Spin Hamiltonians and pair interactions of Co2+ in MgSiF6⋅6H2O, ZnSiF6⋅6H2O, and CoSiF6⋅6H2O

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Abstract
The spin‐Hamiltonian parameters including the orientation of the principal axes have been determined for the two ions in the monoclinic unit cell of the low temperature form of MgSiF6⋅6H2O. The principal values of the g tensor gzz=7.15, gyy=2.73, and gxx=2.17 are close to the values 6.85, 2.7, and 2.1 determined in this investigation for CoSiF6⋅6H2O which has a similar structure. Magnetic interactions determined from pair spectra in the Mg crystal appear to apply to the four nearest neighbor pairs in the monoclinic structure. The values of the pair interactions in the Mg crystal are quite consistent with the magnetic and thermal properties previously determined for CoSiF6⋅6H2O and with the electron paramagnetic resonance linewidths determined here. The magnetic interactions are vastly different for the nearest and the next nearest neighbor despite their almost identical distances, and the interactions of Co2+ pairs are much different for all neighbors in the rhombohedral host ZnSiF6⋅6H2O. It is suggested that these large variations are due to changes in the orientation of the water octahedra which affect the hydrogen bonding between neighboring octahedra.