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Harris, Mark; Bramwell, S. T.; McMorrow, D. F.; Zeiske, Th.; Keller, Godfrey

doi:10.1103/physrevlett.79.2554

Cited by 1,102 publications

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“…As the temperature decreases, spin fluctuation becomes weaker and spin-phonon coupling stronger. It is important to notice that although ferromagnetic correlations are short ranged without long range order in spin ice compounds, from neutron scattering measurements Harris et al [18] have shown that the range of ferromagnetic order increases at lower temperature. As a result, spin-phonon coupling range is wider so that the phonon frequency shows redshift or blueshift, which is in agreement with what is observed in our optical conductivity spectra.…”

Section: Resultsmentioning

confidence: 99%

Far infrared optical properties of the pyrochlore spin ice compound Dy₂Ti₂O₇

Bi¹,

Y²,

Zhao³

et al. 2005

J. Phys.: Condens. Matter

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Abstract. Near normal incident far-infrared reflectivity spectra of [111] dysprosium titanate (Dy 2 Ti 2 O 7 ) single crystal have been measured at different temperatures. Seven phonon modes (eight at low temperature) are identified at frequency below 1000 cm −1 . Optical conductivity spectra are obtained by fitting all the reflectivity spectra with the factorized form of the dielectric function. Both the Born effective charges and the static optical primitivity are found to increase with decreasing temperature. Moreover, phonon linewidth narrowering and phonon modes shift with decreasing temperature are also observed, which may result from enhanced charge localization. The redshift of several low frequency modes is attributed to the spin-phonon coupling. All observed optical properties can be explained within the framework of nearest neighbor ferromagnetic(FM) spin ice model.

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Section: Resultsmentioning

confidence: 99%

Far infrared optical properties of the pyrochlore spin ice compound Dy₂Ti₂O₇

Bi¹,

Y²,

Zhao³

et al. 2005

J. Phys.: Condens. Matter

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“…These distinguished properties include a spin-glass state with very little, or no, structural disorder, 3,4 collective paramagnetism or spin-liquid behavior, 5 and the most interesting and extensively studied behavior of dipolar spin ice. [6][7][8][9] Among the pyrochlore oxide family, Ho 2 Ti 2 O 7 , Ho 2 Sn 2 O 7 , Dy 2 Ti 2 O 7 , and Dy 2 Sn 2 O 7 have been identified as spin-ice materials and they can be modeled by a spin model with an 111 Ising-type anisotropy and a net ferromagnetic interaction. [6][7][8][9][10] Tb 2 Ti 2 O 7 is a fluctuating spin-liquid state at low temperature 5,[11][12][13][14] and, to date, there exists no model that can adequately describe all the physical properties observed in Tb 2 Ti 2 O 7 .…”

Section: Introductionmentioning

confidence: 99%

Magnetic correlations in HoxTb2−xTi
Chang
¹
,
Schweika
²
,
Kao
³

et al. 2011
Phys. Rev. B
17
4
14
0
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Polycrystalline samples of Ho x Tb 2−x Ti 2 O 7 (0 < x < 2) have been prepared and characterized for their structural and magnetic properties. The parent compounds of this solid solution are the spin ice Ho 2 Ti 2 O 7 and the spin liquid Tb 2 Ti 2 O 7 . Specific-heat measurements on HoTbTi 2 O 7 (x = 1.0) reveal the absence of a long-range order state above 0.5 K. The integrated entropies of all Ho x Tb 2−x Ti 2 O 7 specimens up to 30 K scale well with the ratio of spin ice and spin liquid in the composition. The neutron diffraction spectrum of HoTbTi 2 O 7 exhibits a dipolar spin-ice pattern and can be well described by mean-field theory for 111 Ising spins, nearest-neighbor exchange, and dipolar interactions. Inelastic neutron scattering on HoTbTi 2 O 7 reveals two dispersionless excitations, one of ∼2.5 meV out of the ground state, and a 4-meV transition out of an excited state. We argue that these data suggest that the very strong single-ion effects of Ho 2 Ti 2 O 7 and Tb 2 Ti 2 O 7 persist in the Ho x Tb 2−x Ti 2 O 7 (0 < x < 2) solid solution, whereas the Tb-Ho correlations are weak, resulting in small shifts in the energy scales but with no dramatic effect on the bulk properties.

