8 Search Results

While the spin-ice state of bulk pyrochlores such as Dy_2⁢Ti₂⁢O₇ and Ho_2⁢Ti₂⁢O₇ has been extensively studied in the past several decades due to its unique degenerate ground state and emergent monopole excitation, whether it survives in the thin-film form remains a mystery. The limited volume of the thin-film sample makes it challenging to study the intrinsic magnetic properties. Here, we synthesized 18-nm-thick Dy_2⁢Ti₂⁢O₇ thin film on yttria-stabilized zirconia with 9.5 mol% Y₂⁢O₃ substrate and capped it by a thin conductive Bi₂⁢Ir₂⁢O₇ layer and performed the proximitized magnetoresistance measurements. Our Letter found that the ice-rule-breaking phase transition survives but with amore » modified effective nearest-neighbor interaction (𝐽_eff=1.054 K) and distorted Ising spin axes (𝜀 = +0.051) compared to the bulk crystal. Furthermore, the results are supported by the simultaneously measured capacitive torque magnetometry. Our Letter demonstrates that proximitized transport is an effective tool for thin films of insulating frustrated magnets.« less

Chemical transformations on catalyst surfaces occur through series and parallel reaction pathways. These complex networks and their behavior can be most simply evaluated through a three-species surface reaction loop (A* to B* to C* to A*) that is internal to the overall chemical reaction. Application of an oscillating dynamic catalyst to this reactive loop has been shown to exhibit one of three types of behavior: (1) a positive net flux of molecules about the loop in the clockwise direction, (2) a negative net flux of molecules about the loop in the counterclockwise direction, or (3) negligible flux of molecules aboutmore » the loop at the limit cycle of reaction. Three-species surface loops were simulated with microkinetic modeling to assess the reaction loop behavior resulting from a catalytic surface oscillating between two or more catalyst surface energy states. Selected input parameters for the simulations spanned an 11-dimensional parameter space using 127 688 different parameter combinations. Their converged limit cycle solutions were analyzed for their loop turnover frequencies, the majority of which were found to be approximately zero. Classification and regression machine learning models were trained to predict the sign and magnitude of the loop turnover frequency and successfully performed above accessible baselines. Notably, the classification models exhibited a baseline weighted F1 score of 0.49, whereas trained models achieved weighted F1 scores of 0.94 and 0.96 when trained on the parameters used to define the simulations and derived rate constants, respectively. The trained models successfully predicted catalytic loop behavior, and interpretation of these models revealed all input parameters to be important for the prediction and performance of each model.« less

Abstract While geometrically frustrated quantum magnets host rich exotic spin states with potentials for revolutionary quantum technologies, most of them are necessarily good insulators which are difficult to be integrated with modern electrical circuit. The grand challenge is to electrically detect the emergent fluctuations and excitations by introducing charge carriers that interact with the localized spins without destroying their collective spin states. Here, we show that, by designing a Bi ₂ Ir ₂ O ₇ /Dy ₂ Ti ₂ O ₇ heterostructure, the breaking of the spin-ice rule in insulating Dy ₂ Ti ₂ O ₇ leads to a chargemore » response in the conducting Bi ₂ Ir ₂ O ₇ measured as anomalous magnetoresistance during the field-induced Kagome ice-to-saturated ice transition. The magnetoresistive anomaly also captures the characteristic angular and temperature dependence of this ice-rule-breaking transition, which has been understood as magnetic monopole condensation. These results demonstrate a novel heteroepitaxial approach for electronically probing the transition between exotic insulating spin states, laying out a blueprint for the metallization of frustrated quantum magnets.« less

We report understanding the effects of the interfacial modification to the functional properties of magnetic topological insulator thin films is crucial for developing novel technological applications from spintronics to quantum computing. Here, a large electronic and magnetic response is reported to be induced in the intrinsic magnetic topological insulator MnBi₂Te₄ by controlling the propagation of surface oxidation. It is shown that the formation of the surface oxide layer is confined to the top 1–2 unit cells but drives large changes in the overall magnetic response. Specifically, a dramatic reversal of the sign of the anomalous Hall effect is observed tomore » be driven by finite thickness magnetism, which indicates that the film splits into distinct magnetic layers each with a unique electronic signature. These data reveal a delicate dependence of the overall magnetic and electronic response of MnBi₂Te₄ on the stoichiometry of the top layers. This study suggests that perturbations resulting from surface oxidation may play a non-trivial role in the stabilization of the quantum anomalous Hall effect in this system and that understanding targeted modifications to the surface may open new routes for engineering novel topological and magnetic responses in this fascinating material.« less

Effective nonmagnetic control of the spin structure is at the forefront of the study for functional quantum materials. This study demonstrates that, by applying an anisotropic strain up to only 0.05%, the metamagnetic transition field of spin–orbit-coupled Mott insulator Sr₂IrO₄ can be in situ modulated by almost 300%. Simultaneous measurements of resonant X-ray scattering and transport reveal that this drastic response originates from the complete strain-tuning of the transition between the spin-flop and spin-flip limits, and is always accompanied by large elastoconductance and magnetoconductance. This enables electrically controllable and electronically detectable metamagnetic switching, despite the antiferromagnetic insulating state. The obtainedmore » strain-magnetic field phase diagram reveals that C₄-symmetry-breaking anisotropy is introduced by strain via pseudospin-lattice coupling, directly demonstrating the pseudo-Jahn–Teller effect of spin–orbit-coupled complex oxides. The extracted coupling strength is much weaker than the superexchange interactions, yet crucial for the spontaneous symmetry-breaking, affording the remarkably efficient strain-control.« less

Ruddlesden-Popper type Sr_n+1Ir_nO_3n+1 compounds are a major focus of condensed matter physics, where the subtle balance between electron-electron correlation, spin–orbit interaction, and crystal field effect brings a host of emergent phenomena. While it is understandable that a canted antiferromagnetic insulating state with an easy-plane anisotropy is developed in Sr₂IrO₄ as the two-dimensional limit of the series, it is intriguing that bilayer Sr₃Ir₂O₇, with slightly higher effective dimensionality, stabilizes c-axis collinear antiferromagnetism. This also renders Sr₃Ir₂O₇ a unique playground to study exotic physics near a critical spin transition point. However, the epitaxial growth of Sr₃Ir₂O₇ is still a challenging task becausemore » of the narrow growth window. In our research, we have studied the thermodynamic process during the synthesis of Sr₃Ir₂O₇ thin films. We expanded the synthesis window by mapping out the relationship between the thin film crystal structure and the gas pressure. Furthermore, our work thus provides a more accessible avenue to stabilize metastable materials.« less

We report the observation of a linear magnetoresistance in single crystals and epitaxial thin films of the pyrochlore iridate Bi₂Ir₂O₇. The linear magnetoresistance is positive and isotropic at low temperatures, without any sign of saturation up to 35 T. As temperature increases, the linear field dependence gradually evolves to a quadratic field dependence. The temperature and field dependence of magnetoresistance of Bi₂Ir₂O₇ bears strikingly resemblance to the scale invariant magnetoresistance observed in the strange metal phase in high Tc cuprates. However, the residual resistivity of Bi₂Ir₂O₇ is more than two orders of magnitude higher than the curpates. Our results suggestmore » that the correlation between linear magnetoresistance and quantum fluctuations may exist beyond high temperature superconductors.« less