Concentration phase diagram of Ba(x)Sr(1-x)TiO3 solid solutions

Method of derivation of phenomenological thermodynamic potential of solid solutions is proposed in which the interaction of the order parameters of constituents is introduced through the account of elastic strain due to misfit of the lattice parameters of the end-members. The validity of the method is demonstrated for Ba(x)Sr(1-x)TiO3 system being a typical example of ferroelectric solid solution. Its phase diagram is determined using experimental data for the coefficients in the phenomenological potentials of SrTiO3 and BaTiO3. In the phase diagram of the Ba(x)Sr(1-x)TiO3 system for small Ba concentration, there are a tricritical point and two multiphase points one of which is associated with up to 6 possible phases.Comment: 8 pages, 3 figure

B-T phase diagram of CoCr2O4 in magnetic fields up to 14 T

We have measured the magnetization and specific heat of multiferroic CoCr2O4 in magnetic fields up to 14 T. The high-field magnetization measurements indicate a new phase transition at T* = 5 - 6 K. The phase between T* and the lock-in transition at 15 K is characterized by magnetic irreversibility. At higher magnetic fields, the irreversibility increases. Specific-heat measurements confirm the transition at T*, and also show irreversible behavior. We construct a field-temperature phase diagram of CoCr2O4.Comment: 4 page

Origin of Low-Energy Excitations in Charge-Ordered Manganites

The low-energy excitations in the charge-ordered phase of polycrystalline La0.25Ca0.75MnO3 are explored by frequency-domain terahertz spectroscopy. In the frequency range from 4 cm^-1 to 700 cm^-1 (energies 0.4 meV to 90 meV) and at temperatures down to 5 K, we do not detect any feature that can be associated with the collective response of the spatially modulated charge continuum. In the antiferromagnetically ordered phase, broad absorption bands appear in the conductivity and permittivity spectra around 30 cm^-1 and 100 cm^-1 which are assigned to former acoustic phonons optically activated due to a fourfold superstructure in the crystal lattice. Our results indicate that characteristic energies of collective excitations of the charge-ordered phase in La0:25Ca0:75MnO3, if any, lie below 1 meV. At our lowest frequencies of only few wavenumbers a strong relaxation is observed above 100 K connected to the formation of the charge-ordered state.Comment: 5 pages, 3 figure