Hysteretic effects and magnetotransport of electrically switched CuMnAs

Jan Zubáč, Zdeněk Kašpar, Filip Krizek, Tobias Förster, Richard P. Campion, Vít Novák, Tomáš Jungwirth, and Kamil Olejník

Phys. Rev. B 104, 184424 – Published 19 November 2021

Abstract

Antiferromagnetic spintronics allows us to explore storing and processing information in magnetic crystals with vanishing magnetization. In this paper, we investigate magnetoresistance effects in antiferromagnetic CuMnAs upon switching into high-resistive states using electrical pulses. By employing magnetic field sweeps up to 14 T and magnetic field pulses up to $\sim 60$ T, we reveal hysteretic phenomena and changes in the magnetoresistance, as well as the resilience of the switching signal in CuMnAs to the high magnetic field. These properties of the switched state are discussed in the context of recent studies of antiferromagnetic textures in CuMnAs.

Received 15 July 2021
Accepted 20 October 2021

DOI:https://doi.org/10.1103/PhysRevB.104.184424

Physics Subject Headings (PhySH)

Antiferromagnetism Magnetic texture Magnetism Magnetoresistance Magnetotransport Spintronics

Antiferromagnets Thin films

Resistivity measurements

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Jan Zubáč ^1,2,*, Zdeněk Kašpar ^1,2, Filip Krizek¹, Tobias Förster³, Richard P. Campion⁴, Vít Novák¹, Tomáš Jungwirth^1,4, and Kamil Olejník^1,†

¹Institute of Physics, Czech Academy of Sciences, Cukrovarnická 10, 162 00 Prague 6, Czech Republic
²Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Prague 2, Czech Republic
³Hochfeld-Magnetlabor Dresden (HLD-EMFL) and Würzburg-Dresden Cluster of Excellence ct.qmat, Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
⁴School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom

^*zubac@fzu.cz
^†olejnik@fzu.cz

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Vol. 104, Iss. 18 — 1 November 2021

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Images

Figure 1
(a) Electrical switching of a typical Hall bar device at 300 K showing relaxation of a signal. Single unipolar 100 $μ s$ writing pulses of two different voltage amplitudes and the longitudinal resistance readout were employed. The dotted lines mark the positions of the individual pulses. (b) Nonrelaxing resistance signal after the electrical switching from a relaxed state ( $R_{r}$ ) to the switched state ( $R_{s}$ ) at 200 K. (c) Magnitude of the signal induced by electrical switching at 200 K evaluated at 200 K during switching [see (b)] and at 2 K as the difference between the switched resistance and the resistance after relaxation [see (d)]. The highest pulse voltage of 32 V corresponds to a current density of $\sim 1.2 \times 10^{7} A / {cm}^{2}$ . The inset shows a scanning electron microscope micrograph of a typical Hall bar device. (d) Outline of the main experiment: After electrical switching at 200 K the sample is rapidly cooled down to a temperature of 2 K, at which MR field-sweep measurements in the quenched switched state are performed. Then the sample is warmed up and kept at a temperature of 300 K for 30 min to recover its equilibrium relaxed state. Afterwards, MR in the relaxed state at 2 K is measured in the same manner and with the same field sweep rate of 0.66 T/min as in the switched state. (e) Temperature dependence of the resistance of a typical Hall bar device measured in the relaxed state (open circles) and switched state (black line). Arrows are used to denote a shift of resistance by $Δ R = R_{s} - R_{r}$ due to the electrical switching by 30 V pulses at 200 K. Both curves were obtained during heating for the current applied along the $[\bar{1} 00]$ CuMnAs direction.
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Figure 2
Magnetoresistance of CuMnAs at 2 K (a) in the high-resistance switched state $R_{s}$ for a switching signal $\sim 8.5 Ω$ and (b) in the low-resistance relaxed state $R_{r}$ . The data were collected for the $j ∥ B ∥ [\bar{1} 00]$ configuration. The dotted line represents the first sweep up after cooling the sample. (c) Difference $R_{s} - R_{r}$ between the switched-state and relaxed-state magnetoresistances, showing the main effects induced by the quench switching: significant hysteretic behavior and a change in the high-field slope. Black lines mark the hysteresis magnitude at 4 T and the slope from the linear fit of the sweep down in the range 10–14 T. Arrows and numbers indicate the development of the hysteretic magnetization process. Further discussion is given in the text.
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Figure 3
(a) Difference MR curves between the switched and relaxed states for various switching signal magnitudes. The data were taken for the $j ∥ B ∥ [\bar{1} 00]$ configuration; the virgin MR curve is not shown. Individual dependencies were further shifted by an arbitrary value for clarity. (b) Development of the hysteresis size and (c) the high-field slope with the switching signal size for the data in (a). The switching signal $(R_{s} - R_{r}) / R_{2 K} = 20 %$ is indicated by a gray vertical line.
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Figure 4
(a) Resistance at 2 K during magnetic field rotations at various field strengths for the $j ∥ [\bar{1} 00]$ and $j ∥ [010]$ current directions. Solid symbols represent the MR data in the switched state after the 30 V electrical pulse at 200 K; open symbols show the MR in the relaxed state. Solid vertical lines indicate the current direction. The individual angular scans were collected at increasing fields from 2 to 7 T; the data for the field rotation from $0^{\circ}$ to $360^{\circ}$ coincided with those taken during rotation from $360^{\circ}$ back to $0^{\circ}$ (not shown). (b) Difference between the switched and relaxed MR data for increasing field strengths. The solid lines represent fits to the $A cos (2 ψ)$ function. (c) The amplitude of differential resistance as obtained by fitting to the $A cos (2 ψ)$ function in (b).
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Figure 5
(a) Magnetoresistance of CuMnAs in the pulsed magnetic field at low temperature. The switched-state MR $R_{s}$ for a switching signal of 7.2 $Ω$ is plotted by a solid line; open symbols show the MR in the relaxed state $R_{r}$ . Data from the sweep up below 10 T had to be omitted due to the large noisy pickup signal (typical for the given type of measurement). The resistance $R_{0}$ in the switched state at zero field immediately before the magnetic field pulse is highlighted by the black cross. (b) Detail of the pulsed-field MR from (a) below 14 T. (c) MR data obtained at a field sweep rate of 0.66 T/min without switching (open symbols) and after electrical switching with a signal magnitude of 6.8 $Ω$ (solid line).
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