Spin dynamics in highly frustrated pyrochlore magnets

Abstract

Abstract. This paper aims at showing the complementarity between time-of-flight and triple-axis neutron scattering experiments, on the basis of two topical examples in the field of geometrical magnetic frustration. Rare earth pyrochlore magnets R 2 Ti 2 O 7 (R is a rare earth) play a prominent role in this field, as they form model systems showing a rich variety of ground states, depending on the balance between dipolar, exchange interactions and crystal field. We first review the case of the XY antiferromagnet Er 2 Ti 2 O 7 . Here a transition towards a Néel state is observed, possibly induced by an order-bydisorder mechanism. Effective exchange parameters can be extracted from S(Q, ω). We then examine the case of the spin liquid Tb 2 Ti 2 O 7 . Recent experiments reveal a complex ground state characterized by "pinch points" and supporting a low energy excitation. These studies demonstrate the existence of a coupling between crystal field transitions and a transverse acoustic phonon mode.

Thermodynamic properties of quadrupolar states in the frustrated pyrochlore magnet Tb2Ti2O7

“…It is thus apparently different from the magnetic dipole order inferred by earlier theories [7,8]. This mysterious, or hidden, order is an important subject for the study of the actual nature of the ground state of Tb 2 Ti 2 O 7 [9][10][11][12][13][14][15][16][17][18].…”

Quadrupole Order in the Frustrated PyrochloreTb2+xTi2−xOTakatsu1, Onoda2, Kittaka3 et al. 2016Phys. Rev. Lett.58158901View full textAdd to dashboardCite

“…interactions between magnetic dipole moments [the first three terms of Eq. (1)] and the perturbation through first excited crystal-field (CF) states [14,32], and by taking another assumption of Jahn-Teller (JT) distortion [28,33]. Under the present postulation, two ground states of off-stoichiometric Tb 2+x Ti 2−x O 7+y samples [34] will possibly be accounted for by the U(1) QSL (x < x c ) and electric quadrupolar (x > x c ) states of Ref.…”

“…However, the origin of this spin liquid state of TTO has been elusive for more than a decade despite many investigations (see Refs. [4,13,28] and references therein, and recent Refs. [29-31]), and is still under hot debate [13,28].…”

“…[4,13,28] and references therein, and recent Refs. [29-31]), and is still under hot debate [13,28]. To solve this challenging problem of TTO, we start this investigation by postulating that the theoretically-proposed interaction between electric quadrupole moments of non-Kramers ions including Tb 3+ [the fourth term of Eq.…”

Magnetisation Processes in Geometrically Frustrated Spin Networks with Self-Assembled Cliques

“…A typical example is the case of Ising spins s = ±1 on a triangular lattice when the combination of ferromagnetic/antiferromagnetic interactions J ij = ±1 gives the product J ij J jk J ki < 0 along the triangle edges. In a more complex lattice geometry, different patterns of antiferromagnetic ordering take part, leading to the residual entropy [38] and a sequence of fractional magnetisation plateaus on the hysteresis loop in Ising-type [39][40][41] and XY-antiferromagnetic [42] systems.…”