Spin dynamics in highly frustrated pyrochlore magnets

Sylvain Petit,Solène Guitteny,Pierre Bonville,Jacques Ollivier,Isabelle Mirebeau,Claudia Decorse,Hannu Mutka,Julien Robert

doi:10.1051/epjconf/20158303012

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 Neel state is observed, possibly induced by an order-by-disorder 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.

Highlights

Frustrated magnetism is a forefront research topic within condensed matter physics, as testified by the wealth of exotic phenomena discovered over the past years [1,2,3]
Rare earth pyrochlore magnets R2Ti2O7 (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
Combination of TOF and polarized triple axis measurements demonstrate the existence of a low energy propagating excitation emanating from the spin liquid ground state

Summary

Introduction

Frustrated magnetism is a forefront research topic within condensed matter physics, as testified by the wealth of exotic phenomena discovered over the past years [1,2,3]. Despite the high luminosity of such instruments, the counting time in one configuration (wavelength, magnetic field, temperature) is still of the order of about one day, so that measuring precisely the temperature, field dependence or the spin polarization analysis at a given Q position, remains the preserve of triple axis spectrometers (TAS). The suite of both spectrometers is clearly complementary. Anomalies of the phonon modes, as well as of the first crystal electric field (CEF) level, suggest a strong dynamical coupling to the lattice

Er2Ti2O7

Tb2Ti2O7

Conclusion