Magnetism and magnetoelectric coupling in the van der Waals antiferromagnet CuCr1−xVxP2S6

The van der Waals (vdW) two-dimensional (2D) material copper chromium thiophosphate ($\mathrm{CuCr}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$) exhibits robust magnetoelectric (ME) coupling with coexisting type-I and II multiferroic characteristics, suggesting significant potential for ME applications. Nevertheless, the weak coupling strength has limited its potential for applications. Here, we systematically investigate the magnetic and electrical properties of the V-doped $\mathrm{CuCr}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$ solid solution $\mathrm{CuC}{\mathrm{r}}_{1\ensuremath{-}x}{\mathrm{V}}_{x}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$ combining experiments and density functional calculations. Substitution of V for Cr induces a gradual transition from A-type antiferromagnetic (AFM) to ferromagnetic (FM) ordering, accompanied by a progressive reduction in N\'eel temperature. The $\mathrm{CuV}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$ manifests characteristics of a quasi-2D Heisenberg FM, exhibiting weak magnetic anisotropy and weak interlayer FM interactions. Dielectric characterization reveals that V substitution suppresses the antiferroelectric (AFE) ground state (space group $\mathit{Pc}$) of pristine $\mathrm{CuCr}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$, inducing a paraelectric state (space group C2/$c$) with enhanced dielectric relaxation and polar fluctuations across characteristic temperature ranges. Strikingly, a pronounced magnetodielectric response emerges near saturation fields (${H}_{s}$) in V-doped AFM compositions. Through Landau free energy analysis, we establish that the quadratic coupling between the FM order parameter ($M$), AFM order parameter ($A$), and polarization ($P$) plays a key role in mediating the observed magnetodielectric phenomena.