Dr Dharmalingam Prabhakaran

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.

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.

Abstract:

Neutron time-of-flight spectroscopy has been employed to study the crystal-field splitting of Pr3+ in the pyrochlore stannate Pr 2Sn2O7. The crystal field has been parameterized from a profile fit to the observed neutron spectrum. The single-ion ground state is a well-isolated non-Kramers doublet of Γ3+ symmetry with a large Ising-like anisotropy, χzz/ χ⊥≈60 at 10 K, but with a significant admixture of terms |MJ≠±J, which can give rise to quantum zero-point fluctuations. This magnetic state satisfies the requirements for quantum spin-ice behavior. © 2013 American Physical Society.