Strong anisotropy in the mixed antiferromagnetic system Mn1−xFexPSe3

Abstract

We report the magnetic phase diagram of ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{PSe}}_{3}$, which represents a random magnet system of two antiferromagnetic systems with mixed spin, mixed spin anisotropies, mixed nearest-neighbor magnetic interactions, and mixed periodicities in their respective antiferromagnetic structure. Bulk samples of ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{PSe}}_{3}$ have been prepared and characterized phase pure by powder x-ray and neutron diffraction and x-ray fluorescence. Nature and extent of magnetically ordered state has been established using powder neutron diffraction, dc magnetic susceptibility, and heat capacity. Long-range magnetic ordering exists between $x=0.0$ and 0.25 (${\mathrm{MnPSe}}_{3}$ type) and between $x=0.875$ and 1 (${\mathrm{FePSe}}_{3}$ type). A short-range magnetic order with the existence of both ${\mathrm{MnPSe}}_{3}$- and ${\mathrm{FePSe}}_{3}$-type nanoclusters has been established between $x=0.25$ and 0.875. Irreversibility in dc magnetization measurements, also characterized by isothermal and thermoremanent magnetization measurements, suggest similarities to magnetic nanoparticles where uncompensated surface spins result in diverging thermoremanent and isothermal remanent magnetization responses, further reinforcing existence of magnetic nanoclusters or domains. A spin-glass state, observed in analogous ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{PS}}_{3}$, has been ruled out, and formation of nanoclusters exhibiting both ordering types results from unusually high anisotropy values. The effect of ligand contributions to the spin-orbit interactions has been suggested as a possible explanation for high $D$ values in these compounds.