Common glass-forming spin-liquid state in the pyrochlore magnets Dy2Ti2O7 and Ho2Ti<

Abstract

Despite a well-ordered pyrochlore crystal structure and strong magnetic interactions between the Dy 3+ or Ho 3+ ions, no long range magnetic order has been detected in the pyrochlore titanates Ho2Ti2O7 and Dy2Ti2O7. To explore the actual magnetic phase formed by cooling these materials, we measure their magnetization dynamics using toroidal, boundary-free magnetization transport techniques. We find that the dynamical magnetic susceptibility of both compounds has the same distinctive phenomenology, that is indistinguishable in form from that of the dielectric permittivity of dipolar glass-forming liquids. Moreover, Ho2Ti2O7 and Dy2Ti2O7 both exhibit microscopic magnetic relaxation times that increase along the super-Arrhenius trajectories analogous to those observed in glass-forming dipolar liquids. Thus, upon cooling below about 2K, Dy2Ti2O7 and Ho2Ti2O7 both appear to enter the same magnetic state exhibiting the characteristics of a glass-forming spin-liquid. PACS numbers: 75.50.Lk, 75.47.LxA recent proposal 29 that the magnetic state of arXiv:1707.09014v3 [cond-mat.str-el]

Magnetic monopole noise

“…These clearly follow a quantitatively equivalent trajectory to the ac susceptibility -( ) of Ref. 25,35 and thus correspond well with the -( ) derived from numerous susceptibility studies of this material (Refs. 22,23,24,25).…”

“…It has been established empirically that the susceptibility-derived time constants -( ) representing the magnetization dynamics of Dy2Ti2O7 diverge with decreasing T (Refs 22,23,24) and are likely heterogeneous 25,35 . This type of ac susceptibility measurement has been made for Dy2Ti2O7 in different sample shapes ranging from polycrystalline samples 24 to toroidal single crystals 25,35 In E.D. Fig.…”

“…Additionally, evidence for a heterogeneous distribution of microscopic spin relaxation rates contributing to -( ) had been adduced from the stretched-exponential form for the time dependence of magnetization 25,35 in Dy2Ti2O7. From consideration of the related ac susceptibility studies [22][23][24][25]35 and the similarity between -( ) and ( ) , we estimate that any effects of such heterogeneity on the flux-noise spectrum S ¥ (ω, T) would first become visible at temperatures below T=1K. Therefore, they are unlikely to have been detected in these first SNS studies.…”

Frustrated two dimensional quantum magnets

“…It is also expected from simulations that the residual entropy in pyrochlore and 2D kagome spin ice is removed by ordering at a temperature scale which is lower by about an order of magnitude compared to the dipolar spin-flip scale where the spin-ice state forms [37]. The order is characterized by a staggered structure of 2-in, 2-out and 2-out, 2-in tetrahedrons or it may be a dipolar spin glass state [44]. Spin models may also exhibit continuous accidental degeneracies for specific model parameters which are larger than requested by the global symmetries of the Hamiltonian.…”

“…We assume a spinflop phase, i. e. magnetic ordering in the xy plane with ordering vector Q, and a uniform magnetic field defining the z direction, and omit the incoherent part in Eq. (44). The cross-section of coherent magnetic diffraction of a magnetically ordered system in a uniform applied magnetic field, ignoring the Debye-Waller-Factor is evaluated as 5…”