Magnetoresistance anomaly during the electrical triggering of a metal-insulator transition

Pavel Salev, Lorenzo Fratino, Dayne Sasaki, Soumen Bag, Yayoi Takamura, Marcelo Rozenberg, and Ivan K. Schuller

Phys. Rev. B 108, 174434 – Published 20 November 2023

Abstract

Phase separation naturally occurs in a variety of magnetic materials and it often has a major impact on both electric and magnetotransport properties. In resistive switching systems, phase separation can be created on demand by inducing local switching, which provides an opportunity to tune the electronic and magnetic state of the device by applying voltage. Here we explore the magnetotransport properties in the ferromagnetic oxide ${La}_{0.7} {Sr}_{0.3} {MnO}_{3}$ (LSMO) during the electrical triggering of an intrinsic metal-insulator transition (MIT), which produces volatile resistive switching. This switching occurs in a characteristic spatial pattern, i.e., the formation of a high-resistance barrier perpendicular to the current flow, enabling an electrically actuated ferromagnetic-paramagnetic-ferromagnetic phase separation. At the threshold voltage of the MIT triggering, both anisotropic and colossal magnetoresistances exhibit anomalies including a large increase in magnitude and a sign flip. Computational analysis revealed that these anomalies originate from the coupling between the switching-induced phase separation state and the intrinsic magnetoresistance of LSMO. This work demonstrates that driving the MIT material into an out-of-equilibrium resistive switching state provides the means for electrical control of the magnetotransport phenomena.

Received 21 August 2023
Accepted 24 October 2023

DOI:https://doi.org/10.1103/PhysRevB.108.174434

Physics Subject Headings (PhySH)

Magnetic phase transitions Magnetoelectric effect Metal-insulator transition Resistive switching

Complex oxides Magnetic thin films

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Pavel Salev ¹, Lorenzo Fratino ^2,3, Dayne Sasaki ⁴, Soumen Bag², Yayoi Takamura ⁴, Marcelo Rozenberg ², and Ivan K. Schuller⁵

¹Department of Physics & Astronomy, University of Denver, Denver, Colorado 80210, USA
²Université Paris-Saclay, CNRS Laboratoire de Physique des Solides, 91405 Orsay, France
³Laboratoire de Physique Théorique et Modélisation, CNRS UMR 8089, CY Cergy Paris Université, 95302 Cergy-Pontoise Cedex, France
⁴Department of Materials Science and Engineering, University of California Davis, Davis, California 95616, USA
⁵Department of Physics and Center for Advanced Nanoscience, University of California San Diego, La Jolla, California 92093, USA

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Issue

Vol. 108, Iss. 17 — 1 November 2023

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Images

Figure 1
(a) Schematic of the resistive switching measurement setup. Optical image shows a $50 \times 100 μ m^{2}$ LSMO Hall bar device. Scale bar is 25 µm. (b) Global I-V curve of the LSMO Hall bar showing the volatile low-to-high resistance switching. (c) Local voltages across the Hall bar arms recorded during the switching. At the 14.5-V threshold voltage, local voltage $V_{1}$ across the top Hall bar section abruptly increases indicating the low-to-high resistance switching. (d) MOKE maps of the Hall bar recorded under the applied voltage of 10 V (left) and 15 V (right). While the 10-V map is uniformly ferromagnetic, the 15-V map shows the formation of a PM barrier in the top section indicating the local MIT triggering. Scale bars are 25 µm. All measurements were performed at 100 K.
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Figure 2
(a) Schematic of the AMR measurement setup. (b) Resistance-angle curves in equilibrium (0.1 V) showing the AMR of ΔR/ $R$ ∼ 0.2%. (c) Resistance-angle curves recorded at the MIT triggering threshold (14.5 V) in the Hall bar sections containing the PM barrier (top) and in the FM section (bottom). The AMR magnitude increases and its sign flips in the PM barrier section. (d) AMR magnitude as a function of applied voltage. The AMR anomaly can be observed at the MIT triggering threshold. AMR measurements in (b)–(d) were performed in 1-kOe applied field. (e) AMR amplitude dependence on the applied magnetic field in equilibrium (gray lines) and at the MIT triggering threshold (red and blue lines) for the PM barrier (top) and FM metal (bottom) Hall bar sections. At the switching, the AMR amplitude shows a persistent increase with increasing field. All measurements were done at 100 K.
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Figure 3
Small-field magnetoresistance measurements with the magnetic field parallel (a) and perpendicular (b) to the electric current in equilibrium (0.1 V, gray lines) and at the MIT triggering threshold voltage (14.5 V, red and blue lines) corresponding to the two sections of the Hall bar device, $R_{1}$ and $R_{2}$ [defined in Fig. 2]. During resistive switching, the magnetoresistance of the PM barrier section ( $R_{1}$ ) flips sign. The shape and magnitude differences between $R_{| |} − H$ and $R_{⊥} − H$ curves indicate the change of magnetic anisotropy during the switching. All measurements were performed at 100 K.
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Figure 4
(a) Large-field magnetoresistance measurements at the MIT triggering threshold voltage (14.5 V). The R-H curve of the PM barrier section of the Hall bar (top, red line) exhibits conventional negative CMR. The R-H curve of the FM metal section shows an anomalous positive CMR. (b) Magnetoresistance at 20-kOe field as a function of the applied voltage. Similar to AMR in Fig. 2, CMR shows a strong anomaly at the MIT threshold triggering voltage. $R_{1}$ and $R_{2}$ notations are defined in Fig. 2. All measurements were performed at 100 K.
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Figure 5
(a) Schematic of the hybrid resistor network + Ising model. (b), (c) Magnetic field dependence of the resistance (b) and magnetization profiles (c) across the switching device length at an applied voltage above the MIT triggering threshold. The formation of a high-resistance PM barrier at the device center is clearly visible. The inset in (b) shows a zoom-in of the resistance profile in a metallic region of the device. The resistance of the metallic regions increases with increasing magnetic field, which yields a positive magnetoresistance. (d) Magnetic field dependence of the resistance (black curve) and width (green curve) of the PM barrier. (e) Temperature of the PM barrier (red curve) and metallic matrix (blue curve) as a function of the magnetic field. (f) Temperature of the PM barrier (red curve) and metallic matrix (blue curve) as a function of the angle between the magnetization and current.
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