Hydroxide Semiconductors: New Series of van der Waals Magnets*

Electronic memory storage devices utilize different magnetic configurations for data storage. Among potential magnetic systems, antiferromagnetically (AFM) oriented systems possess timescales of magnetization faster than ferromagnetic (FM) ones, leading to more efficient operations. Vast efforts have been devoted to explore the 2D FM and AFM semiconducting materials in recent years for their usage in MRAM devices. With the help of first-principles calculations using GGA-PBE functional with vdW correction, we have predicted a new series of 2D magnetic transition metal hydroxide semiconductors X(OH)2 (X= Mn, Fe, Co Ni). We have explored the layer-dependent magnetic properties and the formation as well as exfoliation energies of the corresponding 2D monolayers. The exfoliation energies for monolayers of Mn, Fe, Co and Ni hydroxides are 9.51, 2.97, 8.62, and 7.19 meV/Å2 respectively.  The spin-polarized electronic structures of bulk and monolayer have been calculated to investigate their in-plane and out-of-plane lowest-energy magnetic configurations. All of these systems are observed to have a wide bandgap in their bulk state and stabilize in the collinear AFM state having A-type, G-type, C-type and A-type configurations for Mn, Fe, Co and Ni hydroxides respectively. There are band gap crossover transitions when thickness of the systems is reduced from bulk to monolayer. The magnetic phonon dispersion shows that the bulk systems are devoid of any structural instabilities.