Dynamical Splayed Ferromagnetic Ground State in the Quantum Spin IceYb2Sn2O7

Abstract

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...

Doping-induced quantum crossover in Er2Ti2−xSnxO7

“…We also notice a broad maximum centered just above 1 K, especially pronounced for higher x. A similar feature has been observed in several other pyrochlore systems [16,23,29] and it has been ascribed to exchange splitting of the ground state doublet due to the build up of magnetic correlations at low temperatures [23].…”

“…For Yb compounds, an additional complication arises from a strong sample dependence where a small Yb deficiency [21] or "stuffing" of Yb on the Ti-site [22] in Yb 2 Ti 2 O 7 quickly suppresses a first-order transition around 240 mK. Similarly for Yb 2 Sn 2 O 7 two recent reports have shown a transition to a highly dynamic splayed ferromagnetic structure below 140 mK [23,24]. It has been argued that the system is very susceptible to even the smallest amounts of disorder due to the proximity of a quantum critical point, resulting in a cluster glasslike state [24].…”

XY antiferromagnetic ground state in the effectiveS=12pyrochloreYb2Ge2O7Hallas1, Gaudet2, Wilson3 et al. 2016Phys. Rev. B383350View full textAdd to dashboardCite

“…There are six basis vectors that make up the Γ 9 manifold. Linear combinations of these six basis vectors can give non-collinear ferromagnetic structures related to the spin ice-state, such as the splayed ferromagnetic state found in Yb 2 Sn 2 O 7 [13].…”

“…The crystal electric field states for Yb 2 Ti 2 O 7 are well understood [7][8][9], while those corresponding to Er 2 Ti 2 O 7 are less well-determined [10,11] [8,12,13]. These two materials have also both been found to order into a canted ferromagnetic state at low temperatures [13][14][15][16]. However, there are exotic characteristics to such states, at least in the case of Yb 2 Ti 2 O 7 , for which single crystal studies are required.…”

Phase Competition in the Palmer-Chalker XY Pyrochlore Er2Pt2O<

“…Of these states, all but Γ 7 have been experimentally observed in the XY pyrochlores. This XY family is made up of Yb 2 B 2 O 7 and Er 2 B 2 O 7 with B = Ge, Ti, and Sn, where: (i) The order-by-disorder candidate Er 2 Ti 2 O 7 orders into ψ 2 [17] (ii) Er 2 Ge 2 O 7 and Yb 2 Ge 2 O 7 have as-of-yet unidentified ordered states within Γ 5 (ψ 2 or ψ 3 ) [12,18] and (iii) Both Yb 2 Sn 2 O 7 [19,20] and some samples of Yb 2 Ti 2 O 7 [21][22][23][24][25] order into the Γ 9 splayed ferromagnetic state. This ensemble of magnetic ground states supports the picture of a rich phase space.…”