Characterization of Mn2+ Doped Ammonium Hydrogen Oxalate Hemihydrate Single Crystals Using K-Band Electron Paramagnetic Resonance

Abstract

Ammonium hydrogen oxalate hemihydrate single crystals doped with Mn2+ ions have been studied at K-band electron paramagnetic resonance. Mn2+ ions enter the lattice substitutioanlly and give two equivalent magnetic sites. The spectra are very complex at ordinary orientation of the magnetic field; however they are similar and resoluble at the special directions corresponding to two principal Z-axes of the two magnetically equivalent sites of Mn2+ ions. Along the X crystal-field axis, which is the same for the two sites, spectrum is very simple and the direction is found to be parallel to the b crystal axis. The parameters describing the spectrum observed at room temperature are D = -135(1) mT, E = 4.0(14) mT, a = 1.0(2) mT, g(x) = 2.0006(4), g(y) = 2.0012(4), g(z) = 1.9947(2), A(x) = -9.32(20) mT, A(y) = -9.22(20)mT, and A(z) = -9.32(20) mT. These parameters were found from exact diagonalization of the spin Hamiltonian. The splitting of the forbidden doublets are calculated to fourth order perturbation theory and the value obtained for the nuclear quadruple coupling constant is Q' = -0.022 mT. Relatively large magnitude of D value and the small E value suggest that crystalline electric field is slightly distorted from tetragonal towards rhombic symmetry.