Abstract Synthetic pyrite crystals doped with halogen (CI, Br) or manganese (Mn) were investigated by ESR at 78 K with an X-band spectrometer and a TE102 cavity with 100 kc field modulation. The crystals were preferably measured with the directions 〈100〉, 〈110〉, and 〈111〉 parallel to the static magnetic field HO. The ESR spectrum of Mn-doped crystals showed a sextet which can be explained by a spin-Hamiltonian for an electron spin S = 1/2 in interaction with the nuclear spin I = 5/2 of the Mn nucleus for axial symmetry. Due to the observed spin and due to the orientation of the paramagnetic centers the spectra were assigned to Mn2+ in the low spin state which resides on cation site in the FeS2, lattice. In halogen-doped crystals four pairs of lines can be interpreted by the interaction of the two isotopes of I = 3/2, 79Br, 81Br and 35Cl, 37Cl, respectively, with an electron spin S = 1/2. According to the observed symmetry of the ESR signals the paramagnetic centers can be explained as (S-X)2- radicals (X = CI, Br) which substitute for the (S2)2- dumb-bells of pyrite. All crystals evoked extremely narrow ESR lines, especially the halogen-doped crystals with linewidths down to 0.03 mT. Excellent agreement between measured and calculated spectra up to the finest details has been obtained.
ESR studies of superconducting cuprates: Low magnetic field effects at X-band and 300 MHz