EPR of ${\mathrm{Mn}}^{2+}$ -doped Zn ${\left({\mathrm{CH}}_3\mathrm{C}\mathrm{O}\mathrm{O}\right)}_2$ ·${2\mathrm{H}}_2$O, Mg ${\left({\mathrm{CH}}_3\mathrm{C}\mathrm{O}\mathrm{O}\right)}_2$ ·${4\mathrm{H}}_2$O, and Ni ${\left({\mathrm{CH}}_3\mathrm{C}\mathrm{O}\mathrm{O}\right)}_2$ ·${4\mathrm{H}}_2$O: ${\mathrm{Mn}}^{2+}$ -${\mathrm{Ni}}^{2+}$ exchange constant

$X$-band EPR measurements on ${\mathrm{Mn}}^{2+}$-doped single crystals of Zn ${\left({\mathrm{CH}}_3\mathrm{C}\mathrm{O}\mathrm{O}\right)}_2$ ·${2\mathrm{H}}_2$O, Mg ${\left({\mathrm{CH}}_3\mathrm{C}\mathrm{O}\mathrm{O}\right)}_2$ ·${4\mathrm{H}}_2$O, and Ni ${\left({\mathrm{CH}}_3\mathrm{C}\mathrm{O}\mathrm{O}\right)}_2$ ·${4\mathrm{H}}_2$O have been performed at room, liquid-nitrogen, and liquid-helium temperatures. The spin-Hamiltonian parameters are estimated by the use of a rigorous least-squares-fitting technique especially adapted to electron-nuclear spin-coupled systems, on a digital computer. The ${\mathrm{Mn}}^{2+}$-${\mathrm{Ni}}^{2+}$ exchange constant, using the shift of $g$ value in the paramagnetic nickel salt from that in the isostructural magnesium salt at liquid-helium temperature, has been determined to be 3.81 GHz.