Ferromagnetism in van der Waals compound $\mathrm{MnS}{\mathrm{b}}_{1.8}\mathrm{B}{\mathrm{i}}_{0.2}\mathrm{T}{\mathrm{e}}_{4}$

Ferromagnetism in van der Waals compound $MnS b_{1.8} B i_{0.2} T e_{4}$

Yangyang Chen, Ya-Wen Chuang, Seng Huat Lee, Yanglin Zhu, Kevin Honz, Yingdong Guan, Yu Wang, Ke Wang, Zhiqiang Mao, Jun Zhu, Colin Heikes, P. Quarterman, Pawel Zajdel, Julie A. Borchers, and William Ratcliff, II

Phys. Rev. Materials 4, 064411 – Published 11 June 2020

Abstract

The intersection of topology and magnetism represents a new playground to discover novel quantum phenomena and device concepts. In this work, we show that under certain synthetic conditions, a van der Waals single-crystalline compound $MnS b_{1.8} B i_{0.2} T e_{4}$ exhibits a net ferromagnetic state with a Curie temperature of 26 K, in contrast to the fully compensated antiferromagnetic order observed previously for other members of the $Mn {(Sb, Bi)}_{2} T e_{4}$ family. We employ magneto-transport, bulk magnetization, x-ray and neutron scattering studies to illustrate the structural, magnetic, and electrical properties of $MnS b_{1.8} B i_{0.2} T e_{4}$ . Our structural analyses reveal considerable Mn-Sb site mixing and suggest a recently proposed mechanism, where Mn occupying the Sb site mediates a ferromagnetic coupling between Mn layers [Murakami et al., Phys. Rev. B 100, 195103 (2019)], could be at play. Close comparisons made to an antiferromagnetic compound $MnS b_{2} T e_{4}$ illustrate the subtle magnetic interactions of the system and the important role played by local chemistry. The appearance of an unusual anomalous Hall effect in $MnS b_{1.8} B i_{0.2} T e_{4}$ at low temperatures hints at a magnetic ground state different from other members of this family. Our results are an important step in the synthesis and understanding of magnetism in materials with topological characteristics.

Received 19 October 2019
Revised 20 February 2020
Accepted 28 April 2020

DOI:https://doi.org/10.1103/PhysRevMaterials.4.064411

Physics Subject Headings (PhySH)

Anomalous Hall effect Electrical conductivity Ferromagnetism Magnetic phase transitions Magnetotransport Topological insulators

Magnetic systems Van der Waals systems

Electrical techniques Magnetization measurements Neutron diffraction

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Yangyang Chen ^1,3, Ya-Wen Chuang ¹, Seng Huat Lee ^1,2, Yanglin Zhu^1,2, Kevin Honz ¹, Yingdong Guan¹, Yu Wang^1,2, Ke Wang⁵, Zhiqiang Mao^1,2, Jun Zhu^1,*, Colin Heikes ⁴, P. Quarterman ⁴, Pawel Zajdel ⁶, Julie A. Borchers⁴, and William Ratcliff, II^4,7

¹Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
²2D Crystal Consortium, Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
³International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, People's Republic of China
⁴NIST Center for Neutron Research, NIST, Gaithersburg, Maryland 20899, USA
⁵Materials Characterization Laboratory, Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
⁶Institute of Physics, University of Silesia, ul. 75 Pulku Piechoty 1, 41-500, Chorzow, Poland
⁷Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA

