Probing electronic-phase-separated insulating domains in the metallic phase of patterned perovskite manganite microwires

We investigated the mesoscopic electrical transport properties of micropatterned perovskite manganite (${\text{La}}_{0.5}{\text{Ba}}_{0.5}{\text{MnO}}_3$; LBMO) films that show electronic phase separation between ferromagnetic and $A$-type antiferromagnetic phases. The patterned-wire LBMO film of $10\mu \text{m}$ width showed an insulator-metal (IM) transition associated with a ferromagnetic transition, followed by re-emergence of insulator characteristics below 200 K that did not appear in the unpatterned thin films. By controlling wire width, we were able to probe the phase-separated antiferromagnetic insulating domains, where large first-order IM transitions appeared in the patterned narrow wire with a small channel. Our results show that probing small population of insulating domains in metallic phases and their control by magnetic fields depends strongly on the dimensions of the microchannel.

Figure 1

(Color online) (a) Neutron diffraction patterns of polycrystalline LBMO at 400 and 20 K, indexed to the simple perovskite unit cell, where subscripts N, F, and A represent nuclear, FM, and $A$-type AFM, respectively. (b) Temperature dependence of magnetic diffractions for ${\left(001\right)}_{\text{F}}$ and ${\left(00\frac{1}{2}\right)}_{\text{A}}$.

Figure 2

(Color online) (a) AFM image of the LBMO wire and deposited Pt contacts for the $\rho$ measurements, where $w$ and $l$ represent wire width and probe contact distance, respectively. The inset shows the measurement configuration. Cross sections of (b) patterned wire [line 1 on panel (a)] and (c) valley between the probe contacts [line 2 on panel (a)].

Figure 3

(Color online) $\rho \text{−}T$ curves for patterned wires of dimensions (a) $w=500\mu \text{m}$ and $l=1000\mu \text{m}$, (b) $w=500\mu \text{m}$ and $l=15\mu \text{m}$, (c) $w=10\mu \text{m}$ and $l=1000\mu \text{m}$, and (d) $w=10\mu \text{m}$ and $l=18\mu \text{m}$. Multiple measurement runs for each sample were carried out under the same probe conditions. The inset in panel (a) shows $\rho \text{−}T$ curve of bulk polycrystalline LBMO. Schematic models [insets in panels (b)–(d)] show conduction pathways in the EPS state of LBMO. White represents FM metal and black represents AFM insulator. TCR variations at low temperatures for the patterned wires of dimensions (e) $w=500\mu \text{m}$ and $l=1000\mu \text{m}$, (f) $w=500\mu \text{m}$ and $l=15\mu \text{m}$, and (g) $w=10\mu \text{m}$ and $l=18\mu \text{m}$.

Figure 4

(Color online) $\rho \text{−}T$ curves under 0 and 9 T for patterned wires of dimensions (a) $w=10\mu \text{m}$ and $l=1000\mu \text{m}$ and (c) $w=10\mu \text{m}$ and $l=18\mu \text{m}$. $\rho \left(H\right)/\rho \left(0\right)$ curves showing an MR effect for patterned wires of dimensions (b) $w=10\mu \text{m}$ and $l=1000\mu \text{m}$ and (d) $w=10\mu \text{m}$ and $l=18\mu \text{m}$.