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Scientific reports 11(1), 524 (1-14) (2021). doi:10.1038/s41598-020-79895-7, Band structure tailoring has been a great avenue to achieve the half-metallic electronic ground state in materials. Applying this approach to the full Heusler alloy Fe$_2$TiSn, Cr is introduced systematically at Ti site that conforms to the chemical formula Fe$_2$Ti$_{1−x}$Cr$_x$Sn. Compositions so obtained have been investigated for its electronic, magnetic, and electrical transport properties with an aim to observe the half-metallic ferromagnetic ground state, anticipated theoretically for Fe$_2$CrSn. Our experimental study using synchrotron X-ray diffraction reveals that only compositions with $x$≤ 0.25 yield phase pure L2$_1$ cubic structures. The non-magnetic ground state of Fe$_2$TiSn gets dramatically affected upon inclusion of Cr giving rise to a localized magnetic moment in the background of Ruderman–Kittel–Kasuya–Yosida (RKKY) correlations. The ferromagnetic interactions begin to dominate for x = 0.25 composition. Results of its resistivity and magnetoresistance (MR) measurement point towards a half-metallic ground state. The calculation of exchange coupling parameter, J$_{ij}$, and orbital projected density of states that indicate a change in hybridization between 3d and 5p orbital, support the observations made from the study of local crystal structure made using the extended X-ray absorption fine structure spectroscopy. Our findings here highlight an interesting prospect of finding half-metallicity via band structure tailoring for wide application in spintronics devices., Published by Macmillan Publishers Limited, part of Springer Nature, [London]

The present paper seeks to investigate effect of Mn doping in superconducting FeSe. It is found that over the entire doping range in Fe$_{1-x}$Mn$_x$Se ($0 \le x \le 1$), Mn does not substitute Fe in the superconducting tetragonal phase. Instead two impurity phases, NiAs type hexagonal phase and NaCl type cubic phase grow with increasing Mn content. Initially, hexagonal phase has a higher content than the cubic phase but beyond $x$ = 0.5, the cubic phase grows rapidly and for $x \ge 0.8$, the sample is monophasic with cubic NaCl type structure. The superconducting tetragonal phase content steadily decreases with increasing Mn concentration and completely disappears beyond $x = 0.5$. The premise that Mn never replaces Fe in the superconducting phase is further strengthened by observation of a sharp drop in AC susceptibility akin to superconducting transition at the T$_c$ of FeSe up to $x$ = 0.5. EXAFS studies at the Fe K edge also show that the Fe has a four coordinated tetragonal local structure in all compositions below $x = 0.5$, similar to that in FeSe and it gradually changes to a six coordinated one as is expected for a NaCl type cubic phase for $x \ge 0.5$.

Combination of high optical transparency and good electrical conductivity is realized in CuCrO$_2$, a $p$-type transparent conducting oxide. With an aim to better its physical properties, CuCr$_{1-x}$Ti$_{x}$O$_{2}$ ($x$ = 0, 0.05, 0.1) series was prepared and investigated for its structural, electrical transport and optical properties. Along with lattice parameter values, refinement of X-ray diffraction profiles confirms the solubility limit of Ti within the delafossite unit cell. Electrical resistivity and heat capacity measured by varying the temperature, further characterize the Ti-substituted compositions. As determined from the ultraviolet-visible (UV-Vis) spectroscopy, no significant change takes place in the optical gap of CuCrO$_2$ with Ti addition. Apart from confirming the $4+$ valence state of Ti, X-ray absorption near edge structure highlight the subtle changes taking place in the Cu$-$O hybridization upon Ti - substitution. Analysis of temperature dependent extended X-ray absorption fine structure (EXAFS) spectroscopy recorded at the Cr and Cu K-edge emphasizes the impact of redistribution of charges on the local crystal structure. Cu$-$Cu hybridization along $a$-axis appears to be influenced mainly by the temperature and only slightly by Ti substitution.

