Magnon-polaron and Spin-polaron Signatures in the Specific Heat and Electrical Resistivity of $La_{0.6}Y_{0.1}Ca_{0.3}MnO_3$ in Zero Magnetic Field, and the Effect of $Mn-O-Mn$ Bond Environment

摘要

$La_{0.6}Y_{0.1}Ca_{0.3}MnO_{3}$, an $ABO_{3}$ perovskite manganite oxide,exhibits a non trivial behavior in the vicinity of the sharp peak found in theresistivity $\rho$ as a function of temperature $T$ in zero magnetic field. Thevarious features seen on $d\rho/dT$ are discussed in terms of competing phasetransitions. They are related to the $Mn-O-Mn$ bond environment depending onthe content of the $A$ crystallographic site. A Ginzburg-Landau type theory ispresented for incorporating concurrent phase transitions. The specific heat $C$of such a compound is also examined from 50 till 200 K. A log-log analysisindicates different regimes. In the low temperature conducting ferromagneticphase, a collective magnon signature ($C \simeq T^{3/2}$) is found as for whatare called magnon-polaron excitations. A $C \simeq T^{2/3}$ law is found athigh temperature and discussed in terms of the fractal dimension of theconducting network of the weakly conducting (so-called insulating) phase andOrbach estimate of the excitation spectral behaviors. The need of consideringboth independent spin scattering and collective spin scattering is thusemphasized. The report indicates a remarkable agreement for the Fisher-Langerformula, i.e. $C$ $\sim$ $d\rho/dT$ at second order phase transitions. Withinthe Attfield model, we find an inverse square root relationship between thecritical temperature(s) and the total local $Mn-O-Mn$ strain.