EPR ofMn2+-dopedNiSO4·7H2O andMgSO4·7H2O:Mn2+−Ni2+exchange constant

Abstract

$X$-band EPR measurements on ${\mathrm{Mn}}^{2+}$ -doped isostructural single crystals of paramagnetic ${\mathrm{NiSO}}_{4}$ \ifmmode\cdot\else\textperiodcentered\fi{} ${7\mathrm{H}}_{2}$O and diamagnetic ${\mathrm{MgSO}}_{4}$ \ifmmode\cdot\else\textperiodcentered\fi{} ${7\mathrm{H}}_{2}$O have been made at room, liquid-nitrogen, and liquid-helium temperatures. The spin-Hamiltonian parameters are evaluated from the data using a rigorous least-squares-fitting program suitable for electron-nuclear spin-coupled systems. Using the $g$ shift in the paramagnetic lattice from that in the diamagnetic lattice a value of 4.293 GHz for the ${\mathrm{Mn}}^{2+}$-${\mathrm{Ni}}^{2+}$ exchange constant in ${\mathrm{NiSO}}_{4}$ \ifmmode\cdot\else\textperiodcentered\fi{} ${7\mathrm{H}}_{2}$O is estimated. For ${\mathrm{NiSO}}_{4}$ \ifmmode\cdot\else\textperiodcentered\fi{} ${7\mathrm{H}}_{2}$O host the linewidths exhibit temperature and magnetic field dependence. The temperature dependence of the zero-field splitting parameter ${b}_{2}^{0}$ for both hosts is found to be linear, thus being explained as mainly due to the thermal expansion of the lattice.