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# Absence of long-range magnetic ordering in the pyrochlore compound Er2Sn2O7

Department of Chemistry, University of Winnipeg, Winnipeg, MB, R3B 2E9, Canada.
(Impact Factor: 2.22). 09/2011; 23(38):382201. DOI: 10.1088/0953-8984/23/38/382201
Source: PubMed

ABSTRACT The low temperature behaviour of powder Er2Sn2O7 samples has been studied by magnetic susceptibility, heat capacity, and neutron scattering experiments. We report here the absence of magnetic ordering down to 100 mK. Anomalies in the heat capacity can be accounted for through an analysis of the crystal field spectrum observed by inelastic neutron scattering spectroscopy. These new measurements on Er2Sn2O7 suggest a new lower bound for the frustration index of f = |Θ(CW)|/T(N) = 14/0.1 = 140, placing this compound into a highly frustrated regime.

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##### Article: Magnetic ground-state of strongly frustrated pyrochlore anti-ferromagnet Er2Sn2O7
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ABSTRACT: The experimental results of bulk magnetic susceptibility, isothermal magnetization and magnetic specific heat of the frustrated anti-ferromagnetic pyrochlore Er2Sn2O7 are simulated and analyzed using appropriate crystal-field (CF) and molecular field tensors at Er-sites in the mean-field approach, which are found to be anisotropic along and normal to the local 〈111〉 axis of the frustrated tetrahedral spin-structure. Er-spins are constrained to lie in the local [111] easy-plane in the anti-ferromagnetic phase. Isothermal magnetization can be described by angle-averaged magnetization of the polycrystalline sample, expressed in terms of anisotropic g-tensors and exchange tensors. Temperature-dependent characteristic exchange splitting of the single-ion ground doublet describes the magnetic specific heat satisfactorily. The smaller exchange-splitting may cause rapid fluctuations of Er-spin moments in Er2Sn2O7 and hence long-range ordering of Er-spins is not exhibited by Er2Sn2O7 down to 100 mK, unlike in Er2Ti2O7.
Journal of Magnetism and Magnetic Materials 06/2014; 361:175–181. DOI:10.1016/j.jmmm.2014.02.086 · 2.00 Impact Factor
• ##### Article: Long-range antiferromagnetic order in the frustrated XY pyrochlore antiferromagnet Er 2 Ge 2 O 7
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ABSTRACT: A cubic Er2Ge2O7 pyrochlore was prepared under high-pressure and high-temperature conditions and its magnetic ground state was investigated by measurements of specific heat, dc and ac magnetic susceptibility as functions of temperature, pressure, and magnetic field. We found that Er2Ge2O7 undergoes a long-range antiferromagnetic transition at TN ≈ 1.4 K, which can be further enhanced by applying external physical pressure. On the other hand, application of external magnetic fields suppresses the antiferromagnetic order to zero temperature around Hc ≈ 2.3 T, where a magnetic-field-induced spin-flop transition was observed. Hc increases accordingly with increasing TN under external pressure. A comparison of the magnetic ground states and structural variations along the isostructural series Er2B2O7 (B = Sn, Ti, Ge) together with the high-pressure study on Er2Ge2O7 indicated that the magnetic properties of these highly frustrated XY pyrochlore antiferromagnets are very sensitive to the minute structural changes that determine the anisotropic exchange interactions and the local crystal-electric-field environments of Er3+ ions.
Physical Review B 02/2014; 89(6):064409. DOI:10.1103/PhysRevB.89.064409 · 3.66 Impact Factor
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##### Article: Ground State Phase Diagram of Generic XY Pyrochlore Magnets with Quantum Fluctuations
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ABSTRACT: Motivated by recent experimental and theoretical progress on the Er2Ti2O7 pyrochlore XY antiferromagnet, we study the problem of quantum order-by-disorder in pyrochlore XY systems. We consider the most general nearest-neighbor pseudo spin-1/2 Hamiltonian for such a system characterized by anisotropic spin-spin couplings J_e = [J_\pm, J_{\pm\pm}, J_{z\pm}, J_{zz}] and construct zero-temperature phase diagrams. Combining symmetry arguments and spin-wave calculations, we show that the ground state phase boundaries between the two candidate ground states of the \Gamma_5 irreducible representation, the \psi_2 and \psi_3 (basis) states, are rather accurately determined by a cubic equation in J_{\pm}J_{\pm\pm})/J_{z\pm}^2. Depending on the value of J_{zz}, there can be one or three phase boundaries that separate alternating regions of \psi_2 and \psi_3 states. In particular, we find for sufficiently small J_{zz}/J_{\pm} a narrow \psi_2 sliver sandwiched between two \psi_3 regions in the J_{\pm\pm}/J_\pm vs J_{z\pm}/J_\pm phase diagram. Our results further illustrate the very large potential sensitivity of the ground state of XY pyrochlore systems to minute changes in their spin Hamiltonian. Using the experimentally determined J_3 and g-tensor values for Er2Ti2O7, we show that the heretofore neglected long-range 1/r^3 magnetostatic dipole-dipole interactions do not change the conclusion that Er2Ti2O7 has a \psi_2 ground state induced via a quantum order-by-disorder mechanism. We propose that the CdDy2Se4 chalcogenide spinel, in which the Dy^{3+} ions form a pyrochlore lattice and may be XY-like, could prove interesting to investigate.
Physical Review B 11/2013; 88(14). DOI:10.1103/PhysRevB.88.144402 · 3.66 Impact Factor