Intermediate magnetization state and competing orders in Dy2Ti2O7 and Ho2Ti2O7

Abstract

Among the frustrated magnetic materials, spin-ice stands out as a particularly interesting system. Residual entropy, freezing and glassiness, Kasteleyn transitions and fractionalization of excitations in three dimensions all stem from a simple classical Hamiltonian. But is the usual spin-ice Hamiltonian a correct description of the experimental systems? Here we address this issue by measuring magnetic susceptibility in the two most studied spin-ice compounds, Dy2Ti2O7 and Ho2Ti2O7, using a vector magnet. Using these results, and guided by a theoretical analysis of possible distortions to the pyrochlore lattice, we construct an effective Hamiltonian and explore it using Monte Carlo simulations. We show how this Hamiltonian reproduces the experimental results, including the formation of a phase of intermediate polarization, and gives important information about the possible ground state of real spin-ice systems. Our work suggests an unusual situation in which distortions might contribute to the preservation rather than relief of the effects of frustration.

Magnetoelastically induced vibronic bound state in the spin-ice pyrochlore Ho2Ti2O7

“…However, in the case of Tb 2 Ti 2 O 7 , where the coupling occurs at 1 meV, a quantitative description has not yet been achieved due to the complex influence of exchange interactions. Magneto-elastic coupling has also been investigated in the context of spin ice, where the monopole dynamics has been shown to depend on the spin-lattice interaction [40,46,47]. Considering the body of work including our new findings, it is clear that magneto-elastic coupling is an important interaction in the rare-earth pyrochlores and that it will play a major role in the discovery of new quantum phenomena.…”

Machine-learning-assisted insight into spin ice Dy2Ti2O7

“…In going from (a) to (b), the autoencoder has filtered out experimental artifacts such as the red peaks, the missing data at the dark patches, etc. Using both scattering and heat capacity data, we determine the optimal spin Hamiltonian couplings to be = 0.00 (5) K, = 0.005(10) K and = 0.048(3) K with = 1.705 K and = 1.3224 K having been fixed in prior work [17]. identify the optimal Hamiltonian model (magenta cross).…”

“…Spin dynamics occurs through millisecond quantum tunneling processes [11] and the measured characteristic equilibration time τ increases drastically leading to irreversible behavior below 600 mK [12,13,14,15]. This slowdown has resulted in major difficulties [16,17] in measuring and interpreting experiments such as heat capacity at low temperatures.…”

“…There is also a dipolar interaction with strength , which couples the and the spins, according to their displacement vector . Prior work has determined = 1.3224 K and = 1.705 K to high accuracy [17,18,19,20,21]. In the present modeling effort, we seek to determine the three unknown parameters , , and without any use of prior knowledge.…”

Integration of Machine Learning with Neutron Scattering: Hamiltonian Tuning in Spin Ice with Pressure

“…Fig. 1 a), and a magnetic dipolar interaction term, D 15,16 . Previously we have demonstrated the application of nonlinear autoencoders (NLAEs) to analyze neutron diffuse scattering, and used it to autonomously analyze and interpret the ambient pressure measurements on DTO 4,5 .…”