The anomalous Hall effect (AHE) has emerged as a key indicator of time-reversal symmetry breaking (TRSB) and topological features in electronic band structures. Absent of a magnetic field, the AHE requires spontaneous TRSB but has proven hard to probe due to averaging over domains. The anomalous component of the Hall effect is thus frequently derived from extrapolating the magnetic field dependence of the Hall response. We show that discerning whether the AHE is an intrinsic property of the field-free system becomes intricate in the presence of strong magnetic fluctuations. As a study case, we use the Weyl semimetal PrAlGe, where TRSB can be toggled via a ferromagnetic transition, providing a transparent view of the AHE's topological origin. Through a combination of thermodynamic, transport, and muon spin relaxation measurements, we contrast the behavior below the ferromagnetic transition temperature to that of strong magnetic fluctuations above. Our results on PrAlGe provide general insights into the interpretation of anomalous Hall signals in systems where TRSB is debated, such as families of kagome metals or certain transition metal dichalcogenides.

The ability to efficiently control topological magnetism is crucial for advancing technological applications and deepening our understanding of magnetic systems. Although emerging van der Waals (vdW) multiferroics present a promising frontier for energy-efficient spin manipulation, the control of topological magnetism remains challenging due to its scarcity in multiferroics. Here, we demonstrate that highly tunable merons and antimerons emerge in monolayer multiferroic CuCrP₂S₆ (CCPS). The antiferroelectric-to-ferroelectric (AFE-FE) transition enhances exchange couplings, notably reducing meron density and increasing meron size during cooling. Merons exhibit unique dynamics, characterized by nontrivial attraction and annihilation processes, which generates distinct long-lived spin waves and reduces meron number difference between AFE and FE phases until they vanish. Importantly, ultrafast laser pulses can induce ferroelectricity-tunable merons from a uniform in-plane magnetization, re-leading to a large difference in meron density between the AFE and FE phases. These findings enhance our understanding of topological magnetism and open up exciting avenues for controlling the properties and dynamics of topological states through electrical and optical methods.

Demand for fast-charging lithium-ion batteries (LIBs) has escalated incredibly in the past few years. A conventional method to improve the performance is to chemically partly substitute the transition metal with another to increase its conductivity. In this study, we have chosen to investigate the lithium diffusion in doped anatase (TiO<inf>2</inf>) anodes for high-rate LIBs. Substitutional doping of TiO<inf>2</inf> with the pentavalent Nb has previously been shown to increase the high-rate performances of this anode material dramatically. Despite the conventional belief, we explicitly show that Nb is mobile and diffusing at room temperature, and different diffusion mechanisms are discussed. Diffusing Nb in TiO<inf>2</inf> has staggering implications concerning most chemically substituted LIBs and their performance. While the only mobile ion is typically asserted to be Li, this study clearly shows that the transition metals are also diffusing, together with the Li. This implies that a method that can hinder the diffusion of transition metals will increase the performance of our current LIBs even further.

Kagome lattice decorated with S = 1/2 spins is one of the most discussed ways to realize a quantum spin liquid. However, all previous material realizations of this model have suffered from additional complications, ranging from additional interactions to impurity effects. Recently, a new quantum kagome system has been identified in the form of averievite Cu5-xZnxV2O10(CsCl), featuring a unique double-layer spacing between the kagome planes. Using muon spin spectroscopy we show that only a complete substitution (i.e., x = 2) of interplanar copper ions leads to a quantum-disordered ground state. In contrast, the parent compound (x = 0) exhibits long-range magnetic order, with a phase transition around 24 K. Experiments performed on the partially substituted material (x = 1) show that the transformation proceeds through an intermediate disordered, partially frozen ground state, unaffected by pressures up to 23 kbar. Our study provides a microscopic view of the magnetism of the decoupling of the kagome layers and establishes the averievite as a new material platform for the experimental study of the fully-decoupled kagome layers.

Understanding ion diffusion mechanisms in layered materials is critical for advancing next-generation battery technologies. Using the well-characterized NaxCoO2 (NCO) system as a model platform, we investigated the temperature-dependent diffusion properties across a broad compositional range (x=0.33−0.89) using muon spin relaxation (μ+SR). Unexpected low-temperature internal magnetic field fluctuations were observed, systematically varying with Na content and appearing well before the onset of long-range diffusion. These fluctuations are attributed to phonon-assisted local Na motion, as suggested by a systematic increase in A with x, concurrent with a decreasing activation energy. The diffusion coefficient was calculated based on the crystal structure using a tailored diffusion model accounting for two inequivalent Na sites, yielding values consistent with those found in other layered battery materials. This work highlights the crucial role of phonon-coupled diffusion mechanisms in enabling ion transport at the microscopic scale, providing new insights into ion dynamics in layered solid-state conductors and their relevance to sodium-ion battery technology.

