Phase transitions, partial disorder and multi-kstructures in Gd₂Ti₂O₇

Abstract

The geometrically frustrated antiferromagnet Gd2Ti2O7 exhibits magnetic behaviour of such complexity that it poses a challenge to both experiment and theory. Magnetic ordering commences at TN = 1.1 K and there is a further magnetic phase transition at K. Here we use neutron diffraction to definitively establish the nature of the phase transition at and the magnetic structure adopted below this temperature. Between and TN the structure is partly ordered, as previously reported. Below the remaining spins order, but only weakly. The magnetic structure in this temperature range is shown to be a 4-k structure, closely related to the 1-k structure previously suggested. The 4-k and 1-k variants of the structure are distinguished by analysis of the diffuse scattering, which we believe represents a new method of solving the ‘multi-k’ problem of magnetic structure determination.

Evidence for Gapped Spin-Wave Excitations in the FrustratedGd2Sn2O7Pyrochlore Antiferromagnet from Low-Temperature Specific Heat Measurements

“…Examples of observed phenomenology include spin ice [1], spin glass [2,3], and spin liquid [4] behaviors as well as long-range magnetic order [5,6,7,8,9,10,11] and perhaps some novel type of hidden order [12]. A common trend observed in all of these systems is an apparent persistence of spin dynamics down to the lowest temperatures as revealed by muon spin relaxation (µSR) [3,4,7,8,9,11,12] Perhaps what is most perplexing, is that PSDs have been found in pyrochlores, such as Gd 2 Ti 2 O 7 (GTO) [9,11] and Gd 2 Sn 2 O 7 (GSO) [7,8,13], which, according to neutron scattering experiments [6,10], display long-range magnetic order below a critical temperature T c = 0.74 K for GTO [6] and T c = 1.0 K for GSO [10]. This is highly unusual since conventional wisdom suggests that collective magnon-like excitations, hence spin dynamics, should freeze out in the limit of zero temperature.…”

“…As such, these materials display a wide variety of interesting and unusual behaviors. Examples of observed phenomenology include spin ice [1], spin glass [2,3], and spin liquid [4] behaviors as well as long-range magnetic order [5,6,7,8,9,10,11] and perhaps some novel type of hidden order [12]. A common trend observed in all of these systems is an apparent persistence of spin dynamics down to the lowest temperatures as revealed by muon spin relaxation (µSR) [3,4,7,8,9,11,12], Mössbauer spectroscopy [13] and neutron spin echo [1] experiments.…”

“…Perhaps what is most perplexing, is that PSDs have been found in pyrochlores, such as Gd 2 Ti 2 O 7 (GTO) [9,11] and Gd 2 Sn 2 O 7 (GSO) [7,8,13], which, according to neutron scattering experiments [6,10], display long-range magnetic order below a critical temperature T c = 0.74 K for GTO [6] and T c = 1.0 K for GSO [10]. This is highly unusual since conventional wisdom suggests that collective magnon-like excitations, hence spin dynamics, should freeze out in the limit of zero temperature.…”

Controllable chirality-induced geometrical Hall effect in a frustrated highly correlated metal

“…The simulations reproduce the two-phase transitions, with the lower-temperature phase possessing the 4 − q order and the highertemperature phase possessing the 1 − q order (within the framework of these simulations, the transitions at T 2 and T N appear to be first and second order, respectively, which is consistent with experiments; the order of the transitions, however, has not yet been confirmed with complete certainty due to computational limitations). The transition between M2 and M1 is driven by thermal fluctuations favouring the 1 − q state, because the order-by-disorder mechanism stabilizes coplanar magnetic order at finite temperature for a frustrated FCC lattice 25,26 . We note that the analysis of the NMR data in ref.…”

“…However, the 4 − q state is expected to be more energetically favourable than the 1 − q state in Kondo-lattice systems. Indeed, a highly frustrated insulator Gd 2 Ti 2 O 7 has been shown to have a 4 − q ground state and a 1 − q state at higher temperatures 26 . This trend also is consistent with general theoretical arguments that thermal fluctuations tend to stabilize the simpler magnetic configuration 25 .…”