Transport mechanisms in manganite-titanate heterojunctions

We have found that the current-voltage characteristics of ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3(-\delta )}∕\mathrm{Nb}:\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ rectifying junctions are quantitatively well described by (thermally assisted) tunneling with an effectively temperature-independent Schottky barrier under no magnetic field, while those of the oxygen deficient junction remarkably deviate from such a simple behavior as magnetic field is applied. These results indicate the junction magnetoresistance arising from magnetic-field changes of the interface band diagram via the strong electron-spin coupling in manganites.

Figure 1

Forward-bias $I\text{−}V$ characteristics for the (a) oxygen-deficient and (b) oxygen-stoichiometric junctions at $0\mathrm{T}$. Characteristics for the oxygen-deficient junction at $8\mathrm{T}$ are shown in (c) as well as in (d) on an enlarged scale. Bold lines are linear fitting on a semilogarithmic scale. (e) Magnetic field dependence of the forward-bias $I\text{−}V$ characteristics for the oxygen deficient junction at $10\mathrm{K}$. (f) Schematic layout of the junction device for $I\text{−}V$ and capacitance measurements.

Figure 2

(a) Saturation current density $J_S\left(T\right)$ and (b) barrier height ${\varphi }_{bn}$ as a function of temperature for the oxygen-deficient junction at $0\mathrm{T}$. $J_S\left(T\right)$ and ${\varphi }_{bn}$ for the stoichiometric junction at $0\mathrm{T}$ are plotted in panels (c) and (d), respectively.

Figure 3

Schematic potential profile for ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3(-\delta )}∕\mathrm{Nb}:\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ Schottky junction under the forward bias of $V$. (a) Thermionic emission, (b) thermally assisted tunneling, and (c) direct tunneling processes from $\mathrm{Nb}:\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ to ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3-\delta }$ are also schematically shown.

Figure 4

Inverse of slope in $\ln J\text{−}V$ plots (dots) and $E_0∕k$ following Eq. (6) (curves) for the (a) oxygen-deficient junction at $0\mathrm{T}$, (b) oxygen-stoichiometric junction at $0\mathrm{T}$, and (c) oxygen deficient junction at $8\mathrm{T}$.

Figure 5

$\ln [J_S\cosh (E_{00}∕kT)∕T]$ plotted as a function of $1∕E_0$ by dots for the oxygen-deficient junction and by triangles for the stoichiometric junction. The data points are connected by dashed lines. Bold lines are linear fits to the data between 400 and $100\mathrm{K}$.

Figure 6

Zero-bias capacitance for the (a) oxygen- deficient and (b) oxygen-stoichiometric junction at 0 and $8\mathrm{T}$.