Spin dynamics in geometrically frustrated compounds

Yaouanc, A.; Réotier, P. Dalmas de; Bonville, P.; Hodges, J.A.; Gubbens, P.C.M.; Kaiser, Christian; Sakarya, S.

doi:10.1016/s0921-4526(02)01664-2

Cited by 28 publications

(37 citation statements)

References 22 publications

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“…This Á para value is very close to that obtained in the isomorphous compound Yb 2 Ti 2 O 7 (80 mT) [38]. Below T t , i.e., in the presence of long-range magnetic order, it might be expected that the spectral shape would show rapid depolarization or pronounced oscillations due to muon spin precession in the spontaneous field [37].…”

Section: Prl 110 127207 (2013) P H Y S I C a L R E V I E W L E T T Esupporting

confidence: 80%

Dynamical Splayed Ferromagnetic Ground State in the Quantum Spin IceYb2Sn2O7

et al. 2013

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From magnetic, specific heat, 170 Yb Mössbauer effect, neutron diffraction, and muon spin relaxation measurements on polycrystalline Yb 2 Sn 2 O 7 , we show that below the first order transition at 0.15 K all of the Yb 3þ ions are long-range magnetically ordered and each has a moment of 1:1 B which lies at ' 10 to a common fourfold cubic axis. The four sublattice moments have four different directions away from this axis and are therefore noncoplanar. We term this arrangement splayed ferromagnetism. This ground state has a dynamical component with a fluctuation rate in the megahertz range. The net ferromagnetic exchange interaction has an anisotropy that favors the local threefold axis. We discuss our results in terms of the phase diagram proposed by Savary and Balents [Phys. Rev. Lett. 108, 037202 (2012) There is much interest in the pyrochlore lattice compounds R 2 M 2 O 7 , where R is a rare earth and M is a transition or sp metal. The chief motivation is that the R ions form corner-sharing tetrahedra such that the interionic interactions are prone to geometrical frustration. A number of different situations have been encountered depending on the form, sign, size, and anisotropy of the various possible interionic interactions [1]. The quest for the spin liquid state, namely a ground state where the spins are strongly correlated while they show no long-range order and are dynamical, has motivated important theoretical and experimental efforts. For example, pyrochlores like Ho 2 Ti 2 O 7 , where the R ¼ Ho ion has a large axial anisotropy and where there is a net ferromagnetic interaction, evidence magnetic frustration which shows analogies with the positional fluctuations of the protons in ice. Such systems have been labeled ''spin ice '' [2]. Their behavior is essentially driven by the classical dipolar interaction between the spins [3]. More recently, the interest has focused on the quantum spin liquid model where exchange interactions determine the low temperature behavior [4-6] and the possibility has been raised that the pyrochlore Yb 2 Ti 2 O 7 is a physical realization of this model [7][8][9][10]. Even more striking, four phases are predicted from a gauge mean field theory depending on values of the symmetry dictated nearest neighbor Hamiltonian parameters: two Higgs phases either ferromagnetic (FM) or antiferromagnetic (AFM), the quantum spin liquid phase, and a new exotic phase, the Coulombic ferromagnetic (CFM) phase [7]. Three types of magnetic excitations which are either gapped or not can be observed: they are respectively associated with an effective electric charge (gapped), an effective magnetic charge (gapped), and an artificial photon (gapless) [9]. Fractional spin excitations are present in the CFM phase.The Higgs FM phase has recently been proposed for Yb 2 Ti 2 O 7 at low temperature [11]. However a longstanding controversy exists as to the intrinsic presence of magnetic Bragg reflections in this compound [11][12][13][14][15][16][17]. In this respect, recent studies show the variability of...

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Section: Prl 110 127207 (2013) P H Y S I C a L R E V I E W L E T T Esupporting

confidence: 80%

Dynamical Splayed Ferromagnetic Ground State in the Quantum Spin IceYb2Sn2O7

et al. 2013

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“…In our case the ratio B meas /B ext depends on B ext which would imply that the applied field affects the system. We note that ∆ 0 /γ µ is reduced compared to the high temperature field width of 80 mT [11] measured above the specific heat anomaly at ≃ 0.25 K. This reduction is consistent with the sporadic nature of the field at the muon. More work is yet needed for an interpretation of the magnitude of this reduction.…”

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Studies of ( and Yb); new results

Réotier

Glazkov

Marı́n

et al. 2006

Physica B: Condensed Matter

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Specific heat and muon spin rotation and relaxation data are presented for two geometrically frustrated systems: Gd 2 Ti 2 O 7 which antiferromagnetically orders and Yb 2 Ti 2 O 7 which presents dynamical short range correlations at low temperature. The muon data help to characterize the spin dynamics of these two compounds.Key words: Magnetism, frustration, pyrochlore.Geometrically derived magnetic frustration arises when the spatial arrangement of the spins is such that it prevents the simultaneous minimization of all interaction energies [1]. Compounds of interest for the investigation of frustration are, for example, the crystallographically ordered pyrochlore structure compounds R 2 Ti 2 O 7 where the rare earth ions (R) form a sub-lattice of corner sharing tetrahedra.We shall focus on two pyrochlore compounds Gd 2 Ti 2 O 7 and Yb 2 Ti 2 O 7 . Reports of experimental data concerning these two systems were already published by some of us, see Refs. [2,3,4,5]. A summary of the muon spin rotation

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“…This is due to a vanishing quadrupolar interaction in the latter compound [22]. 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.…”

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“…[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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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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Spin dynamics in geometrically frustrated compounds

Cited by 28 publications

References 22 publications

Dynamical Splayed Ferromagnetic Ground State in the Quantum Spin IceYb2Sn2O7

Dynamical Splayed Ferromagnetic Ground State in the Quantum Spin IceYb2Sn2O7

Studies of ( and Yb); new results

A novel type of splayed ferromagnetic order observed in Yb₂Ti₂O₇

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Spin dynamics in geometrically frustrated compounds

Cited by 28 publications

References 22 publications

Dynamical Splayed Ferromagnetic Ground State in the Quantum Spin IceYb2Sn2O7

Dynamical Splayed Ferromagnetic Ground State in the Quantum Spin IceYb2Sn2O7

Studies of ( and Yb); new results

A novel type of splayed ferromagnetic order observed in Yb2Ti2O7

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A novel type of splayed ferromagnetic order observed in Yb₂Ti₂O₇