Current localization and Joule self-heating effects in Cr-doped ${\mathrm{Nd}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_3$ manganites

The effects of dc excitation current on the current-voltage curves of polycrystalline samples of ${\mathrm{Nd}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{Mn}}_{0.96}{\mathrm{Cr}}_{0.04}{\mathrm{O}}_3$ were investigated. The experimental results show that an abrupt jump of the voltage is concomitant with a huge increase in the temperature of the sample. A simple model and estimates for Joule self-heating effects support the experimental data. Moreover, the data strongly suggest that both the current localization in the metallic paths and local Joule self-heating effects are essential ingredients to understand the current-induced phase transition in phase-separated manganites.

Figure 1

$V∕I\left(T\right)$ (right axis) and $M\left(T\right)$ (left axis) of ${\mathrm{Nd}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{Mn}}_{0.96}{\mathrm{Cr}}_{0.04}{\mathrm{O}}_3$. The inset displays the copper block sample holder experimental setup. Warming and cooling cycles in $V∕I\left(T\right)$ measurements $(I=0.05\mathrm{mA})$ are indicated by the arrows.

Figure 2

$I\text{−}V$ curve at 50 K (right, open squares) and the corresponding temperature rise of the sample $T_S$ (left, crosses) vs $I$. The inset shows the temperature dependence of $I_L$. Arrows denote increasing and decreasing $I$.

Figure 3

$I\text{−}V$ curves of the Cr-NCMO compound at several temperatures. The inset displays the data in the vicinity of $T_{CO}$. The arrows point to the increasing and decreasing values of $I$.

Figure 4

Temperature rise of the sample $\Delta T=T_S-T$ vs $I$. The copper-block sample holder measuring temperatures $T$ for each $I\text{−}V$ curve are indicated. The inset shows $\Delta T$ close to $T_{CO}$. The arrows point to the increasing and decreasing values of $I$.

Figure 5

The $I$ vs $\Delta T$ curve at 30 K (open squares) and the calculated Joule-self heating effect (solid circles and line). The inset displays the $C_p\left(T\right)$ data of a single crystal specimen.