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“…As a consequence, classical and quantum fluctuations are particularly strong. Among the interactions of interest, the crystal field at the R position, the Heisenberg nearest-neighbour exchange interaction as well as its extension beyond the nearest-neighbour R ions [6,7], the anisotropy of the exchange interactions [8,9] and the inevitable dipolar interactions have been considered.The most remarkable discovery in the realm of geometrically frustrated magnetic materials has been the spin-ice ground state of Ho 2 Ti 2 O 7 in 1997 [10]. It is characterized by dipolar correlations emerging from the topological spin-ice constraint.…”

mentioning

confidence: 99%

“…The most remarkable discovery in the realm of geometrically frustrated magnetic materials has been the spin-ice ground state of Ho 2 Ti 2 O 7 in 1997 [10]. It is characterized by dipolar correlations emerging from the topological spin-ice constraint.…”

mentioning

confidence: 99%

A novel type of splayed ferromagnetic order observed in Yb₂Ti₂O₇

Yaouanc

Réotier

Keller

et al. 2016

J. Phys.: Condens. Matter

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Abstract. The pyrochlore insulator Yb 2 Ti 2 O 7 has attracted the attention of experimentalists and theoreticians alike for about 15 years. Conflicting neutron diffraction data on the possible existence of magnetic Bragg reflections at low temperature have been published. Here we report the observation of magnetic Bragg reflections by neutron powder diffraction at 60 mK. The magnetic diffraction pattern is analyzed using representation theory. We find Yb 2 Ti 2 O 7 to be a splayed ferromagnet as reported for Yb 2 Sn 2 O 7 , a sibling compound with also dominating ferromagnetic interactions as inferred from the positive Curie-Weiss temperature. However, the configuration of the magnetic moment components perpendicular to the easy axis is of the all-in-all-out type in Yb 2 Ti 2 O 7 while it is two-in-two-out in Yb 2 Sn 2 O 7 . An overall experimental picture of the magnetic properties emerges. Introduction -The broad interest in geometrically frustrated magnetic materials such as pyrochlore insulator compounds R 2 M 2 O 7 (F d3m space group), where R is a rare earth ion and M a non magnetic element, arises from the large diversity of magnetic ground states and exotic fluctuations and excitations encountered [1,2,3,4,5]. This is due to the combined effects of the geometrical constraint resulting from the topology of the pyrochlore lattice and the action of the different possible interactions. As a consequence, classical and quantum fluctuations are particularly strong. Among the interactions of interest, the crystal field at the R position, the Heisenberg nearest-neighbour exchange interaction as well as its extension beyond the nearest-neighbour R ions [6,7], the anisotropy of the exchange interactions [8,9] and the inevitable dipolar interactions have been considered.The most remarkable discovery in the realm of geometrically frustrated magnetic materials has been the spin-ice ground state of Ho 2 Ti 2 O 7 in 1997 [10]. It is characterized by dipolar correlations emerging from the topological spin-ice constraint. This translates into pinch-points in the neutron diffuse scattering patterns [11] and magnetic monopole excitations [12,13,14].Because of its large ground-state degeneracy, a spin-ice compound does not order magnetically, i.e., it is in a so-called spin liquid state where the spins are strongly correlated although they do not display long range order. Quantum fluctuations are not expected to play a significant role for Ho 2 Ti 2 O 7 . However, for some pyrochlore materials strong quantum transverse fluctuations [8,9] could stabilize new magnetic states such as a quantum spin liquid for which new exotic excitations are expected [3,15,16,17,5].One of the favourite candidates for this exotic ground state is Yb 2 Ti 2 O 7 . Indeed, the exchange interactions are highly anisotropic, with a strong ferromagnetic component akin to the Ising exchange of spin ice [18].The dominating ferromagnetic component is also suggested by the positive Curie-Weiss temperature [19]. Remarkably, the Ising character of the exchan...

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Geometrical Frustration in the Ferromagnetic PyrochloreHo2Ti2O7

Cited by 1,102 publications

References 15 publications

Far infrared optical properties of the pyrochlore spin ice compound Dy₂Ti₂O₇

Far infrared optical properties of the pyrochlore spin ice compound Dy₂Ti₂O₇

Magnetic correlations in HoxTb2−xTi
Chang
¹
,
Schweika
²
,
Kao
³

et al. 2011
Phys. Rev. B
17
4
14
0
View full text Add to dashboard Cite

A novel type of splayed ferromagnetic order observed in Yb₂Ti₂O₇

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Geometrical Frustration in the Ferromagnetic PyrochloreHo2Ti2O7

Cited by 1,102 publications

References 15 publications

Far infrared optical properties of the pyrochlore spin ice compound Dy2Ti2O7

Far infrared optical properties of the pyrochlore spin ice compound Dy2Ti2O7

Magnetic correlations in HoxTb2−xTiChang1, Schweika2, Kao3 et al. 2011Phys. Rev. B174140View full textAdd to dashboardCite

A novel type of splayed ferromagnetic order observed in Yb2Ti2O7

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Product

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About

Far infrared optical properties of the pyrochlore spin ice compound Dy₂Ti₂O₇

Far infrared optical properties of the pyrochlore spin ice compound Dy₂Ti₂O₇

Magnetic correlations in HoxTb2−xTi
Chang
¹
,
Schweika
²
,
Kao
³

et al. 2011
Phys. Rev. B
17
4
14
0
View full text Add to dashboard Cite

A novel type of splayed ferromagnetic order observed in Yb₂Ti₂O₇