Estimation of single ion anisotropy in pyrochlore Dy2Ti2O7, a geometrically frustrated system, using crystal field theory

Jana, Yatramohan; Sengupta, A.; Ghosh, D.

doi:10.1016/s0304-8853(01)00983-0

Cited by 46 publications

(20 citation statements)

References 30 publications

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“…This was confirmed by Flood (1974) from direct measurement of the magnetic moment and from analysis of inelastic neutron scattering data by Rosenkranz (Rosenkranz et al, 2000). Calculations from crystal field theory, complemented by fitting crystal field parameters (CFPs) to susceptibility data also confirmed the strong Ising nature of Dy 3+ in Dy 2 Ti 2 O 7 (Jana et al, 2002). Specifically, the single ion electronic ground state of Dy 3+ is a Kramers doublet of almost pure |J = 15/2, m J = ±15/2 separated from the first excited state by a gap ∆ ≈ 33 meV (∼ 380 K) while the rescaled CFPs of Rosenkranz et al (2000) and Jana et al (2002) finds a much smaller excitation gap ∆ ≈ 100 cm −1 (∼ 140 K).…”

Section: A Dy2ti2o7 and Ho2ti2o7mentioning

confidence: 73%

Magnetic pyrochlore oxides

2010

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Within the past 20 years or so, there has occurred an explosion of interest in the magnetic behavior of pyrochlore oxides of the type A 3+ 2 B 4+ 2 O 7 where A is a rare-earth ion and B is usually a transition metal. Both the A and B sites form a network of corner-sharing tetrahedra which is the quintessential framework for a geometrically frustrated magnet. In these systems the natural tendency to form long range ordered ground states in accord with the Third Law is frustrated, resulting in some novel short range ordered alternatives such as spin glasses, spin ices and spin liquids and much new physics. This article attempts to review the myriad of properties found in pyrochlore oxides, mainly from a materials perspective, but with an appropriate theoretical context.

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Section: A Dy2ti2o7 and Ho2ti2o7mentioning

confidence: 73%

Magnetic pyrochlore oxides

2010

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“…Here, we use the temperaturerescaled c ph of the non-magnetic Y 2 Ti 2 O 7 and check the reliability of our procedure by measuring the specific heat of all (Dy 1-x Y x ) 2 Ti 2 O 7 samples in B = 0.5 and 1 T applied along the [100] direction. For this direction, field strengths between 0.5 and 1 T are, on the one hand side, sufficient to reach a fully saturated mag-netization at T ≃ 0.5 K. On the other hand, such fields are still low enough to reach the full entropy S ∞ of a two-level system around 25 K, where the thermal population of higher-lying crystal field levels is still negligible [33,34]. Figure 3 summarizes the magnetic entropy of the series (Dy 1-x Y x ) 2 Ti 2 O 7 .…”

Section: Fig 2 (Color Online) (A) Specific Heat C(t ) Per Formula Unitmentioning

confidence: 99%

Suppression of Pauling's residual entropy in the dilute spin ice(Dy1−xYx)2Ti2
Scharffe
¹
,
Breunig
²
,
Cho
³

et al. 2015
Phys. Rev. B

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Around 0.5 K, the entropy of the spin-ice Dy2Ti2O7 has a plateau-like feature close to Pauling's residual entropy derived originally for water ice, but an unambiguous quantification towards lower temperature is prevented by ultra-slow thermal equilibration. Based on specific heat data of (Dy1-xYx)2Ti2O7 we analyze the influence of non-magnetic dilution on the low-temperature entropy. With increasing x, the ultra-slow thermal equilibration rapidly vanishes, the low-temperature entropy systematically decreases and its temperature dependence strongly increases. These data suggest that a non-degenerate ground state is realized in (Dy1-xYx)2Ti2O7 for intermediate dilution.This contradicts the expected zero-temperature residual entropy obtained from a generalization of Pauling's theory for dilute spin ice, but is supported by Monte Carlo simulations. Spin-ice materials attract lots of attention due to their exotic ground state and anomalous excitations [1][2][3][4][5][6][7][8], which arise from a geometric frustration of the magnetic interactions that prevents long-range magnetic order. Prototype spin-ice materials are the pyrochlores R 2 Ti 2 O 7 with Dy or Ho as R 3+ ions, which form a network of corner-sharing tetrahedra. The crystal electric field causes a strong Ising anisotropy with local quantization axes pointing from each corner of a tetrahedron to its center. Thus, each magnetic moment is restricted to one of the {111} directions and may point only either into or out of the tetrahedron. The energy of antiferromagnetic exchange and dipole-dipole interactions is minimized when two spins point into and the other two point out of each tetrahedron. This '2in/2out' ground state is 6-fold degenerate and fulfills Pauling's ice rule describing the hydrogen displacement in water ice with the residual entropy S P = (N A k B /2) ln(3/2) [9,10]. Excitations are created by single spin flips resulting in pairs of tetrahedra with '3in/1out' and '1in/3out' configurations. As a consequence of the ground-state degeneracy, each pair fractionalizes into two individual excitations that can be described as magnetic (anti-)monopoles propagating independently through the lattice [3,4,11,12]. The dynamics of these monopole excitations is subject of intense research [5,[13][14][15][16].Experimental evidence for Pauling's residual entropy in spin-ice systems stems from specific heat measurements [17][18][19][20] reporting a practically temperatureindependent entropy S ex (T ≈ 0.4 K) ≃ S P . More recently, however, extremely slow relaxation phenomena were observed for Dy 2 Ti 2 O 7 in low-temperature measurements of, e.g., the magnetization [21,22], ac susceptibility [23], thermal transport [24,25] or the specific heat [24,26,27]. Typically, these phenomena set in below ≈ 0.6 K and signal strongly increasing timescales for the internal thermal equilibration. Therefore, the specificheat values obtained by standard relaxation-time techniques are too low and S ex (T < 0.5 K) < S P was reported for thermally equilibrated Dy 2 Ti 2 O 7 [27]....

