Single crystal synthesis and properties of the two-dimensional van der Waals frustrated magnets, Mn2In2Se5 and Mn2Ga2S5

Abstract

There has been considerable interest in the search and design of two-dimensional (2D) van der Waals (vdW) compounds with exotic magnetic behavior. Here we establish the growth of phase pure crystals of Mn₂In₂Se₅ and Mn₂Ga₂S₅ and evaluate their structural, physical, and magnetic properties. These 2D vdW phases consist of double-octahedral thick Mn(S/Se)₆ layers capped by InSe₄ or GaS₄ tetrahedra. Transmission electron microscopy confirms phase purity with the absence of impurity intergrowths of other closely related 2D vdW phases including Mn(In/Ga)₂(Se/S)₄ or In₄Se₃. Optical absorption measurements indicate these compounds have indirect band gaps of 1.33 and 1.58 eV, respectively. We also establish the Raman signatures for both compounds. Mn₂In₂Se₅ and Mn₂Ga₂S₅ are significantly frustrated magnetic materials due to the competing magnetic interactions in this double-thick triangular arrangement of metal atoms. They have magnetic transition temperatures of 7 and 13 K, respectively, compared to Weiss constants of −198 and −340 K, respectively. AC susceptibility experiments indicate that both Mn₂In₂Se₅ and Mn₂Ga₂S₅ exhibit significant spin glass character. The significant magnetic frustration makes these materials unique 2D magnetic vdW building blocks.