Piezomagnetic transport in van der Waals noncoplanar Antiferromagnets

TL;DR

This work demonstrates piezomagnetic control of transport in van der Waals noncoplanar antiferromagnets CoNb$_3$S$_6$ and CoTa$_3$S$_6$ by applying uniaxial strain with a flexible substrate. The authors show linear modulation of the antiferromagnetic transition temperature $T_N$ and coercive field $H_c$, consistent with strain-induced tuning of exchange interactions, and directly tune the spontaneous Hall effect through Berry-curve changes, indicating a strain-controlled Berry curvature. Scaling analysis reveals an intrinsic Berry-curvature mechanism dominating the spontaneous Hall response under strain, rather than magnetization-driven effects. The results establish piezomagnetism as a robust route to manipulate antiferromagnetic transport in vdW magnets, paving the way for straintronic and spintronic applications in low-dimensional magnetic systems.

Abstract

The piezomagnetic effect-strain-induced linear modulation of magnetization, arises in magnets with broken time-reversal symmetry (BTRS), offering a pathway to bidirectional strain-based control of magnetism, which is an essential straintronic and spintronic functionality in solids. Metallic antiferromagnets with BTRS provide an ideal platform to study this effect through transport measurements, yet experimental demonstrations are limited. Van der Waals (vdW) nanomagnets, with their mechanical flexibility, are particularly promising for realizing large piezomagnetic responses and effective transport control. Here we demonstrate piezomagnetic control of electronic transport in nano-devices of the vdW antiferromagnets CoNb$_3$S$_6$ and CoTa$_3$S$_6$, archetypal vdW metals with BTRS that exhibit a spontaneous Hall effect. Applying uniaxial strain linearly modulates both the antiferromagnetic transition temperature and coercive field, consistent with strain-driven tuning of exchange coupling, key signatures of the piezomagnetic effect. Moreover, spontaneous Hall effect is controllable via strain, evidencing piezomagnetic tuning of Berry curvature and its associated geometric transport. These findings establish piezomagnetism as a powerful route to manipulate antiferromagnetic transport, opening avenues for straintronic and spintronic applications in vdW magnetic systems.

Figures (4)

• Figure 1: Crystal structure, magnetic order, and the spontaneous Hall effect in van der Waals antiferromagnet CoNb$_3$S$_6$ (A) Schematic of the crystal structure of CoNb$_3$S$_6$. (B) Two distinct non-coplanar antiferromagnetic orders with broken time reversal symmetry (A and B domains). Each domain shows opposite sign of scalar spin chirality ($\chi_{ijk}$) and resultant spontaneous Hall effect. (C) Optical microscope image of a nano-device fabricated on flexible substrate for electronic transport measurements. (D) Temperature dependence of zero field ($B$ = 0) longitudinal resistivity ($\rho_{xx}$). Kink corresponds to the antiferromagnetic transition at Neel temperature, $T_N$. (E) Temperature dependence of spontaneous Hall resistivity ($\rho_{yx}^{SHE}$) under $B$ = 0. Red and blue curves represent the different domain contributions selected by field cooling ($B \parallel c$) process. (F) Magnetic field dependence of $\rho_{yx}$, recorded just below $T_N$ (at 25 K). The red and blue curves correspond to magnetic-field switchable domains via out of plane magnetic field. Insets of (D), (E), (F): illustrate the experimental configurations.
• Figure 2: Strain modulation of antiferromagnetic state in CoNb$_3$S$_6$. (A) Experimental set-up for strain application using bending stage and flexible substrate. Flexible polyethylene naphthalate (PEN) substrate, which contains the exfoliated flakes of CoNb$_3$S$_6$, is sandwiched between a curved Cu-stage and a fixture. (B) Schematics of the application of uniaxial strain. By changing the radius of curvature of substrate, we can achieve both tensile ($\epsilon$$>$ 0) and compressive strain ($\epsilon$$<$ 0), as well as unstrained state ($\epsilon$ = 0). (C) Temperature dependence of longitudinal resistance under various applied uniaxial strain in $B$ = 0. Red and purple arrows indicate $T_N$ for -2 % and +2 % strains, respectively. (D) Magnetic field dependence of $R_{yx}$ under applied strain at 25 K. Dashed grey arrow is a guide to the eye to show Hc evolution with strain magnitudes. (E), (F) Strain dependence of the $H_c$ (at 25 K) and $T_N$ (at $B$ = 0), respectively. (G) Schematics of spin configurations and their modulations under strain. Top, middle and bottom figures correspond to compressive ($\epsilon$$>$ 0), unstrained ($\epsilon$ = 0) and tensile ($\epsilon$$<$ 0) strain, respectively. The canting angle, and exchange interactions are assumed to be modulated under strain as in the previously reported case of piezomagnetic effect in non-collinear spin structures (see supplementary materials note 7).
• Figure 3: Piezomagnetic control of spontaneous Hall effect. (A) Generation of spontaneous magnetization ($M_{net}$) in real space by piezomagnetic effect. Orange arrow indicates a direction of $M_{net}$ under tensile strain. Under the strain, spins will change the canted angles, effectively creating net magnetic moment along the $z$ axis. (B) Schematic of strain modulation of Berry curvature and spontaneous Hall effect. (C) Temperature dependence of spontaneous Hall conductivity ($\sigma_{xy}^{SHE}$) recorded in various strain magnitudes (-0.015 $\leq$$\epsilon$$\leq$ +0.015). (D) The strain variation of $\sigma_{xy}^{SHE}$ at the lowest temperature (5 K). (E)$\sigma_{xy}^{SHE}$ - $\sigma_{xx}$ plot for all temperature below 15 K with various strain magnitudes (-0.015 $\leq$$\epsilon$$\leq$ +0.015). Dashed grey line refers to the exponent $\alpha$=1.8 (see text for details). (F) Comparison of strain controlled spontaneous Hall conductivity (or resistivity) in various magnets with BTRS. The dashed lines correspond to data from multiple thin film samples with different strains, while the solid lines represent data obtained from variable strain on a single specimen. The open (filled) symbols indicate Hall conductivity (resistivity).
• Figure 4: Strain-tunable anisotropy and antiferromagnetic transport in CoTa$_3$S$_6$ (A) Temperature dependence of longitudinal resistance ($R_{xx}$) measured under various strain magnitudes under $B$ = 0. Insets show the optical microscope image of the device and schematics of nematic domains. (B))- (C) Magnetoresistance B and Hall effect C at 5 K recorded under various fixed strains. Dashed line showing the evolution of coercive field with strain. (D)- (F) Strain dependences of Neel temperatures ($T_{N1}$ and $T_{N2}$), coercive field ($H_c$), and Hall angle (tan $\theta_H$). $H_c$ and tan $\theta_H$ are extracted from the data at 5 K.