Magnetic and magneto-optical quenching in (Mn²⁺, Sr²⁺) metaphosphate glasses

Transition metal ions such as Mn²⁺, Fe²⁺, or Co²⁺ provide an interesting alternative to rare earth dopants in optically active glasses. In terms of their magneto-optical properties, they are not yet very well exploited. Here, we report on the effect of Mn²⁺ on Faraday rotation in a metaphosphate glass matrix along the join Mn_xSr_1-x(PO₃)₂ with x = 0...1. Mn²⁺ shows small optical extinction in the visible spectral range and, compared to other transition metal ions, a high effective magnetic moment. At high Mn- levels, however, the magneto-optical activity of Mn²⁺ is strongly quenched due to ionic clustering. The magnetic properties of the heavily Mn²⁺-loaded phosphate matrix are dominated by a superexchange interaction in the Mn²⁺-O-Mn²⁺ bridge with antiparallel spin alignment between Mn²⁺ and O^2- species. The apparent paramagnetic potential of Mn²⁺ species can therefore not be exploited at room temperature.