Multi-band Mott insulators with moderate spin-orbit and Hund’s coupling are key reference points for theoretical concept developments of correlated electron systems. The ruthenate Mott insulator Ca2RuO4 has therefore been intensively studied by spectroscopic probes. However, it has been challenging to resolve the fundamental excitations emerging from the hierarchy of electronic energy scales. Here we apply high resolution resonant inelastic x-ray scattering to probe deeper into the low-energy electronic excitations found in Ca2RuO4. In this fashion, we probe a series of spin-orbital excitations. By taking advantage of enhanced energy resolution, we probe a 40 meV mode through the oxygen K-edge. The polarization dependence of this low-energy excitations exposes a distinct orbital nature, originating from the interplay of spin-orbit coupling and octahedral rotations. Additionally, we discuss the role of magnetic correlations to describe the occurrence of excitations with amplitudes which are multiple of a given energy. Such direct determination of relevant electronic energy scales sharpens the target for theory developments of Mott insulators’ orbital degree of freedom.

The assertion of intrinsic material properties based on measured experimental data is being challenged by emerging sample synthesis protocols, which opens new avenues for discovering novel functionalities. In this study, we revisit one of the most widely studied strongly correlated materials of the early 2000s, NaxCoO2 (NCO). Leveraging the sensitivity of muon spin rotation and relaxation (μ+SR) measurements, we discern significant differences between NCO samples synthesized via conventional solid-state reaction (SSR) and our electrochemical reaction (ECR) approach. Contrary to SSR-synthesized Na0.7CoO2, which exhibits a nonmagnetic ground state, our ECR-derived sample showcases an antiferromagnetic (AF) order from x≥0.7, challenging established phase boundaries. We attribute the observed magnetic phenomena in ECR-NCO to long-range order of Na-ions and/or vacancies, as well as the inherent flexibility of the crystal framework. Our study holds implications for tailoring and optimization of next-generation devices based on layered materials.

In this study, we investigate the influence of Cr-Cr distances on the magnetic properties of triangular lattice antiferromagnets through the lens of the recently synthesized Cr compounds LiCrSe2, 2 , LiCrTe2, 2 , and NaCrTe2. 2 . Our comprehensive analysis integrates existing magnetic structure data and new insights from muon spin rotation measurements, revealing a striking mutual influence between strongly correlated electrons and structural degrees of freedom in systems possessing very different magnetic properties despite having the same crystal symmetry. In particular, we delineate how Cr-Cr distances specifically dictate the magnetic behaviors of the triangular lattice antiferromagnets LiCrSe2, 2 , LiCrTe2, 2 , and NaCrTe2. 2 . By crafting phase diagrams based on these distances, we establish a clear correlation between the structural parameters and the magnetic ground states of these materials together with a wide variety of trivalent Cr triangular lattice layered magnets. Our analysis uncovers a transition range for in-plane and out-of-plane Cr-Cr distances that demarcates distinct magnetic behaviors, highlighting the nuanced role of lattice geometry in the spin-lattice interaction and electron correlation dynamics.

The present study investigated the magnetic nature of a solid solution system consisting of EuCo2P2 and CaCo2P2 using a muon spin rotation and relaxation (mu +SR) technique, which is sensitive to local magnetic environments. The former compound EuCo2P2 is known to enter an incommensurate helical antiferromagnetic (AF) phase below 66 K with neutrons, which was confirmed by the present mu +SR. The magnitude of the ordered Eu moments proposed with neutrons was found to be consistent with that estimated by mu +SR. Furthermore, the latter lattice-collapsed tetragonal phase compound CaCo2P2 is known to enter an A-type AF phase below 90 K, and mu +SR measurements on single crystals revealed the presence of a spin reorientation transition at around 40 K, below which the A-type AF order is likely to be completed. Although all Eu1-xCaxCo2P2 compounds were found to enter a magnetic phase at low temperatures regardless of x, a static ordered state was formed only at the vicinity of the two end compounds, i.e., 0 x 0.4 and 0.9 x 1. Instead, a disordered state, i.e., a random spin-glass state, short-range ordered state, or highly fluctuating state was found in the x range between 0.4 and 0.9, even at the lowest measured temperature (2 K). Together with the magnetization data, our findings clarified the magnetic phase diagram of Eu1-xCaxCo2P2, where a ferromagnetic exchange interaction between Co ions through the Eu2+ ion competes with a direct AF interaction among the Co ions, particularly in the x range between 0.57 and 0.9. This competition yielded multiple phases in Eu1-xCaxCo2P2.

Quantum fluctuations in low-dimensional systems and near quantum phase transitions have significant influences on material properties. Yet, it is difficult to experimentally gauge the strength and importance of quantum fluctuations. Here we provide a resonant inelastic x-ray scattering study of magnon excitations in Mott insulating cuprates. From the thin film of SrCuO2, single- and bi-magnon dispersions are derived. Using an effective Heisenberg Hamiltonian generated from the Hubbard model, we show that the single-magnon dispersion is only described satisfactorily when including significant quantum corrections stemming from magnon-magnon interactions. Comparative results on La2CuO4 indicate that quantum fluctuations are much stronger in SrCuO2 suggesting closer proximity to a magnetic quantum critical point. Monte Carlo calculations reveal that other magnetic orders may compete with the antiferromagnetic Néel order as the ground state. Our results indicate that SrCuO2—due to strong quantum fluctuations—is a unique starting point for the exploration of novel magnetic ground states.