Electrical-current-induced magnetic hysteresis in self-assembled vertically aligned $\mathrm{L}{\mathrm{a}}_{2/3}\mathrm{S}{\mathrm{r}}_{1/3}\mathrm{Mn}{\mathrm{O}}_{3}:\mathrm{ZnO}$ nanopillar composites

Rapid Communication

Electrical-current-induced magnetic hysteresis in self-assembled vertically aligned $L a_{2 / 3} S r_{1 / 3} Mn O_{3} : ZnO$ nanopillar composites

W. Pan, P. Lu, J. F. Ihlefeld, S. R. Lee, E. S. Choi, Y. Jiang, and Q. X. Jia

Phys. Rev. Materials 2, 021401(R) – Published 22 February 2018

Abstract

Magnetoresistive random-access memory (MRAM) is poised to become a next-generation information storage device. Yet, many materials challenges remain unsolved before it can become a widely used memory storage solution. Among them, an urgent need is to identify a material system that is suitable for downscaling and is compatible with low-power logic applications. Self-assembled, vertically aligned $L a_{2 / 3} S r_{1 / 3} Mn O_{3} : ZnO$ nanocomposites, in which $L a_{2 / 3} S r_{1 / 3} Mn O_{3}$ (LSMO) matrix and ZnO nanopillars form an intertwined structure with coincident-site-matched growth occurring between the LSMO and ZnO vertical interfaces, may offer new MRAM applications by combining their superior electric, magnetic ( $B$ ), and optical properties. In this Rapid Communication, we show the results of electrical current induced magnetic hysteresis in magnetoresistance measurements in these nanopillar composites. We observe that when the current level is low, for example, 1 µA, the magnetoresistance displays a linear, negative, nonhysteretic $B$ field dependence. Surprisingly, when a large current is used, $I$ > 10 µA, a hysteretic behavior is observed when the $B$ field is swept in the up and down directions. This hysteresis weakens as the sample temperature is increased. A possible spin-valve mechanism related to this electrical current induced magnetic hysteresis is proposed and discussed.

Received 3 November 2017

DOI:https://doi.org/10.1103/PhysRevMaterials.2.021401

Physics Subject Headings (PhySH)

Charge Electrical conductivity Ferromagnetism

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

W. Pan¹, P. Lu¹, J. F. Ihlefeld^1,2,3, S. R. Lee¹, E. S. Choi⁴, Y. Jiang⁴, and Q. X. Jia^5,6

¹Sandia National Laboratories, Albuquerque, New Mexico 87185, USA
²Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904, USA
³Department of Electrical and Computer Engineering, University of Virginia, Charlottesville, Virginia 22904, USA
⁴National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA
⁵Department of Materials Design and Innovation, University at Buffalo - The State University of New York, Buffalo, New York 14260, USA
⁶Department of Physics, Konkuk University, Seoul, 05029, Korea

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Vol. 2, Iss. 2 — February 2018

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Figure 1
Structure characterization of self-assembled vertically aligned LSMO:ZnO nanopillars composites. (a) Schematic diagram of a nanopillars composite sample. (b) High resolution cross-section TEM image. The scale bar is 20 nm. (c) X-ray diffraction (XRD) pattern in the reciprocal lattice. LSMO and LAO peaks are marked.
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Figure 2
Magnetoresistance hysteresis of an LSMO:ZnO nanopillars composite sample. (a) Temperature dependence of the resistance at zero magnetic field. The inset shows the schematic diagram of resistance measurement configuration and dimensions of the specimen. (b)–(e) Normalized magnetoresistance $R_{x x} (B) / R_{x x} (0)$ as a function of $B$ field, with each panel showing a different combination of excitation current $I$ at a fixed measurement temperature of $T = 4 K$ . No hysteresis is observed at $I = 0.1$ (b) and 1 μA (c), while a butterfly-shaped magnetoresistance hysteresis around $B = 0 T$ is observed at $I = 10$ (d) and 50 μA (e). (f) $R_{x x} (B) / R_{x x} (0)$ measured at $T = 277 K$ . The excitation current is 10 μA. No hysteresis is observed at this elevated temperature.
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Figure 3
Magnetic torque measurements. (a) Schematic diagram of the magnetic torque measurement configuration. θ is the tilt angle between the sample normal and the magnetic ( $B$ ) field. (b) Normalized capacitance $C / C_{0}$ as a function of the $B$ field for magnetometry performed at low temperature ( $T = 5 K$ ). The arrows mark the $B$ field sweep directions. The vertical lines mark the positions of the two large peaks at $B \sim \pm 0.2 T$ , respectively. (c) $C / C_{0}$ at $T = 100 K$ . (d) $C / C_{0}$ at $T = 200 K$ .
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Figure 4
Comparison of magnetoresistance and magnetic torque measurements. The positions of the large peaks in the magnetic torque measurement (b) are the same as the $B$ field positions where the maxima occur in $Δ R_{x x}$ (a) when the $B$ field is swept along the same direction. $Δ R_{x x}$ is obtained after subtracting the linear background. This coincidence strongly suggests that the hysteretic resistance behavior is related to the magnetization of the specimen.
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Figure 5
STEM analysis of an LSMO:ZnO nanopillars composite. (a) shows an STEM-HAADF image in plan view. A transition region around ZnO, marked by the red circles, is visible. (b) shows a composite color EDS map, made of zinc $K$ (red), strontium $K$ (blue), lanthanum $L$ (green), and manganese $K$ (cyan) maps. A core-shell structure around the ZnO nanopillars, corresponding to a (La, Mn)-rich and Sr-deficient region, is clearly visible. (c) shows the individual map for the above elements.
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Physical Review Materials

Electrical-current-induced magnetic hysteresis in self-assembled vertically aligned La2/3Sr1/3MnO3:ZnO nanopillar composites

W. Pan, P. Lu, J. F. Ihlefeld, S. R. Lee, E. S. Choi, Y. Jiang, and Q. X. Jia

Phys. Rev. Materials 2, 021401(R) – Published 22 February 2018

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Electrical-current-induced magnetic hysteresis in self-assembled vertically aligned $L a_{2 / 3} S r_{1 / 3} Mn O_{3} : ZnO$ nanopillar composites