Meyer-Neldel rule in the conductivity of manganite single crystals

The Meyer-Neldel behavior of conductivity of low-doped manganite ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_{\mathit{x}}{\mathrm{MnO}}_3$ single crystals has been investigated. The evolution of the isokinetic temperature of conductivity, modified by Ca-doping, hydrostatic pressure, and current bias has been determined. In addition, the evolution of isokinetic temperature with ageing has also been studied. The Meyer-Neldel behavior of the manganite system stems from the multiexcitation entropy mechanism. The isokinetic temperature turned out to be a sensitive parameter characterizing changes in the transport properties of mixed valence manganites, which in the presence of a detailed theoretical model of the excitations coupling in manganites could become a powerful tool for the characterization and investigation of transport properties of manganites.

Figure 1

Temperature dependence of the resistivity of ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_{\mathit{x}}{\mathrm{MnO}}_3$ single crystals with doping level $x=0.3$, 0.22, 0.2, 0.18, and 0.14 in high (HRS) and low (LRS) metastable resistivity state.

Figure 2

Dependence of the Arrhenius pre-exponential resistivity factor on the local activation energy for various doping levels. Different symbols refer to different temperature ranges in which Eq. (1) was fitted to $\rho \left(T\right)$ data, see the legend. Two resistivity states, HRS- high-resistivity and LRS-low-resistivity metastable states are shown for $x=0.14$.

Figure 3

Dependence of the Arrhenius pre-exponential resisitivty factor on activation energy, obtained using Efros-Shklovskii‘s (a) and Mott‘s (b) law.

Figure 4

Temperature dependence of the resistivity of ${\mathrm{La}}_{0.82}{\mathrm{Ca}}_{0.18}{\mathrm{MnO}}_3$ single crystal at different applied hydrostatic pressures.

Figure 5

Dependence of the Arrhenius resistivity pre-exponential factor on the activation energy for data from Fig. 4 at temperatures above (squares) and below $T_C$ (circles).

Figure 6

Local activation energy of ${\mathrm{La}}_{0.82}{\mathrm{Ca}}_{0.18}{\mathrm{MnO}}_3$ single crystal as a function of temperature at various pressures. Arrows indicate the direction of growing pressure.

Figure 7

Temperature dependence of the resistivity of ${\mathrm{La}}_{0.82}{\mathrm{Ca}}_{0.18}{\mathrm{MnO}}_3$ single crystal at different dc bias currents. Arrows indicate the direction of growing current.

Figure 8

Dependence of the Arrhenius pre-exponential resistivity factor on the activation energy for data from Fig. 7.

Figure 9

Apparent activation energy of ${\mathrm{La}}_{0.82}{\mathrm{Ca}}_{0.18}{\mathrm{MnO}}_3$ single crystal as a function of temperature at different currents.

Figure 10

Temperature dependence of resistivity of ${\mathrm{La}}_{0.86}{\mathrm{Ca}}_{0.14}{\mathrm{MnO}}_3$ single crystal at different dc current bias in the low-resistivity state. Arrows indicate the direction of growing bias current.

Figure 11

Dependence of the Arrhenius LRS resistivity pre-exponential factor on the activation energy for data from Fig. 10.

Figure 12

Temperature dependence of the local activation energy at various bias currents for ${\mathrm{La}}_{0.86}{\mathrm{Ca}}_{0.14}{\mathrm{MnO}}_3$ crystal in LRS (dashed lines) and freshly made HRS state (solid lines). Inset: comparison of the local activation energy of the LRS state (dashed lines) with that of the aged HRS state (solid lines). The arrows indicate the direction of current growth.

Figure 13

Temperature dependence of the resistivity of ${\mathrm{La}}_{0.86}{\mathrm{Ca}}_{0.14}{\mathrm{MnO}}_3$ single crystal seen at different dc bias currents in fresh and aged high-resistivity state. Arrows indicate the direction of current growth.

Figure 14

Dependence of the HRS Arrhenius resistivity pre-exponential factor on the activation energy for data from Fig. 13.

Figure 15

Temperature dependence of the local activation energy at various bias currents for $x=0.14$ LCMO sample in fresh HRS and aged HRS state. The arrows indicate the direction of bias current growth.