MICROWAVE PROPERTIES OF A RUTILE RESONATOR BETWEEN 2 AND 10 K

We report new microwave measurements of the anisotropic loss tangent a nd permittivity of rutile (TiO2) using well confined 'whispering galle ry' type modes of a shielded dielectric resonator. We report the first measurement of the two independent components of the loss tangent ten sor, as well as the lowest measurement yet of the total loss tangent o f 3.0 x 10(-8) parallel to the crystal c-axis and 1.5 x 10(-8) perpend icular to the c-axis, both measured at 3 K. We show that the mode freq uency dependence possesses two stationary points in the temperature ra nge 2-10 K and explain this dependence in terms of the competing effec ts of incidental paramagnetic impurities in the rutile, the variation of the rutile's permittivity with temperature and the thermal expansio n of the material. We give the first measurements of the anisotropic p ermittivity of rutile at low temperatures.