・Carrier-doped manganites with perovskite-based structures have renewed the interest of researchers. Although numerous studies were performed a long time ago,the physical properties of these compounds are quite novel even at present. The electrical resistivity r(T) of La1-xSrxMnO3 conspicuously decreases below the ferromagnetic (FM) transition temperature Tc, sometimes displaying a kind of metal-insulator (M-I) transition. This has been explained as being due to the double exchange mechanism between doped carriers and localized Mn spins, resulting in the effective FM interaction between Mn3+ and Mn4+ ion pairs.
・The fundamental properties of this system may be explained by the double exchange mechanism, but dramatic physical properties such as colossal magnetoresistance (CMR) and magnetic field induced structural transition are staged as a result of the competition between various mechanisms, i.e., the antiferromagnetic superexchange, Jahn-Teller effect, structural instability due to ion-radius mismatching, charge-ordering and orbit-ordering besides the double exchange mechanism. However, the most important competition might be that between the electron system (itinerant or localized) and the lattice system.
・We have investigated the phonon transport anomalies (sound velocity v, thermal conductivity k, thermal diffusivity a, thermal dilatation dL/L) associated with the charge-ordering and the magnetic ordering in manganites.
The system in which we have investigated is in the following;
・La1-XAEXMnO3(AE=Ca, Sr, Pb, Ba)
・RE1-XSrXMnO3(RE=Sm, La, Pr, Nd, Gd, Dy)
・Pr1-XCaX(Mn1-ZMZ)O3(M=Cr, Co, Fe, Ni, Ga)
The thermal diffusivity a is given by k/C, the thermal conductivity k divided by the specific heat C. In insulators, in which the heat conduction is entirely due to phonons, a is expressed as a=vl/3=v2t/3 with the phonon velocity v, the phonon mean free path l and the average scattering time t.
(a)Electric Furnaces (~1000℃), (b)Floating Zone Furnace, (c)Electric Furnace (~1800℃)