Microwave response near zero magnetic field in transition-metal-doped silicate glasses

A sharp microwave response centered at zero magnetic field was observed in manganese- and iron-doped Na2O-CaO-MgO-SiO2 glasses with phase opposite to the normal Mn+2 and Fe+3 paramagnetic signals. The response can be describe d as magneto-induced microwave conductivity in the dielectric glass that de rives from spin-dependent charge migration within the first coordination sp here of the paramagnetic ion. In contrast to the spin-polarized tunneling i n ferromagnets between different valence states of metals, the observed eff ect is due to spin-dependent tunneling that occurs in the vicinity of manga nese or iron in diluted paramagnetic systems. (C) 2000 American Institute o f Physics. [S0003-6951(00)02706-6].