Crystal growth and anisotropic magnetic properties of quasi-two-dimensional(Fe1−xNix)2P2S6

Abstract

We report the crystal growth by chemical vapor transport together with a thorough structural and magnetic characterization of the quasi-2D magnets ${({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x})}_{2}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$ with ${x}_{\text{Ni}}=\text{0,}\phantom{\rule{4.pt}{0ex}}\text{0.3,}\phantom{\rule{4.pt}{0ex}}\text{0.5,}\phantom{\rule{4.pt}{0ex}}\text{0.7,}\phantom{\rule{4.pt}{0ex}}\text{0.9}$, and 1. As-grown crystals exhibit a layered morphology with weak van der Waals interactions between layers parallel to the crystallographic $ab$ plane of the monoclinic structure in the space group $C2/m$ (No. 12). Magnetization measurements reveal an antiferromagnetic ground state for all grown crystals. In the ordered state, the magnetization along different crystallographic directions is in agreement with an Ising anisotropy for $0\ensuremath{\le}x\ensuremath{\le}0.9$ and only for ${\mathrm{Ni}}_{2}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$ a different behavior is observed which is in line with an anisotropic Heisenberg or $XXZ$ model description. This striking abrupt change of anisotropy at a critical Ni concentration is coupled to a change in the width of the maximum in the magnetization around ${T}_{\text{max}}$. Furthermore, all intermediate compounds $0<x\ensuremath{\le}0.9$ exhibit an anisotropic magnetization already in the paramagnetic state similar to the parent compound ${\mathrm{Fe}}_{2}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$.