An e.p.r. study of vacancy-impurity association in MgO

Paramagnetic resonance measurements have been made at X and Q bands on an axially symmetric spectrum of Fe 3+ in MgO. The tetragonal symmetry around the Fe 3+ ions arises from the presence of next nearest neighbour vacancies along a (100) axis. The orientation dependence of twelve transitions at X and Q band frequencies is found to be consistent with a spin Hamiltonian of the form, H=g// beta B z S z +g perpendicular to beta (B x S x +B y S y )+ D 3/O 0 2 + a- 120/(O 0 4 +5O 4 4 ) with D=+0.470 cm -1 , a=0.00262 cm -1 , g//=2.0026 and g perpendicular to =2.0037.