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Abstract:

${\text{YbZn}}_2{\mathrm{GaO}}_5$ is a promising candidate for realizing a quantum spin liquid (QSL) state, particularly owing to its lack of significant site disorder. Pulsed-field magnetometry at 0.5 K shows magnetization saturating near 15 T, with a corrected saturation moment of $2.1(1){\mu }_{\mathrm{B}}$ after subtracting the van Vleck contribution. Our zero-field $\mathrm{\mu }\mathrm{SR}$ measurements down to milliKelvin temperatures provide evidence for a dynamic ground state and the absence of magnetic order. To probe fluctuations in the local magnetic field at the muon site, we performed longitudinal field $\mathrm{\mu }\mathrm{SR}$ experiments. These results provide evidence for spin dynamics with a field dependence that is consistent with a U1A01 Dirac quantum spin liquid as a plausible description of the ground state.

Abstract:

Ruddlesden-Popper oxide phases in the LaxSr2−xCo0.5Ir0.5O4 (0 < x < 1) solid solution can be converted to the corresponding LaxSr2−xCo0.5Ir0.5O4−yHy oxyhydride phases, by topochemical reaction with LiH, in which the hydride ions are substituted exclusively onto the equatorial anion sites of the host framework. Analysis reveals that oxyhydride phases in the range 0.5 < x < 1 adopt LaxSr2−xCo0.5Ir0.5O2+xH2−x compositions which maintain a constant Co1+, Ir3+ oxidation-state combination (confirmed by Co K-edge XANES data), with the presence of low-spin d6 Ir3+ being consistent with the covalent stabilization of the metastable oxyhydride phases via strong Ir–H σ-bonds. Phases at the lanthanum-poor end of the solid solution (x < 0.5) adopt LaxSr2−xCo0.5Ir0.5O4−yHy compositions with lower hydride concentrations (y < 1.5). Magnetisation and μSR data indicate that all the LaxSr2−xCo0.5Ir0.5O4−yHy oxyhydride phases exhibit strong magnetic frustration, attributed to the large-scale cation and anion disorder, and resulting in glassy magnetic behaviour at low temperature.

Abstract:

Muon spectroscopy has become a leading tool for the investigation of local magnetic fields in condensed matter physics, finding applications in the study of superconductivity, magnetism, ionic diffusion in battery materials, and numerous other fields. Though the muon yields quantitative information about the material, this can only be fully interpreted if the nature of the muon site and its stability is fully understood. Electronic structure calculations are of paramount importance for providing this understanding, particularly through a group of techniques that has become known as DFT +μ, density functional theory including the presence of the implanted muon. We describe how these electronic structure calculations can be used to underpin muon spectroscopy, and some examples of the science that follows from this, as well as some of the available software tools that are currently being developed.

Abstract:

Centrosymmetric GdRu2⁢Si2 exhibits a variety of multi-𝑄 magnetic states as a function of temperature and applied magnetic field, including a square skyrmion-lattice phase. The material's behavior is strongly dependent on the direction of the applied field, with different phase diagrams resulting for fields applied parallel or perpendicular to the crystallographic 𝑐 axis. Here, we present the results of muon-spin relaxation (𝜇+⁢SR) measurements on single crystals of GdRu2⁢Si2. Our analysis is based on the computation of muon stopping sites and consideration of quantum zero-point motion effects of muons, allowing direct comparison with the underlying spin textures in the material. The muon site is confirmed experimentally, using angle-dependent measurements of the muon Knight shift. Using transverse-field 𝜇+⁢SR with fields applied along either the [001] or [100] crystallographic directions, we distinguish between the magnetic phases in this system via their distinct muon response, providing additional evidence for the skyrmion and meron-lattice phases, while also suggesting the existence of RKKY-driven muon hyperfine coupling. Zero-field 𝜇+⁢SR provides clear evidence for a transition between two distinct magnetically ordered phases at 39 K.