Paramagnetic tunneling systems and their contribution to the polarization echo in glasses

Startling magnetic effects on the spontaneous polarization echo in some silicate glasses at low and ultralow temperatures have been reported in the last decade or so. Though some progress in search of an explanation has been made by considering the nuclear quadrupole dephasing of tunneling particles, here we show that the effect of a magnetic field can be understood quantitatively by means of a special tunnel mechanism associated with paramagnetic impurities. For the Fe(3+)-, Cr(3+)-, and Nd(3+)-contaminated glasses we provide reasonable fits to the published data as a function of applied magnetic field and temperature.