Electrical Noise From Phase Separation In Pr2/3Ca1/3MnO3 Single Crystal

Low frequency electrical noise measurements have been used to probe the electronic state of the perovskite-type manganese oxide Pr2/3Ca1/3MnO3 versus temperature and in the vicinity of the field-induced transition from the insulating, charge-ordered state (I-CO) to the metallic, ferromagnetic state (M-F). At high temperature we have observed a high level of the excess noise with mainly a gaussian distribution of the resistance fluctuations, and the associated power spectral density has a standard 1/f dependence. However, in the hysteretic region, where the electrical resistance depends dramatically on the sample history, we have observed a huge non-gaussian noise characterized by two level fluctuator-like switching (TLS) in the time domain. We discuss the origin of the noise in terms of percolative behavior of the conductivity. We speculate that the dominant fluctuators are manganese clusters switching between the M-F and the I-CO phases.Comment: RevTeX, 6 pages with 3 figure

Lattice and spin excitations in multiferroic h-YMnO3

We used Raman and terahertz spectroscopies to investigate lattice and magnetic excitations and their cross-coupling in the hexagonal YMnO3 multiferroic. Two phonon modes are strongly affected by the magnetic order. Magnon excitations have been identified thanks to comparison with neutron measurements and spin wave calculations but no electromagnon has been observed. In addition, we evidenced two additional Raman active peaks. We have compared this observation with the anti-crossing between magnon and acoustic phonon branches measured by neutron. These optical measurements underly the unusual strong spin-phonon coupling