Anisotropic anomalous transport in the kagome-based topological antiferromagnetic ${\mathrm{Mn}}_{3}\text{Ga}$ epitaxial thin films

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Anisotropic anomalous transport in the kagome-based topological antiferromagnetic ${Mn}_{3} Ga$ epitaxial thin films

M. Raju, Ralph Romero, III, Daisuke Nishio-Hamane, Ryota Uesugi, Mihiro Asakura, Zhenisbek Tagay, Tomoya Higo, N. P. Armitage, Collin Broholm, and Satoru Nakatsuji

Phys. Rev. Materials 8, 014204 – Published 26 January 2024

Abstract

${Mn}_{3} X$ ( $X = Sn$ , Ge, Ga) kagome Weyl semimetals have attracted significant research interest due to their large anomalous Hall, thermal, and optical effects originating from their nontrivial band topology. These large topological effects together with the antichiral antiferromagnetic order that can be manipulated through various experimental means provide unique platforms for developing high-speed spintronics. ${Mn}_{3} Ga$ is known to have the largest Néel temperature ( $T_{N} \approx 480$ K), which is useful for developing antiferromagnetic spintronics. Here, we establish the epitaxial growth of antiferromagnetic ${Mn}_{3} Ga$ films by magnetron sputtering and present their structure, magnetotransport, terahertz properties, and exchange bias effect in ${Mn}_{3} Ga$ /NiFe bilayers, establishing their remarkable properties essential for future investigations towards device applications.

Received 26 August 2023
Accepted 2 January 2024

DOI:https://doi.org/10.1103/PhysRevMaterials.8.014204

Physics Subject Headings (PhySH)

Magnetotransport Topological materials

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

M. Raju ^1,*, Ralph Romero, III ¹, Daisuke Nishio-Hamane², Ryota Uesugi ², Mihiro Asakura³, Zhenisbek Tagay¹, Tomoya Higo^2,3, N. P. Armitage^1,5, Collin Broholm¹, and Satoru Nakatsuji ^{1,2,3,4,5,†}

¹Institute for Quantum Matter, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
²Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
³Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
⁴Trans-Scale Quantum Science Institute, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
⁵Canadian Institute for Advanced Research, Toronto, Ontario M5G 1M1, Canada

^*mraju5@jhu.edu
^†snakats1@jhu.edu

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Vol. 8, Iss. 1 — January 2024

