Magnetism and magnetoelastic effect in 2D van der Waals multiferroic CuCrP2S6

Abstract

We report a magnetic and neutron diffraction study on the ground state magnetism and field evolution of single crystal van der Waals multiferroic CuCrP2S6. The ordered moments align along the b axis in the A-type antiferromagnetic configuration with a spin-flop transition along the same direction. Field application along a introduces a smooth transition to a fully-polarized ferromagnetic state via in-plane spin rotation. These findings resolve the ambiguity of the ground state magnetization direction in CuCrP2S6 and uncover its field responses, providing a firm basis for future magnetoelectric study. A magnetoelastic coupling effect connecting the interlayer spacing and the magnetic order was further revealed, highlighting the out-of-plane strain as an effective control knob for tuning magnetism both in this system and in related van der Waals magnets.

Figures (5)

• Figure 1: (a) Crystal structure of CuCrP$_2$S$_6$ in the AFE state. (b) Field cool magnetization $M_a$ and $M_b$ along the $a$ and $b$ crystallographic axes, respectively. Inset shows the refined magnetic structure. (c) Field dependence of $M_b$ at selective temperatures. Inset highlights the spin-flop transition in the low field regime. (d) Derivative of the $M_b$ with respect to the field strength. The peak position defines the spin-flop transition critical field $H_{\rm SF}$.
• Figure 2: (a) Neutron diffraction pattern in the $(0KL)$ scattering plane at $T = 5$ K (top) and $T = 50$ K (bottom) at zero field. Orange arrows mark the magnetic peaks from other structural domains. (b) The temperature dependence of the (0, 0, 1) magnetic peak intensity at zero field. The solid line is a power law fit of $I\propto|t|^{2\beta}$ with the reduced temperature $t=(T_{\rm N}-T)/T_{\rm N}$. The upper inset shows the co-aligned single crystal array used in the neutron measurements. The lower inset shows the $\log-\log$ plot with a linear fit in the range $|t|<0.1$ to determine $\beta$.
• Figure 3: Field evolution of the magnetic structure of CCPS with $a$-axis in-plane field. (a) Field dependence of the (0, 0, 1) and (0, 2, 0) peak intensities at $T$ = 27 K. Insets illustrate the evolution of the magnetic structure with increasing field. The solid line is the model fit and the dashed line is guide to the eye. (b) Field dependence of the in-plane spin canting angle $\theta$. Symbols are experimental values obtained via fitting the (0, 0, 1) peak intensity at different temperatures, solid lines are model predicted values using the stacking model. The dashed line marks the fully-polarized state with $\theta$ = 90$^\circ$.
• Figure 4: Magnetoelastic coupling effect. (a) Temperature dependence of (0, 0, 1) magnetic peak intensity and the interlayer spacing under $H$ = 1.2 T along the $a$ direction. The solid line is a power law fit. (b) Field evolution of the interlayer spacing at $T$ = 15 K and 22 K.
• Figure 5: $T$-$H$ phase diagram of the magnetic structure in CCPS. Insets illustrate the magnetic structure at $H$ = 0 T, the spin-flop AFM configuration at $H_b > H_{\rm SF}$. Colored symbols are obtained from neutron diffraction results with field applied along the $a$ direction.