Far-from-equilibrium monopole dynamics in spin ice
Nature Physics 10:2 (2014) 135-139
Abstract:
Condensed matter in the low-temperature limit reveals exotic physics associated with unusual orders and excitations, with examples ranging from helium superfluidity to magnetic monopoles in spin ice. The far-from-equilibrium physics of such low-temperature states may be even more exotic, yet to access it in the laboratory remains a challenge. Here we demonstrate a simple and robust technique - the 'magnetothermal avalanche quench' - and its use in the controlled creation of non-equilibrium populations of magnetic monopoles in spin ice at millikelvin temperatures. These populations are found to exhibit spontaneous dynamical effects that typify far-from-equilibrium systems and yet are captured by simple models. Our method thus opens new directions in the study of far-from-equilibrium states in spin ice and other exotic magnets. © 2014 Macmillan Publishers Limited.Circularly polarized x-ray scattering investigation of spin-lattice coupling in TbMnO3 in crossed electric and magnetic fields
Physical Review B - Condensed Matter and Materials Physics 88:21 (2013)
Abstract:
We present a study of the magnetic and crystallographic structure of TbMnO3 in the presence of crossed electric and magnetic fields using circularly polarized x-ray nonresonant scattering. A comprehensive account is presented of the scattering theory and data analysis methods used in our earlier studies, and in addition we present interesting high magnetic field data and its analysis. We discuss in detail how polarization analysis was used to reveal structural information, including the arrangement of Tb moments which we proposed for H=0 T, and how the diffraction data for HTerahertz frequency electromagnon and magnon modes in multiferroic cupric oxide
International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz (2013)
Abstract:
We examined the terahertz magnetoelectric response of cupric oxide, a high-temperature multiferroic with a cycloidal spin structure that induces an electrical polarisation. Terahertz time-domain spectroscopy at various temperatures and magnetic fields uncovered electromagnon and magnon modes, providing insights into the spin Hamiltonian. © 2013 IEEE.Hour-glass magnetic spectrum arising from a striped cluster spin-glass ground state in La1.75 Sr0.25 CoO4
Physical Review B - Condensed Matter and Materials Physics 88:16 (2013)
Abstract:
We report inelastic neutron scattering results that reveal an hour-glass magnetic excitation spectrum in La1.75Sr0.25CoO 4. The magnetic spectrum is similar to that observed previously in La1.67Sr0.33CoO4, but the spectral features are broader. We show that the spectrum of La1.75Sr 0.25CoO4 can be modelled by the spin dynamics of a system with a disordered cluster spin glass ground state. Bulk magnetization measurements are presented that support the proposed glassy ground state. The observations reiterate the importance of quasi-one-dimensional magnetic correlations and disorder for the hour-glass spectrum, and suggest that disordered spin and charge stripes exist at lower doping in La 2-xSrxCoO4 than previously thought. © 2013 American Physical Society.Erratum: Photoinduced melting of the orbital order in La 0.5 Sr1.5 MnO4 measured with 4-fs laser pulses (Physical Review B (2013) 88 (075107) DOI:10.1103/PhysRevB.88.075107)
Physical Review B - Condensed Matter and Materials Physics 88:15 (2013)