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Register a new userElectronic properties of A2Zr2O7 (A= Gd, Nd) ceramic
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Added by
Ajay Himanshu Himanshu
Publication date
2019
fields
Physics
and research's language is
English
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The density functional theory with generalized gradient approximation has been used to investigate the electronic structure of gadolinium pyrochlore A2Zr2O7 (A=Gd, Nd) ceramic synthesized in polycrystalline form by solid state reaction. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Rietveld analysis of the XRD pattern. The Zr-K edge X-ray absorption (XAFS) spectra of A2Zr2O7 (A=Gd, Nd) were analysed together with those Zr-foil, which was used as reference compounds. X-ray photoemission spectroscopy (XPS), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) for A2Zr2O7 (A=Gd, Nd) has been employed to obtain quantitative structural information on the Zr-local environment. The band gap is estimated using UV-Vis spectroscopy. The crystal structure is face centered cubic, space group being Fd-3m (No. 227). The total energies in this work were calculated using the generalized gradient approximation to DFT plus on-site repulsion (U) method.
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Rare-earth (RE) based frustrated magnets as typical systems of combining strong spin-orbit coupling, geometric frustration and anisotropic exchange interactions, can give rise to diverse exotic magnetic ground states such as quantum spin liquid (QSL). The discovery of new RE-based frustrated materials is crucial for exploring the exotic magnetic phases. Herein, we report the synthesis, structure and magnetic properties of a family of melilite-type RE2Be2GeO7 (RE = Pr, Nd, Gd-Yb) compounds crystallized in a tetragonal structure, where magnetic RE3+ ions lay out on Shastry-Sutherland lattice (SSL) within ab-plane and are well separated by nonmagnetic GeBe2O7 polyhedrons along c-axis. Temperature-dependent susceptibilities and isothermal magnetization M(H) measurements reveal that most RE2Be2GeO7 compounds except RE=Tb show no magnetic ordering down to 2 K despite the dominant antiferromagnetic (AFM) interactions, where Tb2Be2GeO7 undergoes AFM transition with Neel temperature TN~ 2.5 K and field-induced spin flop behaviors (T< TN). In addition, the calculated magnetic entropy change from the isothermal M(H) curves reveal a viable magnetocaloric effect (MCE) for RE2Be2GeO7 (RE =Gd, Dy) in liquid helium temperature regimes, Gd2Be2GeO7 shows maximum Sm up to 54.8 J K-1 Kg-1 at H= 7 T and Dy2Be2GeO7 has largest value Sm=16.1 J K-1 kg-1 at H= 2 T in this family. More excitingly, rich diversity of RE ions in this family enables an archetype for exploring exotic quantum magnetic phenomena with large variability of spin located on SSL lattice.
We present a detailed study of the magnetic-field and temperature-dependent polarization of the near-band-gap photoluminescence in Gd-doped GaN layers. Our study reveals an extraordinarily strong influence of Gd doping on the electronic states in the GaN matrix. We observe that the spin splitting of the valence band reverses its sign for Gd concentrations as low as 1.6 x 10^{16} cm^{-3}. This remarkable result can be understood only in terms of a long range induction of magnetic moments in the surrounding GaN matrix by the Gd ions.
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