Synthesis and crystal growth

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.

Abstract:

We have studied the dynamic and static critical behavior of spin glass transition in insulating La0.9Sr0.1CoO3 single crystal by ac susceptibility and dc magnetization measurements in the vicinity of its freezing temperature (Tf). The dynamic scaling analysis of the frequency dependence of ac susceptibility data yields the characteristic time constant τ 0 1.6 (9) × 10 - 12 s, the dynamic critical exponent z ν 9.5 (2), and a frequency dependence factor K Δ T f / T f (Δ log f) 0.017, indicating that the sample enters into a canonical spin-glass phase below Tf 34.8(2) K. The scaling analysis of non-linear magnetization in the vicinity of Tf through the static scaling hypothesis yields critical exponents β 0.89(1) and γ 2.9(1), which match well with that observed for well known three-dimensional (3D) Heisenberg spin glasses. From the longitudinal component of zero-field-cooled and field-cooled magnetization measurement, we have constructed the H-T phase diagram which represents the field evolution of two characteristic temperatures: the upper one, T w (H), indicates the onset of spin freezing in a uniform external field H, while the lower one, T s (H), marks the onset of strong irreversibility of the frozen state. The low field T s (H) follows the critical line suggested by dAlmeida-Thouless model for canonical spin glass, whereas the T w (H) exhibits a re-entrant behavior with a maximum in the T w (H) at a nonzero field above which it follows the Gabay-Toulouse (GT) critical line which is a characteristic of Heisenberg spin glass. The reentrant behavior of the GT line resembles that predicted theoretically for n-component vector spin glasses in the presence of a uniaxial anisotropy field. © 2013 AIP Publishing LLC.