The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform
James S Speck - One of the best experts on this subject based on the ideXlab platform.
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impact of thermal strain on the dielectric constant of sputtered barium strontium titanate thin films
Applied Physics Letters, 2002Co-Authors: T R Taylor, P J Hansen, B Acikel, Nadia K Pervez, R A York, S K Streiffer, James S SpeckAbstract:Barium strontium titanate thin films were deposited by sputtering on Pt/SiO2 structures using five different host substrates: magnesium oxide, strontium titanate, sapphire, silicon, and vycor glass. These substrates were chosen to provide a systematic change in thermal strain while maintaining the same film microstructure. All films have a weakly textured microstructure. Temperature dependent dielectric measurements from 100–500 K determined that decreasing thermal expansion coefficient of the host substrate (i.e., larger tensile thermal strain) reduced the film dielectric permittivity. The experimentally determined Curie–Weiss Temperature decreased with increasing tensile thermal strain and the Curie–Weiss constant increased with tensile strain as predicted by Pertsev et al. [J. Appl. Phys. 85, 1698 (1999)].
Michel J P Gingras - One of the best experts on this subject based on the ideXlab platform.
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dynamically induced frustration as a route to a quantum spin ice state in tb2ti2o7 via virtual crystal field excitations and quantum many body effects
Physical Review Letters, 2007Co-Authors: Hamid R Molavian, Michel J P Gingras, Benjamin CanalsAbstract:: The Tb2Ti2O7 pyrochlore magnetic material is attracting much attention for its spin liquid state, failing to develop long-range order down to 50 mK despite a Curie-Weiss Temperature thetaCW approximately -14 K. In this Letter we reinvestigate the theoretical description of this material by considering a quantum model of independent tetrahedra to describe its low-Temperature properties. The naturally tuned proximity of this system near a Neel to spin ice phase boundary allows for a resurgence of quantum fluctuation effects that lead to an important renormalization of its effective low-energy spin Hamiltonian. As a result, Tb2Ti2O7 is argued to be a quantum spin ice. We put forward an experimental test of this proposal using neutron scattering on a single crystal.
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thermodynamic and single ion properties of tb3 within the collective paramagnetic spin liquid state of the frustrated pyrochlore antiferromagnet tb2ti2o7
Physical Review B, 2000Co-Authors: Michel J P Gingras, B Den C Hertog, M Faucher, J S Gardner, S R Dunsiger, L J Chang, B D Gaulin, N P RajuAbstract:In a recent letter [Phys. Rev. Lett. {\bf 82}, 1012 (1999)] it was found that the Tb$^{3+}$ magnetic moments in the Tb$_2$Ti$_2$O$_7$ pyrochlore lattice of corner-sharing tetrahedra remain in a {\it collective paramagnetic} state down to 70mK. In this paper we present results from d.c. magnetic susceptibility, specific heat data, inelastic neutron scattering measurements, and crystal field calculations that strongly suggest that (1) the Tb$^{3+}$ ions in Tb$_2$Ti$_2$O$_7$ possess a moment of approximatively 5$\mu_{\rm B}$, and (2) the ground state $g-$tensor is extremely anisotropic below a Temperature of $O(10^0)$K, with Ising-like Tb$^{3+}$ magnetic moments confined to point along a local cubic $ $ diagonal (e.g. towards the middle of the tetrahedron). Such a very large easy-axis Ising like anisotropy along a $ $ direction dramatically reduces the frustration otherwise present in a Heisenberg pyrochlore antiferromagnet. The results presented herein underpin the conceptual difficulty in understanding the microscopic mechanism(s) responsible for Tb$_2$Ti$_2$O$_7$ failing to develop long-range order at a Temperature of the order of the paramagnetic Curie-Weiss Temperature $\theta_{\rm CW} \approx -10^1$K. We suggest that dipolar interactions and extra perturbative exchange coupling(s)beyond nearest-neighbors may be responsible for the lack of ordering of Tb$_2$Ti$_2$O$_7$.
Tiffany Smith M Pellizzeri - One of the best experts on this subject based on the ideXlab platform.
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single crystal neutron and magnetic measurements of rb2mn3 vo4 2co3 and k2co3 vo4 2co3 with mixed honeycomb and triangular magnetic lattices
Dalton Transactions, 2020Co-Authors: Tiffany Smith M Pellizzeri, Liurukara D Sanjeewa, Steven Pellizzeri, Colin D Mcmillen, Ovidiu V Garlea, A S Sefat, Joseph W KolisAbstract:Two new alkali vanadate carbonates with divalent transition metals have been synthesized as large single crystals via a high-Temperature (600 °C) hydrothermal technique. Compound I, Rb2Mn3(VO4)2CO3, crystallizes in the trigonal crystal system in the space group P1c, and compound II, K2Co3(VO4)2CO3, crystallizes in the hexagonal space group P63/m. Both structures contain honeycomb layers and triangular lattices made from edge-sharing MO6 octahedra and MO5 trigonal bipyramids, respectively. The honeycomb and triangular layers are connected along the c-axis through tetrahedral [VO4] groups. The MO5 units are connected with each other by carbonate groups in the ab-plane by forming a triangular magnetic lattice. The difference in space groups between I and II was also investigated with Density Functional Theory (DFT) calculations. Single crystal magnetic characterization of I indicates three magnetic transitions at 77 K, 2.3 K, and 1.5 K. The corresponding magnetic structures for each magnetic transition of I were determined using single crystal neutron diffraction. At 77 K the compound orders in the MnO6-honeycomb layer in a Neel-type antiferromagnetic orientation while the MnO5 triangular lattice ordered below 2.3 K in a colinear ‘up–up–down’ fashion, followed by a planar ‘Y’ type magnetic structure. K2Co3(VO4)2CO3 (II) exhibits a canted antiferromagnetic ordering below TN = 8 K. The Curie–Weiss fit (200–350 K) gives a Curie–Weiss Temperature of −42 K suggesting a dominant antiferromagnetic coupling in the Co2+ magnetic sublattices.
