EPR study of exchange interactions of manganese ions in a CdGeAs2 matrix

The results of an EPR study of the CdGeAs₂ compound doped with 6 at % Mn are reported. The experimental data are analyzed under the assumption that magnetic centers of the following two types are formed in the system: Mn_Cd, Mn ions that replace Cd²⁺ and have spin S = 5/2, and Mn_Ge, Mn ions that replace Ge⁴⁺ and form the Mn²⁺ + 2p complex with two “heavy” holes with spin S = 1/2. The absence of signals from isolated centers and the Lorentzian shape of an absorption curve suggest a strong exchange narrowing of the spectrum and the extension of an isotropic exchange interaction involving Mn_Ge to distances much longer than the lattice parameter. It is found that the exchange interaction between Mn²⁺ + 2p complexes is ferromagnetic, and it is stronger than the characteristic superexchange interaction involving Mn_Cd centers by three to four orders of magnitude. The form of the temperature dependence of susceptibility obtained by the double integration of spectra is indicative of the formation of nanoscale regions, which weakly interact with each other, with ferromagnetically ordered Mn²⁺ + 2p complexes at ∼250 K.