Host spin–lattice relaxation narrowing in the EPR of Mn2+ in CoSO4⋅7H2O single crystals

Electron paramagnetic resonance (EPR) of Mn2+ doped in CoSO4⋅7H2O single crystals has been studied from 300 to 77 K and at ∼9.3 GHz. Two different types of crystals of CoSO4⋅7H2O have been obtained, which grow in two different temperature ranges about 298 K. The two forms exhibit different types of spectra: one form [to be referred to as CoSH(I)] shows two 30 line Mn2+ spectra with D=459×10−4 cm−1, ‖E‖=134×10−4 cm−1 and the other form [to be referred to as CoSH(II)] shows only a single 30 line spectrum with D=234×10−4 cm−1, ‖E‖=19 ×10−4 cm−1. The observation of resolved Mn2+ spectra at 300 K and its broadening on lowering the temperature in CoSO4⋅7H2O:Mn2+ crystals has been discussed in terms of ’’host spin–lattice relaxation narrowing.’’ The observed shift in the Mn2+ gz value from that in diamagnetic hosts is probably due to the Co2+ ions, which produce a local static magnetic field at the site of Mn2+ ions. From the observed linewidth in the EPR spectrum of Mn2+ in single crystals of CoSO4⋅7H2O the T1 of Co2+ in CoSO4⋅7H2O has been estimated to be ∼1.1×10−11 s.