Dr Benjamin Huddart

Abstract:

Wepresent the results of muon-spin spectroscopy (μ+SR) measurements on the molecular spin ladder system (Hpip)2CuBr4(1−x)Cl4x, [Hpip = (C5H12N)]. Using transverse field μ+SR we are able to identify characteristic behaviour in each of the regions of the phase diagram of the x = 0 strong-rung spin ladder system (Hpip)2CuBr4. Comparison of our results to those of the dimer-based molecular magnet Cu(pyz)(gly)(ClO4) shows several common features.Welocate the crossovers in partially disordered (Hpip)2CuBr4(1−x)Cl4x (x = 0.05), where a region of behaviour intermediate between quantum disordered and Luttinger liquid-like is identified. Our interpretation of the results incorporates an analysis of the probable muon stopping states in (Hpip)2CuBr4 based on density functional calculations and suggests how the muon plus its local distortion can lead to a local probe unit with good sensitivity to the magnetic state. Using longitudinal field μ+SR we compare the dynamic response of the x = 1 strong-rung material (Hpip)2CuCl4 to that of the strong-leg material (C7H10N)2CuBr4 (known as DIMPY) and demonstrate that our results are in agreement with predictions based on interacting fermionic quasiparticle excitations in these materials.

Abstract:

We present the results of a muon-spin spectroscopy investigation of GaV4S8-ySey with y=0,2,4, and 8. Zero-field measurements suggest that GaV4Se8 and GaV4S8 have distinct magnetic ground states, with the latter material showing an anomalous temperature dependence of the local magnetic field. It is not possible to evolve the magnetic state continuously between these two systems, with the intermediate y=2 and 4 materials showing glassy magnetic behavior at low temperature. The skyrmion lattice (SkL) phase is evident in the y=0 and 8 materials through an enhanced response of the muon-spin relaxation to the emergent dynamics that accompany the SkL. For our polycrystalline samples of GaV4Se8, this enhanced dynamic response is confined to a smaller region of the magnetic field-temperature phase diagram than the previous reports of the SkL in single crystals.