Modified Kondorsky Domain Reversal in Microstructured Phase-Separated Manganites

TL;DR

The paper investigates how confinement in microstructured, phase-separated manganites alters domain-reversal mechanisms. By fabricating 20 × 100 μm LP5CMO wires and performing magnetotransport measurements across temperature, field, and orientation, the authors show that bulk LP5CMO follows the standard Kondorsky domain-reversal model, while the microstructures exhibit a modified Kondorsky behavior due to local fields from reversed domains, described by $H_C(θ)=\frac{H_{C0}}{\cos θ^*}$ with $θ^* = \arcsin\left( \frac{k \sin θ}{\sqrt{k^2 + 2k \cos θ + 1}} \right)$ and $k = \frac{H_{C0}}{4π M_s}$. Extracted $M_s$ values, representing local reversed-domain magnetization, are smaller than the bulk saturation value, and electric-field effects on magnetic anisotropy are weak at the studied conditions, likely because the samples retain a high FMM fraction near $T_{IM}$. The work demonstrates a magnetotransport approach to probing the competition between shape and magnetocrystalline anisotropy in confined manganite systems and points toward future studies on materials with reduced FMM fractions to enable more substantial electric-field control at low currents.

Abstract

The hole-doped manganite (La$_{1-y}$Pr$_{y}$)$_{0.67}$Ca$_{0.33}$MnO$_3$ (LPCMO) shows electronic phase separation between ferromagnetic metallic (FMM) and anti-ferromagnetic charge-ordered insulating (AFM-COI) regions. In this study, (La$_{0.5}$Pr$_{0.5}$)$_{0.67}$Ca$_{0.33}$MnO$_{3}$ (LP5CMO) microstructures were fabricated using photolithography on thin films grown on (110) NdGaO$_3$ (NGO) substrates. We investigated the domain reversal mechanism of these microstructures through magnetotransport measurements. Our results demonstrate that, while bulk (unpatterned) films follow the standard Kondorsky model for domain reversal, the microstructures obey a modified Kondorsky model. This difference indicates that local magnetic fields from reversed domains significantly influence the coercive field in confined geometries. Although we did not observe a strong electric field effect, this study establishes that magnetotransport measurements are a feasible method for probing the competition between shape and magnetocrystalline anisotropy in manganite microstructures, which could provide an alternative path for controlling magnetic domains at low current densities.

Figures (3)

• Figure 1: Optical microscope image showing the (a) samples in the chip carrier, (b) easy axis sample, and (c) hard axis sample. The double-sided arrow in (c) shows the 100 $\mu$m width of a gold contact. (d) The microstructure in (b) digitally brightened to show that the LP5CMO microstructure on the NGO substrate. The width of the LP5CMO bars (light gray) is 20 $\mu$m. Resistance vs. temperature behavior of (e) the unpatterned LP5CMO thin film, (f) the LP5CMO easy axis microstructure, and (g) the LP5CMO hard axis microstructure. The hysteresis between the warming (higher transition temperature) and cooling (lower transition temperature) cycles is observed for all the samples due to phase coexistence.
• Figure 2: Normalized resistance versus applied magnetic field data taken at 98 K with $V_{\mathrm{cool}}= 5$ V used to determine $H_C$ for both (a) the easy and (b) hard axis devices. $H_{C1}$ and $H_{C2}$ are marked in the figures.
• Figure 3: $H_C$ versus $\theta$ for the easy axis sample at (a) 94K and (b) 98K and for the hard axis sample at (c) 94K and (d) 98K, and the corresponding modified Kondorsky model fits. The Kondorsky model is also shown as a dashed line for comparison.