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Figure 1
X-ray diffraction and cross-sectional HRTEM results for the $a b$ -axis and $c$ -axis oriented ${Mn}_{3} Ga$ samples. Schematics for thin film stacks and antichiral spin structures expected (a) for the $a b$ -axis oriented ${Mn}_{3} Ga$ film stack, i.e., MgO(110)/W(7 nm)/ ${Mn}_{3} Ga$ (40 nm)/ ${Al}_{2} O_{3}$ (5 nm), and (g) for the $c$ -axis oriented ${Mn}_{3} Ga$ film stack ${Al}_{2} O_{3}$ (0001)/Ru(5 nm)/ ${Mn}_{3} Ga$ (40 nm)/ ${Al}_{2} O_{3}$ (5 nm). (b), (c) $θ − 2 θ$ and in-plane $ϕ$ scans for the $a b$ -axis oriented ${Mn}_{3} Ga (40$ nm) film. [(d)–(f)] Cross-sectional view of the HRTEM sample, experimental and simulated electron diffraction patterns, and cross-sectional high-resolution TEM image for $a b$ -axis oriented ${Mn}_{3} Ga$ (40 nm) film. (h), (i) $θ − 2 θ$ and in-plane $ϕ$ scans of the $c$ -axis oriented ${Mn}_{3} Ga$ (40 nm) film. $θ − 2 θ$ scans for bare MgO(110) and ${Al}_{2} O_{3}$ (0006) substrates shown in panels (b) and (h) are also recorded for reference. [(j)–(l)] Cross-sectional view of the HRTEM sample, experimental and simulated electron diffraction patterns, and cross-sectional high-resolution TEM image for $c$ -axis oriented ${Mn}_{3} Ga$ (40 nm) film.
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Figure 2
Magnetization results for the $a b$ -axis and the $c$ -axis oriented ${Mn}_{3} Ga$ films. (a) Comparison of the magnetization vs field $[M (B)]$ curve measured at 300 K for $a b$ -axis and $c$ -axis oriented samples. The inset to panel (a) shows the low field evolution of the $M (B)$ curve. (b) In-plane magnetization vs temperature $[M (T)]$ measured between 300 and 600 K for $a b$ -axis and $c$ -axis oriented samples. Data are normalized to the magnetization value at 300 K, and measurement is performed at $B = 0$ T after saturating the sample at $B = 5$ T. The error bar in the estimated value of Néel temperature represents uncertainty in the sample temperature. (c) Temperature dependence of the zero-field cooled (ZFC) and field cooled (FC) magnetization for the $a b$ -axis and $c$ -axis oriented ${Mn}_{3} Ga$ samples, measured at $B = 0.02$ T. (d) Numerical derivative $d M / d T$ profiles of the $M$ vs $T$ data shown in panel (c).
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Figure 3
DC anomalous Hall effect of $a b$ -axis and $c$ -axis oriented ${Mn}_{3} Ga$ (40 nm) samples. (a) Field dependent total DC Hall resistivity $[ρ_{y x} (B)]$ of $a b$ -axis and $c$ -axis oriented ${Mn}_{3} Ga$ (40 nm) samples recorded at 300 K. Red solid lines show a linear fit to the high field (4.5–9 T) Hall data highlighting the slope. (b) Temperature dependent DC Hall resistivity $[ρ_{y x}^{{Mn}_{3} Ga} (T)]$ and longitudinal resistivity $[ρ_{x x}^{{Mn}_{3} Ga} (T)]$ corresponding to $a b$ -axis oriented ${Mn}_{3} Ga$ at zero magnetic field. $ρ_{y x}^{{Mn}_{3} Ga} (T)$ and $ρ_{x x}^{{Mn}_{3} Ga} (T)$ are estimated by accounting for the current shunting through the W(7 nm) buffer layer [19]. (c) High-temperature evolution of $ρ_{y x}^{{Mn}_{3} Ga} (T)$ , suggesting $ρ_{y x}^{{Mn}_{3} Ga} \approx 0$ at $\approx 480$ K, which is close to the expected Néel temperature for ${Mn}_{3} Ga$ . Square symbols refer to data measured in PPMS between 200 and 400 K, and diamond symbols refer to data measured in a custom-built high-temperature probe between 300 and 500 K. (d) Estimated DC anomalous Hall conductivity ( $σ_{y x} = - ρ_{y x} / ρ_{x x}^{2}$ ) from the data shown in panel (b), where error bars represent the possible variation in the estimated magnitude of $σ_{y x}$ .
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Figure 4
Terahertz anomalous Hall effect of $a b$ -axis and $c$ -axis oriented ${Mn}_{3} Ga$ (40 nm) samples. (a) Schematic of the magneto time-domain terahertz spectrometer used for measuring Faraday rotation. (b) Terahertz Faraday rotation for $a b$ -axis and $c$ -axis oriented ${Mn}_{3} Ga$ samples recorded at various fixed temperatures and frequency of 1.5 THz, as the applied field is reduced to zero from $\pm 2.5$ T. (c) Field evolution of terahertz Hall conductivity (estimated from field evolution of Faraday rotation) and its comparison with DC anomalous Hall conductivity for the $a b$ -axis ${Mn}_{3} Ga$ sample recorded at 100 K. For comparison, the terahertz Hall data are extrapolated to $ω = 0$ (see Fig. S3, Supplemental Material [29]). (d) Temperature evolution of terahertz Hall conductivity at zero field for the $a b$ -axis oriented ${Mn}_{3} Ga$ sample.
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Figure 5
Magnetoresistance for $a b$ -axis and $c$ -axis oriented ${Mn}_{3} Ga$ films. (a, b) Magnetoresistance— $(Δ ρ_{x x} = \frac{[ρ_{x x} (B) - ρ_{x x} (B = 0)]}{ρ_{x x} (B = 0)} \times 100),$ measured for $a b$ -axis oriented ${Mn}_{3} Ga$ film at various temperatures in $B ⊥ I$ and $B ∥ I$ configuration respectively. (c) Increase in negative magnetoresistance (NMR), the difference of the data shown in panels (a) and (b) estimated as $Δ ρ_{x x} (B ∥ I) - Δ ρ_{x x} (B ⊥ I)$ for $a b$ -axis oriented ${Mn}_{3} Ga$ film. (d, e) Magnetoresistance ( $Δ ρ_{x x}$ ) measured for $c$ -axis oriented ${Mn}_{3} Ga$ film at various temperatures in $B ⊥ I$ and $B ∥ I$ configuration respectively. (f) Increase in negative magnetoresistance, the difference of the data shown in panels (d) and (e), estimated as $Δ ρ_{x x} (B ∥ I) - Δ ρ_{x x} (B ⊥ I)$ for $c$ -axis oriented ${Mn}_{3} Ga$ film.
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Figure 6
Exchange bias effect in ${Mn}_{3} Ga$ (40 nm)/NiFe(10 nm) bilayers. (a) Magnetization loop at 5 K for $\pm 7$ T cooling field conditions for $a b$ -axis oriented ${Mn}_{3} Ga$ (40 nm)/NiFe(10 nm) bilayer. (b) Normalized magnetoresistance (MR) measured for $a b$ -axis oriented ${Mn}_{3} Ga$ (40 nm)/NiFe(10 nm) bilayer at 100 and 10 K. (c) Temperature evolution of exchange bias ( $B_{EB}$ ) and coercivity ( $B_{C}$ ) of the $a b$ -axis oriented ${Mn}_{3} Ga$ (40 nm)/NiFe(10 nm) bilayer estimated from MR measurements. (d) Magnetization loop at 5 K for $\pm 7$ T cooling field conditions for $c$ -axis oriented ${Mn}_{3} Ga$ (40 nm)/NiFe(10 nm) bilayer. (e) Normalized MR measured for $c$ -axis oriented ${Mn}_{3} Ga$ (40 nm)/NiFe(10 nm) bilayer at 100 and 10 K. (f) Temperature evolution of $B_{EB}$ and $B_{C}$ of the $c$ -axis oriented ${Mn}_{3} Ga$ (40 nm)/NiFe(10 nm) bilayer estimated from MR measurements. Vertical dotted lines in panel (c) and (f) mark onset of exchange bias effect and the blocking temperature.
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Physical Review Materials

Anisotropic anomalous transport in the kagome-based topological antiferromagnetic Mn3Ga epitaxial thin films

M. Raju, Ralph Romero, III, Daisuke Nishio-Hamane, Ryota Uesugi, Mihiro Asakura, Zhenisbek Tagay, Tomoya Higo, N. P. Armitage, Collin Broholm, and Satoru Nakatsuji

Phys. Rev. Materials 8, 014204 – Published 26 January 2024

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Anisotropic anomalous transport in the kagome-based topological antiferromagnetic ${Mn}_{3} Ga$ epitaxial thin films