Limited Ferromagnetic Interactions in Monolayers of MPS3(M = Mnand Ni)

We present a systematic study of the electronic and magneticproperties of two-dimensional ordered alloys, consisting of two representativehosts (MnPS3and NiPS3) of transition metal phosphorus trichalcogenidesdoped with 3d elements. For both hosts, our DFT +Ucalculations are able toqualitatively reproduce the ratios and signs of all experimentally observedmagnetic couplings. The relative strength of all antiferromagnetic exchangecouplings, both in MnPS3and in NiPS3, can successfully be explained usingan effective direct exchange model: it reveals that the third-neighbor exchangedominates in NiPS3due to thefilling of the t2gsubshell, whereas for MnPS3,thefirst-neighbor exchange prevails, owing to the presence of the t2gmagnetism. On the other hand, the nearest neighborferromagnetic coupling in NiPS3can only be explained using a more complex superexchange model and is (also) largely triggered bythe absence of the t2gmagnetism. For the doped systems, the DFT +Ucalculations revealed that magnetic impurities do not affectthe magnetic ordering observed in the pure phases, and thus, in general in these systems, ferromagnetism may not be easily inducedby such a kind of elemental doping. However, unlike for the hosts, thefirst and second (dopant-host) exchange couplings are ofsimilar order of magnitude. This leads to frustration in the case of antiferromagnetic coupling and may be one of the reasons of theobserved lower magnetic ordering temperature of the doped systems.