Low temperature dielectric properties of 88Sr48TiO3

It is well established that the behavior of amorphous solids at low temperatures is governed by atomic two-level tunneling systems with properties as detailed in the phenomenological tunneling model. However, this genuine tunneling model fails to explain the recently measured magnetic field dependence of the low temperature dielectric properties of glasses. Extensions of the tunneling model that include a coupling of the lateral motion of the atoms to the orientation of their nuclear quadrupole moment could explain at least some of the observed magnetic field effects. In our studies, we try to directly demonstrate this idea by comparing the dielectric behavior of SrTiO3-ceramics made of isotopes of natural abundance with that of samples enriched with the isotopes 88Sr and 48Ti which have no nuclear quadrupole moment. In contrast to the expectation, the magnetic field effects of the dielectric constant of 88Sr48TiO3 were not smaller but even 4.5 times larger than those of SrTiO3 with natural components. SQUID-magnetometer measurements revealed that our 88Sr48TiO3-material contains about 6 times more ferromagnetic and two orders of magnitude more paramagnetic impurities than our natural SrTiO3. Although ruled out by other authors, this again rises the question whether the sensitivity to magnetic fields of the dielectric properties of glasses at low temperatures is caused by magnetic impurities.