S. N. Gvasaliya

Quantum magnets under pressure: controlling elementary excitations in TlCuCl3.

We follow the evolution of the elementary excitations of the quantum antiferromagnet TlCuCl3 through the pressure-induced quantum critical point, which separates a dimer-based quantum disordered phase from a phase of long-ranged magnetic order. We demonstrate by neutron spectroscopy the continuous emergence in the weakly ordered state of a low-lying but massive excitation corresponding to longitudinal fluctuations of the magnetic moment. This mode is not present in a classical description of ordered magnets, but is a direct consequence of the quantum critical point.

Tuning the superconducting and magnetic properties of Fe y Se 0.25 Te 0.75 by varying the iron content

The superconducting and magnetic properties of FeySe0.25Te0.75 single crystals (0.9≤y≤1.1) were studied by means of x-ray diffraction, superconducting quantum interference device magnetometry, muon-spin rotation, and elastic neutron diffraction. The samples with y<1 exhibit coexistence of bulk superconductivity and incommensurate magnetism. The magnetic order remains incommensurate for y≥1 but with increasing Fe content superconductivity is suppressed and the magnetic correlation length increases. The results show that the superconducting and the magnetic properties of the FeySe1−xTex can be tuned not only by varying the Se/Te ratio but also by changing the Fe content. ©2010 The American Physical Society

Spin-glass state and long-range magnetic order in Pb ( Fe 1 / 2 Nb 1 / 2 ) O 3 seen via neutron scattering and muon spin rotation

We have investigated the magnetic ground state of the multiferroic relaxor ferroelectric

Quasi-Elastic Scattering, Random Fields and phonon-coupling effects in PbMg1/3Nb2/3O3

\text{Pb}({\text{Fe}}_{1/2}{\text{Nb}}_{1/2}){\text{O}}_{3}

Disorder and relaxation mode in the lattice dynamics of PbMg

with

_{1/3}

\ensuremath{\mu}\text{SR}

Nb

spectroscopy and neutron scattering. We find that a transition to a partially disordered phase occurs below

_{2/3}

T=20\text{ }\text{K}

O

that coexists with long-range antiferromagnetic ordering. The disordered phase resembles a spin glass. No clustering of magnetic ions could be evidenced by

_3

\ensuremath{\mu}\text{SR}