Journal of applied physics 122(22), 225111 (2017). doi:10.1063/1.5003965, Combination of high optical transparency and good electrical conductivity is realized in CuCrO$_2$, a $p$-type transparent conducting oxide. With an aim to better its physical properties, CuCr$_{1-x}$Ti$_{x}$O$_{2}$ ($x$ = 0, 0.05, 0.1) series was prepared and investigated for its structural, electrical transport and optical properties. Along with lattice parameter values, refinement of X-ray diffraction profiles confirms the solubility limit of Ti within the delafossite unit cell. Electrical resistivity and heat capacity measured by varying the temperature, further characterize the Ti-substituted compositions. As determined from the ultraviolet-visible (UV-Vis) spectroscopy, no significant change takes place in the optical gap of CuCrO$_2$ with Ti addition. Apart from confirming the $4+$ valence state of Ti, X-ray absorption near edge structure highlight the subtle changes taking place in the Cu$-$O hybridization upon Ti - substitution. Analysis of temperature dependent extended X-ray absorption fine structure (EXAFS) spectroscopy recorded at the Cr and Cu K-edge emphasizes the impact of redistribution of charges on the local crystal structure. Cu$-$Cu hybridization along $a$-axis appears to be influenced mainly by the temperature and only slightly by Ti substitution., Published by American Inst. of Physics, Melville, NY

Magnetism in Ni-Mn-Z (Z = Ga,In,Sn,Sb) Heusler alloys has so far been predominantly attributed to Rudermann-Kittel-Kasuya-Yoshida type interactions between Mn atoms. We investigate magnetic interactions in one such alloy, Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ and attempt to explain the origin of antiferromagnetic (AFM) interactions that coexist with ferromagnetic ones. Through the combination of x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD), we find that Ni plays an important role along with Mn in the overall magnetism. A significant hybridization that develops between Mn and Ni orbitals results in a small antiferromagnetic moment at Ni sites. The shift in the XMCD hysteresis loops in the martensitic phase suggests that antiferromagnetism results from superexchange like interactions between Mn atoms mediated by Ni., Comment: Main paper 6 pages + supplementary material

Extended x-ray absorption fine-structure (EXAFS) measurements have been carried out on Ni$_{50}$Mn$_{35}$Sn$_{15}$ in the austenitic and martensitic phase. The temperatures associated with structural and magnetic phase transformations are obtained from magnetization measurements. The system orders ferromagnetically below 319 K while the structural phase transition occurs at T$_M$ $\sim$ 200 K. EXAFS measurements have been carried out at Mn and Ni K-edges and changes associated with respect to the local structure of these absorbing atoms are compared. Significant changes in the nearest neighbour interactions are seen as the system transits to the low temperature martensitic phase. EXAFS provides evidence for local structural distortion even in the cubic phase that is not seen from the x-ray diffraction studies. The results obtained are understood in terms of changing hybridization between the constituent atoms that influence the electronic structure at the Fermi level, associated with the austenitic-to-martensitic transition., 20 pages, 9 figures

The local atomic structure of Ni$_{2+x}$Mn$_{1-x}$Ga with 0 $\le$ $x$ $\le$ 0.16 alloys was explored using Mn and Ga K-edge Extended X-ray Absorption Fine Structure (EXAFS) measurement. Inorder to study the atomic re-arrangements that occur upon martensitic transformation, room temperature and low temperature EXAFS were recorded. The changes occurring in the L2$_1$ unit cell and the bond lengths obtained from the analysis enables us to determine the modulation amplitudes over which the constituent atoms move giving rise to shuffling of the atomic planes in the modulated structure. The EXAFS analysis also suggests the changes in hybridization of Ga-$p$ and Ni-$d$ orbitals associated with the local symmetry breaking upon undergoing martensitic transition., Accepted for publication in Physical Review B

The local atomic structure of Ni-Mn-Ga alloys was explored using Mn and Ga K-edge extended X-ray fine structure (EXAFS) measurement. The changes occuring in the L1$_0$ sub-cell of the martensitic unit cell and the bond lengths obtained from the analysis enables us to propose a scheme for the structural distortions responsible for the modulations and shuffling of the atomic planes in the martensitic phase of Ni-Mn-Ga system. The EXAFS analysis also suggests the changes in hybridization of Ga-$p$ and Ni-$d$ orbitals associated with the local symmetry breaking upon undergoing martensitic transition., Comment: 9 pages, 4 figures