Single-crystal versus polycrystalline samples of magnetically frustrated Yb<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>2</mml:mn></mml:msub></mml:math>Ti<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>2</mml:mn></mml:msub></mml:math>O<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>7</mml:mn></mml:msub></mml:math>: Specific heat results

Yaouanc, A.; Réotier, P. Dalmas de; Marı́n, C.; Glazkov, V. N.

doi:10.1103/physrevb.84.172408

Cited by 84 publications

(131 citation statements)

References 37 publications

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“…a sharp change in the spin dynamics at T c in zero field [36]. Signatures of shortrange magnetic correlations both in the paramagnetic state through a specific-heat measurement [34] and in the ordered state from µSR data [50,51] have been found. Short-range correlations in the ordered state were certainly unexpected.…”

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confidence: 85%

“…In addition to the sample quality issue first noticed in Ref. [34], the low temperature required for the observation of neutron magnetic Bragg reflections is an additional issue. This is particularly true for a powder sample as illustrated by the sibling compound Yb 2 Sn 2 O 7 for which only two out of the three powder neutron diffraction studies have reported the existence of magnetic reflections [37,38,39].…”

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confidence: 99%

“…[27,31] which describe data measured on the same crystal. The diversity of the specific heat [33,34,31,35] and muon spin relaxation (µSR) results [22,36,25,23] adds to the difficulty in understanding the ground state. In addition to the sample quality issue first noticed in Ref.…”

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confidence: 99%

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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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A novel type of splayed ferromagnetic order observed in Yb₂Ti₂O₇

Yaouanc

Réotier

Keller

et al. 2016

J. Phys.: Condens. Matter

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“…Stoichiometric Yb 2 Ti 2 O 7 is known to display a large and sharp anomaly in its heat capacity, C p , near ∼ 265 mK. However, this anomaly has been observed to be sample dependent with samples displaying broader anomalies at lower temperatures depending on the exact stoichiometry of the material studied [24][25][26][27][28] . This phenomena is very unusual for a three dimensional magnet, as the defect levels involved are at the limits of detectability by conventional…”

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confidence: 99%

Neutron spectroscopic study of crystalline electric field excitations in stoichiometric and lightly stuffedYb2Ti2O7

et al. 2015

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Time-of-flight neutron spectroscopy has been used to determine the crystalline electric field (CEF) Hamiltonian, eigenvalues and eigenvectors appropriate to the J = 7/2 Yb 3+ ion in the candidate quantum spin ice pyrochlore magnet Yb2Ti2O7. The precise ground state (GS) of this exotic, geometrically-frustrated magnet is known to be sensitive to weak disorder associated with the growth of single crystals from the melt. Such materials display weak "stuffing" wherein a small proportion, ≈ 2%, of the non-magnetic Ti 4+ sites are occupied by excess Yb 3+ . We have carried out neutron spectroscopic measurements on a stoichiometric powder sample of Yb2Ti2O7, as well as a crushed single crystal with weak stuffing and an approximate composition of Yb2+xTi2−xO7+y with x = 0.046. All samples display three CEF transitions out of the GS, and the GS doublet itself is identified as primarily composed of mJ = ±1/2, as expected. However,"stuffing" at low temperatures in Yb2+xTi2−xO7+y induces a similar finite CEF lifetime as is induced in stoichiometric Yb2Ti2O7 by elevated temperature. We conclude that an extended strain field exists about each local "stuffed" site, which produces a distribution of random CEF environments in the lightly stuffed Yb2+xTi2−xO7+y, in addition to producing a small fraction of Yb-ions in defective environments with grossly different CEF eigenvalues and eigenvectors.

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“…Yb 2 Ti 2 O 7 was originally thought to be a type of XY -ferromagnet on the pyrochlore lattice [125,126], but definitive evidence of static order below a phase transition at 0.24 K remained conflicting [24,[126][127][128]. This was compounded by irregular existence of the phase transition in different samples [129,130] which is now attributed to very small variations in stoichiometry [130,131]. Above this temperature is a cooperative paramagnet phase [132,133] has become the most popular candidate quantum spin ice [121,124,131,134].…”

Section: Yb 2 Ti 2 Omentioning

confidence: 94%

Neutron scattering studies of spin ices and spin liquids

Fennell

2014

Journées de la Neutronique

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Abstract. In frustrated magnets, competition between interactions, usually due to incompatible lattice and exchange geometries, produces an extensively degenerate manifold of groundstates. Exploration of these states results in a highly correlated and strongly fluctuating cooperative paramagnet, a broad classification which includes phases such as spin liquids and spin ices. Generally, there is no long range order and associated broken symmetry, so quantities typically measured by neutron scattering such as magnetic Bragg peaks and magnon dispersions are absent. Instead, spin correlations characterized by emergent gauge structure and exotic fractional quasiparticles may emerge. Neutron scattering is still an excellent tool for the investigation these phenomena, and this review outlines examples of frustrated magnets on the pyrochlore and kagome lattices with reference to experiments and quantities of interest for neutron scattering. PREAMBLEIn physics, a frustrated system is one in which all interactions cannot be simultaneously minimized, which is also to say that there is competition amongst the interactions. Frustration is most commonly associated with spin systems [1], where its consequences can be particularly well identified, but is by no means limited to magnetism. Frustrated interactions are also relevant in certain structural problems [2][3][4][5][6] Interest in frustrated spin systems stems from the idea that conventional order will be suppressed by the frustration, and an unconventional state will appear in its place. For example, Anderson proposed that in high temperature superconductors, antiferromagnetic Néel ordering would be replaced by a resonating valence bond state (RVB) [17], which would host the superconductivity on doping. If the RVB state could be promoted by enhancing frustration, a route to high(er)-T c materials might appear. This has never been realized, and understanding the character of the "unconventional" states, particularly the quantum spin liquid, which emerge in frustrated magnets is usually the objective of current studies.Extensive reviews of topics in frustrated magnetism can be found in the books edited by Lacroix, Mendels and Mila [1], and by Diep [18]. Topics recently reviewed in the literature include quantum spin liquids [19,20]; various aspects of spin ice [21][22][23]; rare earth pyrochlores [24], spinels [25]; and spin ices and kagome spin liquids have their own chapters in Ref. [1]. In the following, I present a brief This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Single-crystal versus polycrystalline samples of magnetically frustrated Yb2Ti2O7: Specific heat results

Cited by 84 publications

References 37 publications

A novel type of splayed ferromagnetic order observed in Yb₂Ti₂O₇

A novel type of splayed ferromagnetic order observed in Yb₂Ti₂O₇

Neutron spectroscopic study of crystalline electric field excitations in stoichiometric and lightly stuffedYb2Ti2O7

Neutron scattering studies of spin ices and spin liquids

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Single-crystal versus polycrystalline samples of magnetically frustrated Yb2Ti2O7: Specific heat results

Cited by 84 publications

References 37 publications

A novel type of splayed ferromagnetic order observed in Yb2Ti2O7

A novel type of splayed ferromagnetic order observed in Yb2Ti2O7

Neutron spectroscopic study of crystalline electric field excitations in stoichiometric and lightly stuffedYb2Ti2O7

Neutron scattering studies of spin ices and spin liquids

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A novel type of splayed ferromagnetic order observed in Yb₂Ti₂O₇

A novel type of splayed ferromagnetic order observed in Yb₂Ti₂O₇