Understanding the effect of chemical composition on the strength of magnetic interactions is key to the design of magnets with stronger exchange interactions. The magnetic divalent first-row transition metal (TM) thiocyanates are a class of chemically simple layered molecular frameworks. Here, we report two new members of the family, manganese (II) thiocyanate, Mn(NCS)2, and iron (II) thiocyanate, Fe(NCS)2. Using magnetic susceptibility measurements on these materials and on cobalt (II) thiocyanate and nickel (II) thiocyanate, Co(NCS)2 and Ni(NCS)2, respectively, we identify significantly stronger net antiferromagnetic interactions between the earlier TM ions-a decrease in the Weiss constant, \theta, from 29 K for Ni(NCS)2 to -115 K for Mn(NCS)2-a consequence of more diffuse 3d orbitals, increased orbital overlap and increasing numbers of unpaired t2g electrons. We elucidate the magnetic structures of these materials: Mn(NCS)2, Fe(NCS)2 and Co(NCS)2 order into the same antiferromagnetic commensurate ground state, whilst Ni(NCS)2 adopts a ground state structure consisting of ferromagnetically ordered layers stacked antiferromagnetically. We show that magnetic molecular frameworks with significantly stronger net exchange interactions can be constructed by using earlier TMs.
@article{arxiv.2003.03448,
title = {Strengthening the magnetic interactions in pseudobinary first-row transition metal thiocyanates, $\it{M}$(NCS)$_{2}$},
author = {Euan N. Bassey and Joseph A. M. Paddison and Evan N. Keyzer and Jeongjae Lee and Pascal Manuel and Ivan da Silva and Siân E. Dutton and Clare P. Grey and Matthew J. Cliffe},
journal= {arXiv preprint arXiv:2003.03448},
year = {2020}
}