(2015) Structural and magnetic investigations of single-crystalline neodymium zirconate pyrochlore Nd2Zr2O7. Physical Review B (Condensed Matter and Materials Physics), 91 (17). 174416. Permanent WRAP URL:http://wrap.warwick.ac.uk/87756 Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes this work by researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-for-profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. We report structural and magnetic properties studies of large high-quality single crystals of the frustrated magnet Nd 2 Zr 2 O 7 . Powder x-ray diffraction analysis confirms that Nd 2 Zr 2 O 7 adopts the pyrochlore structure. Room-temperature x-ray diffraction and time-of-flight neutron-scattering experiments show that the crystals are stoichiometric in composition with no measurable site disorder. The temperature dependence of the magnetic susceptibility shows no magnetic ordering at temperatures down to 0.5 K. Fits to the magnetic susceptibility data using a Curie-Weiss law reveal a ferromagnetic coupling between the Nd moments. Magnetization versus field measurements show a local Ising anisotropy along the 111 axes of the Nd 3+ ions in the ground state. Specific heat versus temperature measurements in zero applied magnetic field indicate the presence of a thermal anomaly below T ∼ 7 K, but no evidence of magnetic ordering is observed down to 0.5 K. The experimental temperature dependence of the single-crystal bulk dc susceptibility and isothermal magnetization are analyzed using crystal field theory and the crystal field parameters and exchange coupling constants determined. Publisher

Abstract. Magnetic and magnetoelastic properties of terbium titanate pyrochlore in paramagnetic phase are simulated. The magnetic field and temperature dependences of magnetization and forced magnetostriction in Tb 2 Ti 2 O 7 single crystals and polycrystalline samples are calculated in the framework of exchange charge model of crystal field theory and a mean field approximation. The set of electron-deformation coupling constants has been determined. Variations of elastic constants with temperature and applied magnetic field are discussed. Additional strong softening of the crystal lattice at liquid helium temperatures in the magnetic field directed along the rhombic symmetry axis is predicted.

Abstract-In terms of a semi-phenomenological exchange charge model, we have obtained estimates of parameters of the crystal field and parameters of the electron-deformation interaction in terbium titanate Tb 2 Ti 2 O 7 with a pyrochlore structure. The obtained set of parameters has been refined based on the analysis of spectra of neutron inelastic scattering and Raman light scattering, field dependences of the forced magnetostriction, and temperature dependences of elastic constants. INTRODUCTIONInterest in investigations of rare-earth (RE) crystals with a pyrochlore structure (rare-earth ions form a three-dimensional network of tetrahedra with connected vertices) is mainly determined by the wide diversity of magnetic behavior that they exhibit at low temperatures [1]. Among titanates RE 2 Ti 2 O 7 , of most interest is terbium titanate Tb 2 Ti 2 O 7 , in which the magnetic long-range order does not manifest itself at least to a temperature of 15 mK [2], whereas, in accordance with calculations, the phase transition from the paramagnetic to an antiferromagnetic state should have occurred at a temperature of 1.8 K [3]. Interestingly, an external pressure induces a long-range magnetic order in Tb 2 Ti 2 O 7 : under a pressure of 8.6 GPa at temperatures below 2.1 K, apart from the spin-liquid phase, an antiferromagnetic order with a complex magnetic structure is observed [4,5].It is known that magnetoelastic interactions can strongly affect the magnetic behavior of rare-earth compounds. In terbium titanate single crystals and powders, an anomalously large parastriction (deformation of the lattice in the paramagnetic phase in an external magnetic field) has been revealed, which achieves values of ~10 -4 in magnetic fields ~1 T at liquid-helium temperatures [6][7][8]. The parastriction of isostructural crystals Dy 2 Ti 2 O 7 and Ho 2 Ti 2 O 7 under the same conditions acquires values that are typical for paramagnets (~10 -6 ) [9]. In addition, in Tb 2 Ti 2 O 7 , an anomalous decrease in the Young modulus and elastic constants upon lowering temperature was revealed [10][11][12][13]. The cooperative Jahn-Teller effect (spontaneous symmetry violation caused by interactions of rare-earth ions via fields of static and dynamic deformations) can suppress the magnetic ordering. In [10], the temperature of a possible structural phase transition was estimated to be c T  0.1 K. Previously, using a semi-phenomenological model of the crystal field, we have calculated parameters that characterize changes in the crystal field caused by macroscopic deformations of the lattice [14]. The change in the elasticity modulus C 44 of Tb 2 Ti 2 O 7 crystals in the temperature range of 100-4.2 K calculated with this set of parameters is consistent with measurement data. However, the change in elasticity modulus 11

The ground state band structure, magnetic moments, charges and population numbers of electronic shells of Cu and Fe atoms have been calculated for chalcopyrite CuFeS 2 using density functional theory. The comparison between our calculation results and experimental data (X-ray photoemission, X-ray absorption and neutron diffraction spectroscopy) has been made. Our calculations predict a formal oxidation state for chalcopyrite as Cu 1+ Fe 3+ S 2 2-. However, the assignment of formal valence state to transition metal atoms appears to be oversimplified. It is anticipated that the valence state can be confirmed experimentally by nuclear magnetic and nuclear quadrupole resonance and Mössbauer spectroscopy methods.

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