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Fennell, T.; Petrenko, O. A.; Fåk, B.; Bramwell, S. T.; Enjalran, Matthew; Yavors’kii, T.; Gingras, Michel J. P.; Melko, Roger G.; Balakrishnan, G.

doi:10.1103/physrevb.70.134408

Cited by 72 publications

(85 citation statements)

References 33 publications

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“…However, adding a very small antiferromagnetic third nearest-neighbor exchange J 3 = −0.022 K gives a transition to a ferromagnetic ground state at a temperature close to the experimental value of 0.35 K. Interestingly, an antiferromagnetic J 3 of this magnitude (−0.03K < J 3 < −0.01K) appears able to explain the paramagnetic zone boundary scattering observed in neutron scattering of Dy 2 Ti 2 O 7 [17]. A more antiferromagnetic (negative) J 3 changes the ordered state to a Néel state with ordering wavevector q = (1/2, 1/2, 0).…”

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confidence: 87%

“…It is now well established that the nearest-neighbor exchange in Ho 2 Ti 2 O 7 [6] and Dy 2 Ti 2 O 7 [15,16,17] is antiferromagnetic and that the spin-ice phenomenon originates from long-range magnetic dipole-dipole interactions rather than from nearest-neighbor ferromagnetic exchange as originally proposed [1,2]. The magnetic moment, µ eff , of Ho 3+ and Dy 3+ in the above materials is µ eff ∼ 10µ B , giving a dipolar coupling constant, D, at nearest-neighbor distance of approximately 1.4 K [6,15].…”

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confidence: 99%

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Finite-Temperature Transitions in Dipolar Spin Ice in a Large Magnetic Field

2005

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We use Monte Carlo simulations to identify the mechanism that allows for phase transitions in dipolar spin ice to occur and survive for applied magnetic field, H, much larger in strength than that of the spin−spin interactions. In the most generic and highest symmetry case, the spins on one out of four sublattices of the pyrochlore decouple from the total local exchange+dipolar+applied field. In the special case where H is aligned perfectly along the [110] crystallographic direction, spin chains perpendicular to H show a transition to q = X long range order, which proceeds via a one to three dimensional crossover. We propose that these transitions are relevant to the origin of specific heat features observed in powder samples of the Dy2Ti2O7 spin ice material for H above 1 Tesla. [5]. For a field H larger than 1 Tesla (T), a sharp peak suggesting a phase transition occurs at a field-independent temperature of 0.35 K, surviving up to the largest field considered (6 T). Another rounded peak at 1.2 K first appears at 0.75 T and also remains observable up to 6 T, although it is less sharp than the 0.35 K feature. Finally, a third peak at 0.5 K first appears at 1 T, where it is quite sharp, but disappears for H > ∼ 3 T. Over the past six years, much theoretical effort has been devoted to the search for a microscopic explanation of the field-induced spin correlations responsible for these specific heat fea- suggested that some of these features might be due to phase transitions arising in crystallites that accidently happen to be oriented such that some of the Ising spins in the unit cell are perpendicular to H. These "fielddecoupled" spins would then be free to interact among themselves, giving transitions at temperatures that are field-independent up to a very large field [5]. A similar proposal had been made earlier for the case of garnet systems [9]. Experimental evidence [10] suggests that the 0.5 K feature in powder samples arises due to a multicritical point at a temperature of 0.5 K and field of 1 T along the [111] crystallographic direction, which is related to the interesting phenomenology of kagomé ice [11]. However, to date, there is no concensus as to whether or not the specific heat features at 0.35 K and 1.2 K are caused by the magnetic field directed on crystallites of particular orientation [12,13,14]. In this paper we address this question by using the dipolar spin ice model, where Ising spins

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Finite-Temperature Transitions in Dipolar Spin Ice in a Large Magnetic Field

