Frequency-crossing phonon spectrometer techniques

Abstract

An ac technique for measuring magnetothermal conductivities using frequency crossing has been developed and shows a 13-fold increase in signal-to-noise ratio over the conventional dc technique. The ac technique employs low-frequency field modulation coupled with phase-sensitive detection and a 45-fold improvement in signal-to-noise ratio may be obtained by modulation over the half-width of the frequency crossing signal. A further increase of approximately 3 would be obtainable by increasing the modulation frequency and overcoming technical problems. The limit of detection and instrument revolution may be as low as 10 in. spins and a few megahertz, respectively.

Phonon spectroscopy

“…The practical details of thermal conductivity experiments are well established, and we refer the reader to Berman (1976). A number of refinements are necessary to take full advantage of the crossing technique, examples of which are found in the system developed by Wybourne et al (1979). To avoid magnetoresistance problems, thermometers were kept outside the magnetic field and attached to the sample by long copper wires.…”

Thermalization of a Phonon Spectrum Observed by Frequency Crossing

“…The temperature gradients (~7 mK/mm) were measured using pairs of contacts 4 mm apart each connected to 27-S2 Allen-Bradley carbon thermometers out of the main magnetic field as described elsewhere. 3 The pair nearer the interface is referred to as T n , the further pair T f . The field was swept through a crossing signal and the changes in the two temperature gradients were either plotted directly or stored in a signal averager (Datalab 4000).…”