Colossal magnetoresistance via avoiding fully polarized magnetization in the ferrimagnetic insulator ${\mathrm{Mn}}_{3}{\mathrm{Si}}_{2}{\mathrm{Te}}_{6}$

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Colossal magnetoresistance via avoiding fully polarized magnetization in the ferrimagnetic insulator ${Mn}_{3} {Si}_{2} {Te}_{6}$

Yifei Ni, Hengdi Zhao, Yu Zhang, Bing Hu, Itamar Kimchi, and Gang Cao

Phys. Rev. B 103, L161105 – Published 14 April 2021

Abstract

Colossal magnetoresistance is of great fundamental and technological significance and exists mostly in the manganites and a few other materials. Here we report colossal magnetoresistance that is starkly different from that in all other materials. The stoichiometric ${Mn}_{3} {Si}_{2} {Te}_{6}$ is an insulator featuring a ferrimagnetic transition at 78 K. The resistivity drops by seven orders of magnitude with an applied magnetic field above 9 T, leading to an insulator-metal transition at up to 130 K. However, the colossal magnetoresistance occurs only when the magnetic field is applied along the magnetic hard axis and is surprisingly absent when the magnetic field is applied along the magnetic easy axis where magnetization is fully saturated. The anisotropy field separating the easy and hard axes is 13 T, unexpected for the Mn ions with nominally negligible orbital momentum and spin-orbit interactions. Double exchange and Jahn-Teller distortions that drive the hole-doped manganites do not exist in ${Mn}_{3} {Si}_{2} {Te}_{6}$ . The phenomena fit no existing models, suggesting a unique, intriguing type of electrical transport.

Received 31 December 2020
Accepted 1 April 2021

DOI:https://doi.org/10.1103/PhysRevB.103.L161105

Physics Subject Headings (PhySH)

Colossal magnetoresistance Ferrimagnetism Frustrated magnetism Magnetic anisotropy

Insulators

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Yifei Ni¹, Hengdi Zhao¹, Yu Zhang¹, Bing Hu ^1,2, Itamar Kimchi³, and Gang Cao ^1,*

¹Department of Physics, University of Colorado at Boulder, Boulder, Colorado 80309, USA
²School of Mathematics and Physics, North China Electric Power University, Beijing 102206, China
³School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA

^*gang.cao@colorado.edu

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Vol. 103, Iss. 16 — 15 April 2021

