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Pyrochlore magnets of the form 𝑅₂𝐵₂O₇, in which rare-earth ions on the 𝑅 site form a three-dimensional network of corner-sharing tetrahedra, provide a canonical setting for geometrical frustration. Ho-based pyrochlores host a dipolar spin-ice ground state, characterized by Ising moments constrained by the ice rules and elementary excitations analogous to magnetic monopoles. Here we examine how controlled chemical disorder influences this state by introducing site mixing on the nonmagnetic 𝐵 site in two compounds. Ho₂GaSbO₇ contains only Ga³⁺/Sb⁵⁺ charge disorder, whereas Ho₂ScSbO₇ exhibits both charge and substantial size disorder arising from the large ionic-radius mismatch between Sc³⁺ and Sb⁵⁺. Although both materials retain the pyrochlore structure, neutron-scattering measurements reveal a reduced correlation length for the 𝑅/𝐵-site cation ordering and enhanced local structural distortions in Ho₂ScSbO₇. Despite these structural differences, bulk thermodynamic measurements and magnetic diffuse scattering demonstrate that both systems exhibit the defining signatures of a dipolar spin-ice state. Low-energy inelastic neutron spectroscopy further uncovers broad magnetic excitations that develop within the dipolar spin-ice regime, a feature absent in pristine Ho pyrochlores and indicative of disorder-induced splitting of the non-Kramers ground-state doublet. Together, these results show that controlled disorder generates tunable transverse-field-driven quantum fluctuations in Ho-based pyrochlores, although the dipolar spin-ice state is remarkably robust to this disorder.

The quantum dimer magnet, with antiferromagnetic intradimer and interdimer Heisenberg exchange between spin-1/2 moments, is known to host an $$(\left|\uparrow \downarrow \right\rangle -\left|\downarrow \uparrow \right\rangle )/\sqrt{2}$$singlet ground state when the intradimer exchange is dominant. Rare-earth-based quantum dimer systems with strong spin-orbit coupling offer the opportunity for tuning their magnetic properties by using magnetic anisotropy as a control knob. Here, we present bulk characterization and neutron scattering measurements of the quantum dimer magnet Yb2Be2SiO7. We find that the Yb3+ ions can be described by an effective spin-1/2 model at low temperatures and the system does not show signs of magnetic order down to 50 mK. The magnetization, heat capacity, and neutron spectroscopy data can be well-described by an isolated dimer model with highly anisotropic exchange that stabilizes a singlet ground state with a wavefunction $$(\left|\uparrow \uparrow \right\rangle -\left|\downarrow \downarrow \right\rangle )/\sqrt{2}$$or $$(\left|\uparrow \uparrow \right\rangle+\left|\downarrow \downarrow \right\rangle )/\sqrt{2}$$. Our results show that strong spin-orbit coupling can induce unusual entangled states of matter in quantum dimer magnets.

Metallic delafossite oxides are of exceptional interest due to their ultraclean metallic transport. In the case of PdCrO₂, this arises in a triangular-lattice antiferromagnet, creating a unique opportunity to study frustrated magnetism in a very clean metal. Here, we combine a chemical vapor transport crystal growth approach with magnetic, thermodynamic, magnetotransport, and neutron scattering measurements to elucidate the striking anomalous Hall effect (AHE) in antiferromagnetic PdCrO₂. The unconventional AHE (with anomalous Hall conductivity ~10⁵ Ω⁻¹cm⁻¹) and a large positive magnetoresistance effect (>1,000%) are shown to exhibit complex temperature dependencies, persisting to almost seven times the Néel temperature (~250 K). These effects are directly compared to elastic neutron scattering, inelastic neutron scattering, and neutron magnetic pair distribution function data, establishing unambiguous links between anomalous magnetotransport properties and directly probed short-range spin fluctuations. The latter occur over a notably broad temperature range due to geometrical magnetic frustration. Connecting to recent experimental and theoretical developments, these findings are discussed in terms of a temperature-dependent interplay between chiral spin order and chiral spin fluctuations, significantly elucidating the high-temperature anomalous magnetotransport in such compounds.

We present a combined magnetometry, muon spin-relaxation (𝜇⁢SR), and neutron-scattering study of the insulating spin glass Zn_0.5Mn_0.5Te, for which magnetic Mn²⁺ and nonmagnetic Zn2+ ions are randomly distributed on a face-centered cubic lattice. The magnetometry and 𝜇SR results confirm a spin freezing transition around 𝑇𝑓≈23 K, with the spin-fluctuation rate decreasing gradually and somewhat inhomogeneously through the sample volume as the temperature decreases toward 𝑇𝑓. Characteristic spin-correlation times well above 𝑇𝑓 are on the order of 10−10 s, much slower than typically observed in canonical spin glasses but in line with expectations for a cluster spin glass. Using magnetic pair distribution function (mPDF) analysis and reverse Monte Carlo (RMC) modeling of the magnetic diffuse neutron-scattering data, we show that the spin-glass ground state consists of clusters of spins exhibiting short-range-ordered type-III antiferromagnetic correlations with a locally ordered moment of 3.1(1)𝜇_B between nearest-neighbor spins. The type-III correlations decay exponentially as a function of spin separation distance with a correlation length of approximately 5 Å. The diffuse magnetic scattering and corresponding mPDF show no significant changes across 𝑇𝑓, indicating that the dynamically fluctuating short-range spin correlations in the paramagnetic state retain the same basic type-III configuration that characterizes the spin-glass state; the only change apparent from the neutron-scattering data is a gradual reduction of the correlation length and locally ordered moment with increasing temperature. Taken together, these results paint a unique and detailed picture of the local magnetic structure and dynamics in Zn_0.5Mn_0.5Te and provide strong evidence that this material is best described as a cluster spin glass. In addition, this work showcases a statistical method for extracting diffuse scattering signals from neutron powder diffraction data, which we developed to facilitate the mPDF and RMC analysis of the neutron data. This method has the potential to be broadly useful for neutron powder diffraction experiments on a variety of materials with short-range atomic or magnetic order.

We provide experimental evidence for the absence of a magnetic moment in bulk RuO₂, a candidate altermagnetic material, by using a combination of Mössbauer spectroscopy, nuclear forward scattering, inelastic X-ray and neutron scattering, and density functional theory calculations. Using complementary Mössbauer and nuclear forward scattering, we determine the Ru magnetic hyperfine splitting to be negligible. Inelastic X-ray and neutron scattering-derived lattice dynamics of RuO₂ are compared to density functional theory calculations of varying flavors. Comparisons among theory with experiments indicate that electronic correlations, rather than magnetic order, are key in describing the lattice dynamics.