Joseph W Kolis - One of the best experts on this subject based on the ideXlab platform.
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single crystal neutron and magnetic measurements of rb2mn3 vo4 2co3 and k2co3 vo4 2co3 with mixed honeycomb and triangular magnetic lattices
Dalton Transactions, 2020Co-Authors: Tiffany Smith M Pellizzeri, Liurukara D Sanjeewa, Steven Pellizzeri, Colin D Mcmillen, Ovidiu V Garlea, A S Sefat, Joseph W KolisAbstract:Two new alkali vanadate carbonates with divalent transition metals have been synthesized as large single crystals via a high-Temperature (600 °C) hydrothermal technique. Compound I, Rb2Mn3(VO4)2CO3, crystallizes in the trigonal crystal system in the space group P1c, and compound II, K2Co3(VO4)2CO3, crystallizes in the hexagonal space group P63/m. Both structures contain honeycomb layers and triangular lattices made from edge-sharing MO6 octahedra and MO5 trigonal bipyramids, respectively. The honeycomb and triangular layers are connected along the c-axis through tetrahedral [VO4] groups. The MO5 units are connected with each other by carbonate groups in the ab-plane by forming a triangular magnetic lattice. The difference in space groups between I and II was also investigated with Density Functional Theory (DFT) calculations. Single crystal magnetic characterization of I indicates three magnetic transitions at 77 K, 2.3 K, and 1.5 K. The corresponding magnetic structures for each magnetic transition of I were determined using single crystal neutron diffraction. At 77 K the compound orders in the MnO6-honeycomb layer in a Neel-type antiferromagnetic orientation while the MnO5 triangular lattice ordered below 2.3 K in a colinear ‘up–up–down’ fashion, followed by a planar ‘Y’ type magnetic structure. K2Co3(VO4)2CO3 (II) exhibits a canted antiferromagnetic ordering below TN = 8 K. The Curie–Weiss fit (200–350 K) gives a Curie–Weiss Temperature of −42 K suggesting a dominant antiferromagnetic coupling in the Co2+ magnetic sublattices.
Woong Kil Choo - One of the best experts on this subject based on the ideXlab platform.
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electrical and magnetic properties of spinel type magnetic semiconductor znco2o4 grown by reactive magnetron sputtering
Journal of Applied Physics, 2004Co-Authors: In Chang Song, Woong Kil ChooAbstract:We report on the growth of spinel ZnCo2O4 films using reactive magnetron sputtering and their electrical and magnetic properties, with particular emphasis on the relation of Curie–Weiss Temperature (TCW) and conduction type. The conduction type and carrier concentration in these films were found to be dependent on the oxygen partial pressure ratio in the sputtering gas mixture. The highest electron and hole concentration at 300 K were 1.37×1020 and 2.81×1020 cm−3, respectively. A ferromagnetic coupling (TCW>0) was observable in p-type ZnCo2O4, whereas an antiferromagnetic interaction (TCW<0) was found for n-type and insulating ZnCo2O4, revealing hole-induced ferromagnetic transition in ZnCo2O4.
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magnetic properties of epitaxially grown semiconducting zn1 xcoxo thin films by pulsed laser deposition
Journal of Applied Physics, 2002Co-Authors: Jae Hyun Kim, Hyojin Kim, Dojin Kim, Young Eon Ihm, Woong Kil ChooAbstract:We have characterized Zn1−xCoxO (x=0.25) films grown on sapphire (0001) substrates by pulsed laser deposition using various growth conditions to investigate the growth condition dependence of properties of Co-doped ZnO films. The substrate Temperature (TS) was varied from 300 to 700 °C and the O2 pressure (PO2) from 10−6 to 10−1 Torr. When TS is relatively low (≲600 °C), homogeneous alloy films with a wurtzite ZnO structure are grown and predominantly paramagnetic, whereas inhomogeneous films of wurtzite ZnO phase mixed with rock-salt CoO and hexagonal Co phases form when TS is relatively high and PO2 is fairly low (≲10−5 Torr). The presence of Co clusters leads to room Temperature ferromagnetism in inhomogeneous films. The Temperature dependence of the magnetization for the homogeneous Zn1−xCoxO (x=0.25) films shows spin-glass behavior at low Temperature and high Temperature Curie–Weiss behavior with a large negative value of the Curie–Weiss Temperature, indicating strong antiferromagnetic exchange coupl...