2005

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“…Acsusceptibility studies of powdered Dy 2 Ti 2 O 7 up to 20 K suggest rather a wide distribution of relaxation times 18 , but other studies 19 suggest that spin ice responds to external magnetic field in a very limited range of relaxation times, an effect that has been ascribed to the high degree of chemical and structural order. In addition, acsusceptibility data for Dy 2 Ti 2 O 7 indicate strongly frequency dependent spin freezing at about 16 K. This was initially discussed in terms of collective dynamics, 19,20 , but subsequently, on the basis of systematic studies of Dy 2−x Y x Ti 2 O 7 in wide range of dilutions x 21 as well as neutron scattering 22 , ascribed to a single spin flip process.…”

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confidence: 99%

Magnetocaloric study of spin relaxation in dipolar spin iceDy2Ti2O7

et al. 2007

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The magnetocaloric effect of polycrystalline samples of pure and Y-doped dipolar spin ice Dy2Ti2O7 was investigated at temperatures from nominally 0.3 K to 6 K and in magnetic fields of up to 2 T. As well as being of intrinsic interest, it is proposed that the magnetocaloric effect may be used as an appropriate tool for the qualitative study of slow relaxation processes in the spin ice regime. In the high temperature regime the temperature change on adiabatic demagnetization was found to be consistent with previously published entropy versus temperature curves. At low temperatures (T < 0.4 K) cooling by adiabatic demagnetization was followed by an irreversible rise in temperature that persisted after the removal of the applied field. The relaxation time derived from this temperature rise was found to increase rapidly down to 0.3 K. The data near to 0.3 K indicated a transition into a metastable state with much slower relaxation, supporting recent neutron scattering results. In addition, magnetic dilution of 50 % concentration was found to significantly prolong the dynamical response in the milikelvin temperature range, in contrast with results reported for higher temperatures at which the spin correlations are suppressed. These observations are discussed in terms of defects and loop correlations in the spin ice state.

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“…The Dy 2 Ti 2 O 7 crystal [26] is somewhat smaller ( 1.5 g) because it is isotopically enriched with 162 Dy to reduce the large absorption cross section of natural isotopic abundance dysprosium. It is the same crystal used for the measurement of magnetic diffuse scattering [27], but before the LD study it was reannealed in oxygen to eliminate possible oxygen vacancies [28]. All samples were mounted on ultrapure copper mounts to ensure good equilibration.…”

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confidence: 99%

Neutron Larmor diffraction investigation of the rare-earth pyrochlores R2Ti2O7 ( R=Tb , Dy, Ho

et al. 2016

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In this work, we present a neutron Larmor diffraction study of the rare-earth pyrochlores R 2 Ti 2 O 7 with R = Tb, Dy, Ho. We measured the temperature dependence of the lattice parameter with precision 10 −5 , between 0.5 and 300 K in each of the three compounds. The lattice parameter of the spin ices Dy 2 Ti 2 O 7 and Ho 2 Ti 2 O 7 enters into the derivation of the charge of the emergent magnetic monopole excitations suggested to exist in these materials. We found that throughout the range of applicability of the theory of emergent monopoles in the spin ices there will be no renormalization of the monopole charge due to lattice contraction. In Tb 2 Ti 2 O 7 , strong magnetoelastic interactions have been reported. We found no sign of the previously reported negative thermal expansion, but did observe anomalies in the thermal expansion that can be correlated with previously observed interactions between phonon and crystal-field excitations. Other features in the thermal expansion of all three compounds can be related to previously observed anomalies of the elastic constants, and explained by the phonon band structure of the rare-earth titanates. The temperature dependence of the lattice strain in all three compounds can be correlated with the thermal population of excited crystal-field levels.

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Neutron scattering investigation of the spin ice state inDy2Ti2O7

Cited by 72 publications

References 33 publications

Finite-Temperature Transitions in Dipolar Spin Ice in a Large Magnetic Field

Finite-Temperature Transitions in Dipolar Spin Ice in a Large Magnetic Field

Magnetocaloric study of spin relaxation in dipolar spin iceDy2Ti2O7

Neutron Larmor diffraction investigation of the rare-earth pyrochlores R2Ti2O7 ( R=Tb , Dy, Ho

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