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Figure 1
Crystal structure. (a) The crystal structure highlighting the three-dimensional nature and bond distances for Mn1-Mn1 and Mn1-Mn2 marked by the white dashed lines. The third-nearest-neighbor interaction denoted by the diagonal dashed line proves consequential [23]. (b) The magnetic structure based on Ref. [23]. (c) The temperature dependence of the $a$ and $c$ axis, and the relative changes in the $a$ and $c$ axis against the values at 300 K (right scale). (d) A crystal sample showing the $a b$ plane.
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Figure 2
Magnetic properties. The temperature dependence of (a) the $a b$ -plane magnetization $M_{a b}$ and (b) the $c$ -axis magnetization $M_{c}$ at various magnetic fields. Inset in (a): $M_{a b}$ highlighting the correlated behavior at $T_{C} < T < T^{*}$ . Inset in (b): $M_{a b}$ ( $T$ ) and $M_{c}$ ( $T$ ) at 14 T. (c) The isothermal magnetization $M_{a b}$ and $M_{c}$ at 10 K up to 14 T highlighting the anisotropy field. Note that $M_{a b}$ saturates at $μ_{o} H = 0.05 T$ and $M_{c}$ approaches $M_{s}$ at $μ_{o} H \geq 13 T$ .
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Figure 3
Transport properties. The temperature dependence of (a) the $a b$ -plane resistivity $ρ_{a b}$ and (b) the $c$ -axis resistivity $ρ_{c}$ at various magnetic fields applied along the $c$ axis. Note that $ρ_{a b}$ drops by seven orders of magnitude or 99.999 99% at low temperatures and the $T_{IM}$ shifts up to 130 K at 14 T. Inset in (a) $ρ_{a b}$ highlighting anomaly corresponding to $T^{*}$ . Inset in (b) showing $ρ_{a b} > ρ_{c}$ .
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Figure 4
Anisotropy and CMR below and above $T_{C}$ . The magnetic field dependence at 10 K of (a) $ρ_{a b}$ ( $H | | a b$ ) and $ρ_{a b}$ ( $H | | c$ ) and $M_{a b}$ and $M_{c}$ (dashed lines, right scale), and (b) the corresponding $Δ ρ_{a b} / ρ_{a b}$ ( $H | | a b$ ) and $Δ ρ_{a b} / ρ_{a b}$ ( $H | | c$ ), where $Δ ρ_{a b} / ρ_{a b} = [ρ_{a b} (H) - ρ_{a b} (0)] / ρ_{a b} (0)$ . Note that $Δ ρ_{a b} / ρ_{a b}$ ( $H | | a b$ ) is ∼20% at $μ_{o} H_{| | a b} = 14 T$ and $M_{a b} = M_{s}$ whereas $Δ ρ_{a b} / ρ_{a b}$ ( $H | | c$ ) is already 97.50% at $μ_{o} H_{| | c} = 3 T$ at which $M_{c} = 0.77 μ_{B} / Mn < 0.5 M_{s}$ and 99.999 99% at $μ_{o} H_{| | c} > 9 T$ at which $M_{c} < M_{s}$ . (c) The field dependence of $Δ ρ_{a b} / ρ_{a b}$ ( $H | | c$ ) at 5, 30, and 120 K. Note that MR is still 85% at 120 K. Inset: The low-field scaling plot of $Δ ρ_{a b} / ρ_{a b} (H | | c) = C {(M_{c} / M_{s})}^{2}$ for $μ_{o} H_{| | c} < 3.2 T$ and $80 K > T_{C}$ , yielding $C = 105$ (dashed line). (d) The angular dependence of $ρ_{a b}$ at 14 T and various temperatures. Inset: The angle θ measures the angle between $H$ and the $c$ axis.
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Figure 5
Hall effect, carrier density, and heat capacity. (a) The field dependence of the Hall resistivity $ρ_{x y}$ at representative temperatures. Note the AHE persisting up to $T > T_{C}$ . Upper inset: The Hall sample with electrical leads and $H$ pointing out of the page. Lower inset: $ρ_{x y} (H)$ at 200 K, showing the linear $H$ dependence. (b) The temperature dependence of the carrier density $n$ and $ρ_{a b}$ at $μ_{o} H_{| | c} = 14 T$ (red dashed line, right scale). Note that $n$ closely tracks $ρ_{a b}$ . (c) The heat capacity $C$ ( $T$ ) at zero field (blue) and $μ_{o} H_{| | c} = 14 T$ (red) plotted as $C$ ( $T$ )/ $T$ vs $T^{2}$ . Note that the linear- $T$ term due to the critical spin fluctuations is suppressed by $H$ (see inset).
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Physical Review B

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Colossal magnetoresistance via avoiding fully polarized magnetization in the ferrimagnetic insulator ${Mn}_{3} {Si}_{2} {Te}_{6}$

Yifei Ni, Hengdi Zhao, Yu Zhang, Bing Hu, Itamar Kimchi, and Gang Cao

Phys. Rev. B 103, L161105 – Published 14 April 2021

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Physical Review B

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Colossal magnetoresistance via avoiding fully polarized magnetization in the ferrimagnetic insulator Mn3Si2Te6

Yifei Ni, Hengdi Zhao, Yu Zhang, Bing Hu, Itamar Kimchi, and Gang Cao

Phys. Rev. B 103, L161105 – Published 14 April 2021

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Colossal magnetoresistance via avoiding fully polarized magnetization in the ferrimagnetic insulator ${Mn}_{3} {Si}_{2} {Te}_{6}$