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“…2). The trigonal crystal field enforces a doublet ground state for each ion [53][54][55][56] and establishes a local Ising-like [56] confinement with effective two-state spins S i pointing between the centers of each pair of adjacent tetrahedra. The associated magnetic moments are very large, µ ≈ 10 µ B , with the consequence that dipole-dipole interactions are particularly strong in these materials.…”

Section: Numerical Simulationsmentioning

confidence: 99%

Screening and the pinch point paradox in spin ice

Twengström

Henelius

Bramwell

2020

Phys. Rev. Research

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A pinch point singularity in the structure factor characterizes an important class of condensed matter that is a counterpoint to the paradigm of broken symmetry. This class includes water ice, charge ice and spin ice. Of these, dipolar spin ice affords the the pre-eminent model system because it has a well-established Hamiltonian, is simple enough to allow analytical theory and numerical simulation, and is well represented in experiment by Dy2Ti2O7 and Ho2Ti2O7. Nevertheless it is a considerable challenge to resolve the pinch points in simulation or experiment as they represent a very long range correlation. Here we present very high resolution simulations of the polarized neutron scattering structure factor of dipolar spin ice and new analytical theory of the pinch point profiles. We compare these with existing theory and experiment. We find that our simulations are consistent with theories that reveal the pinch points to be infinitely sharp, as a result of unscreened dipolar fields. However, neither simulation nor these theories are consistent with experiments, which instead is quantitatively captured by a theory that allows for screening of the dipolar fields and consequent strong broadening of the pinch points. This striking paradox is not easily resolved: broadening of the pinch points by random disorder seems to have been ruled out by existing theory, while deficiencies in the Hamiltonian description are not relevant. Intriguingly, we are left to consider the role of quantum fluctuations or the possibility of a fundamental correction to either the standard method of simulating dipolar systems, or the theory of polarized neutron scattering. More generally, our results may have relevance far beyond ice systems. For example, spin ice is a model Debye-Hückel (magnetic) electrolyte, so our basic observation that the screening length may diverge while the Debye length remains constant, may hint at a solution to the topical problem of 'underscreening' in concentrated ionic liquids.

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Estimation of single ion anisotropy in pyrochlore Dy2Ti2O7, a geometrically frustrated system, using crystal field theory

Cited by 46 publications

References 30 publications

Magnetic pyrochlore oxides

Magnetic pyrochlore oxides

Suppression of Pauling's residual entropy in the dilute spin ice(Dy1−xYx)2Ti2
Scharffe
¹
,
Breunig
²
,
Cho
³

et al. 2015
Phys. Rev. B

Screening and the pinch point paradox in spin ice

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Estimation of single ion anisotropy in pyrochlore Dy2Ti2O7, a geometrically frustrated system, using crystal field theory

Cited by 46 publications

References 30 publications

Magnetic pyrochlore oxides

Magnetic pyrochlore oxides

Suppression of Pauling's residual entropy in the dilute spin ice(Dy1−xYx)2Ti2Scharffe1, Breunig2, Cho3 et al. 2015Phys. Rev. B

Screening and the pinch point paradox in spin ice

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Suppression of Pauling's residual entropy in the dilute spin ice(Dy1−xYx)2Ti2
Scharffe
¹
,
Breunig
²
,
Cho
³

et al. 2015
Phys. Rev. B