text] 4.5 and 3.6 eV, respectively. It verifies the participation of ligand (N-2[Formula: see text]) states in low energy charge fluctuations and provides concrete evidence for the charge-transfer ([Formula: see text]U) insulating nature of CrN thin film.

Effect of disorder on superconductivity of NbN thin films studied using x-ray absorption spectroscopy.

The superconducting transition temperature (TC) of rock-salt type niobium nitride (δ- NbN) typically varies between 9 to 17 K and the theoretically predicted value of 18 K has not been achieved hitherto. The lowTCinδ- NbN has been assigned to some structural disorder which is always present irrespective of the microstructure (polycrystalline or epitaxial), methods or conditions adopted during the growth of NbN thin films. In this work, we investigate the atomic origin of such suppression of theTCinδ- NbN thin films by employing combined methods of experiments andab initiosimulations. Sputteredδ- NbN thin films with different disorder were studied using the synchrotron-based N and Nb K-edge x-ray absorption spectroscopy techniques. A strong correlation between the superconductivity and the electronic structure reconstruction was observed. The theoretical analysis revealed that under N-rich growth conditions, atomic and molecular N-interstitial defects assisted by cation vacancies form spontaneously and results into a smeared electronic structure around Fermi-level. The role of electronic smearing on theTCis thoroughly discussed.

Real-space imaging of magnetic phase transformation in single crystalline Sm-Ca-Sr based manganite compound.

Low-temperature-high-magnetic field magnetic force microscopy studies on colossal magnetoresistance material Sm0.5Ca0.25Sr0.25MnO3have been carried out. These measurements provide real-space visualization of antiferromagnetic-ferromagnetic (AFM-FM) transition on sub-micron length scale and explain the presence of AFM-FM transition in the temperature-dependent magnetization measurements, but the absence of corresponding metal-insulator transition in temperature-dependent resistivity measurements at the low magnetic field. Distribution of transition temperature over the scanned area indicates towards the quench disorder broadening of the first-order magnetic phase transition. It shows that the length scale of chemical inhomogeneity extends over several micrometers.

Enhancement of magnetoelectric coupling in Cr doped Mn2O3.

The effect of Cr doping has been undertaken to investigate its effect on the structural, magnetic, dielectric and magnetoelectric properties of newly discovered multiferroics material α-Mn2O3. The Cr doping modifies the room temperature crystal symmetry i.e. transforms from orthorhombic to cubic symmetry. Similar to α-Mn2O3, two magnetic transitions have been observed in all Cr doped samples. The effect of Cr doping manifested on the low temperature transition. The lower magnetic transition shifted toward higher temperature (25 K for pristine to 40 K for Cr = 10%) whereas the high temperature transition decreases slightly with increasing Cr content. A clear frequency independent transition is observed in temperature dependent complex dielectric measurements for Mn2-x Cr x O3 (0 ⩽ x ⩽ 0.10) samples around high temperature magnetic ordering ∼80 K which corroborate the magnetoelectric coupling in these samples. Interestingly, the magnetodielectric value enhanced significantly with Cr doping and a maximum increase of ∼21% is observed for 10% Cr doped sample at 5 K around 70 kOe magnetic field.

Origin of step-like behavior in the Co/Si system.

A systematic investigation of the structure, nature of the interface and their possible connections with magnetic properties for the as-deposited Co/Si/Co trilayer system has been carried out. X-ray reflectivity, cross-sectional transmission electron microscopy and x-ray emission measurements performed on the Co/Si/Co trilayer system show that when the Si layer thickness is less than ∼ 20 Å, the full Si layer is converted into a cobalt silicide layer whereas when the Si layer thickness > 20 Å along with the silicide layer. the pure Si layer also remains. A comparison of magneto-optical Kerr effect and magnetoresistance measurements reveals the absence of antiferromagnetic coupling in these samples. Double-step-like magnetization, in the case of Si layer thickness > 20 Å between two Co layers, is explained by magnetization reversal of two ferromagnetic layers having different coercivities, independent of each other.