Muons and magnets

Abstract:

An emerging concept for identification of different types of spin liquids [C. Broholm et al., Science 367, eaay0668 (2020)] is through the use of spontaneous spin noise [S. Chatterjee, J. F. Rodriguez-Nieva, E. Demler, Phys. Rev. B 99, 104425 (2019)]. Here, we develop spin noise spectroscopy for spin liquid studies by considering Ca10Cr7O28, a material hypothesized to be either a quantum or a spiral spin liquid (SSL). By enhancing techniques introduced for magnetic monopole noise studies [R. Dusad et al., Nature 571, 234–239 (2019)], we measure the time and temperature dependence of spontaneous flux Φ(t, T) and thus magnetization M(t, T) of Ca10Cr7O28 samples. The resulting power spectral density of magnetization noise SMω, T reveals intense spin fluctuations with SMω, T∝ω-α(T) and 0.84

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.