  Generally, one has two strategies to achieve magnetic frustration: through
geometric means or interactions with different length scales. As the former
leads to much simpler theoretical treatments it is favored and so magnetic
sublattices with geometric frustration are sought after. One approach to
finding such lattices is to design them chemically by using non-magnetic linker
ligands. Here we report on the magnetic properties of one such family of
materials, the transition metal ($TM$) selenite hydrate compounds chemical
formula $TM_3$(SeO$_3$)$_3$H$_2$O . These materials link highly distorted
$TM$O$_6$ octahedra via non-magnetic [SeO$_3$]$^{2+}$ linkers. Using $TM$ = Mn,
Co and Ni we report on the structural effects of changing the $TM$ site and how
they may influence the magnetic structure. Using magnetic susceptibility and
neutron powder diffraction we identify low temperature magnetic transitions for
all three compounds characterized by the onset of long-range AFM order with
moderate frustration indexes. Consideration of the magnetic structures reveal
that the magnetic order is sensitive to the $TM$ site ion and is tunable as it
is changed - especially from Mn to Co - with changes in both the moment
direction and the ordering vector. Field dependent susceptibility and heat
capacity measurements reveal metamagnetic transitions in both
Mn$_3$(SeO$_3$)$_3$H$_2$O and Co$_3$(SeO$_3$)$_3$H$_2$O indicating nearby
magnetic ground states accessible under relatively small applied fields.
Density functional theory calculations broadly confirm these results, showing
both a sensitivity of the magnetic structure to the $TM$ and its local
environment. Although no spin liquid behavior is achieved, these results
suggest the fruitfulness of such synthesis philosophies and encourage future
work to engender higher frustration in these materials via doping, field,
pressure or larger linker ligands.