^*jxz26@psu.edu

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Vol. 4, Iss. 6 — June 2020

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Figure 1
(a) Schematic stacking order of $Mn {(Sb, Bi)}_{2} T e_{4}$ . (b) An optical image of a typical $MnS b_{1.8} B i_{0.2} T e_{4}$ device in a Hall bar geometry. (c) The Hall resistance $R_{x y} (H)$ on a $MnS b_{1.8} B i_{0.2} T e_{4}$ device at selected temperatures as labeled in the plot. Arrows indicate the field-sweep direction. The green dashed line illustrates the low-field slope $d R_{x y} / d H$ taken at $R_{x y} = 0$ . The inset shows the full-range down sweep of $R_{x y} (H)$ at 2 K. The black dashed line illustrates the high-field slope $d R_{x y} / d H$ . (d) $M (H)$ of a $MnS b_{1.8} B i_{0.2} T e_{4}$ crystal. The coercive field $H_{c} = 310 Oe$ . $1 Oe = (1000 / 4 π) A / m$ . The remnant magnetization $M_{0} = 0.6 μ_{B} / Mn$ . Inset: $M (H)$ to 7 T showing a saturated magnetization of $\sim 1.8 μ_{B} / Mn$ . (e) The anomalous Hall component $Δ R_{x y} (H)$ for the device shown in (b) at selected temperatures. $Δ R_{x y} (H)$ is obtained by subtracting the normal Hall contribution $R_{0} H$ from the measured $R_{x y} (H)$ . The dashed lines illustrate the process of obtaining the saturation field $H_{s}$ for the $T = 30 K$ trace. Fig. S5 of the SM illustrates the determination of $H_{s}$ at $T < 22.5 K$ , when hysteresis is present [38]. Up and down sweeps produce the same $H_{s}$ .
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Figure 2
(a) The low-field slope $d R_{x y} / d H$ as a function of temperature in $MnS b_{1.8} B i_{0.2} T e_{4}$ (magenta circles) and $MnS b_{2} T e_{4}$ (blue squares). The dashed lines are a guide to the eye. (b) The temperature-dependent magnetic susceptibility $M / H$ of a $MnS b_{1.8} B i_{0.2} T e_{4}$ sample measured at three external fields $H = 50$ , 100, and 1000 Oe under both ZFC and FC conditions as labeled in the graph. $H ∥ c$ . The molar magnetic susceptibility $χ_{m} = M V_{m} / H$ , where $V_{m}$ is the volume per gram mole. $1 emu / (mol Oe) = 4 π \times 10^{- 6} m^{3} / mol$ . (c), (d) The main panels show the temperature-dependent elastic neutron scattering centered at the (1 0 1) reflection in $MnS b_{1.8} B i_{0.2} T e_{4}$ (c) and the (1 0 2.5) reflection in $MnS b_{2} T e_{4}$ (d). Mean-field fits (solid lines) yield $T_{C} = 26.3 K$ in (c) and $T_{N} = 19.5 K$ in (d). The insets show scans along the (1 0 L) direction at 5 and 45 K with the * symbol marking the (1 0 1) and (1 0 4) reflections in (c) and the (1 0 2.5) reflection in (d). Larger-range scans from (1 0 4) to (1 0 −4) on both compounds are shown in Fig. S7 to show a clear increase of the (1 0 4) peak with decreasing temperature and the lack of twinning in the $MnS b_{1.8} B i_{0.2} T e_{4}$ samples [38]. Error bars in (c) and (d) represent one standard deviation.
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Figure 3
(a) Moment saturation field $H_{s}$ vs $T$ in $MnS b_{1.8} B i_{0.2} T e_{4}$ obtained from $Δ R_{x y} (H)$ data shown in Fig. 1 and Fig. S5. Solid symbols are data below $T_{C}$ . Open symbols are data above $T_{C}$ and use the right axis. (b) Lower panel: Temperature-dependent magnetoresistance $R_{x x} (T)$ taken at fixed magnetic field as labeled in the plot. The black dashed lines divide the curves into three regions according to the sign of $d R / d T$ . The boundary points are plotted in the upper panel of (b). The symbols follow the notation of (a). (c) Normalized magnetoresistance $MR = [R_{x x} (H) - R_{x x} (0)] / R_{x x} (0) \times 100 %$ at selected temperatures. Arrows indicate field-sweep direction. Note the change of the $y$ scale in different panels.
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Figure 4
The excess anomalous Hall effect in $MnS b_{1.8} B i_{0.2} T e_{4}$ . (a) $R_{x y}^{A + T} (H)$ , which is the same as $Δ R_{x y} (H)$ in Fig. 1 at $T = 2 K$ and with a tilt angle $θ = 56^{\circ}$ as illustrated in the inset. The magenta dashed line is a Langevin fit to the anomalous Hall effect with an uncertainty of $0.9 m Ω$ . The area shaded in green indicates the excess Hall effect contribution $R_{x y}^{T}$ . (b) $R_{x y}^{T} (H)$ at $θ = 0^{\circ}$ and $T = 2$ , 5, and 10 K. Data obtained from up and down sweeps are shifted horizontally to coincide at $H = 0$ . (c) $R_{x y}^{T} (H)$ at $T = 2 K$ and selected tilt angle θ. $R_{peak}^{T}$ is marked by the * symbol. (d) The angular dependence of $R_{peak}^{T}$ at $T = 2 K$ . The right axis labels the effective magnetic field $H_{eff} = R_{peak}^{T} / R_{0}$ .
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Physical Review Materials

Ferromagnetism in van der Waals compound MnSb1.8Bi0.2Te4

Yangyang Chen, Ya-Wen Chuang, Seng Huat Lee, Yanglin Zhu, Kevin Honz, Yingdong Guan, Yu Wang, Ke Wang, Zhiqiang Mao, Jun Zhu, Colin Heikes, P. Quarterman, Pawel Zajdel, Julie A. Borchers, and William Ratcliff, II

Phys. Rev. Materials 4, 064411 – Published 11 June 2020

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Ferromagnetism in van der Waals compound $MnS b_{1.8} B i_{0.2} T e_{4}$