Thin film microcalorimeter for heat capacity measurements ... - Physics

1844 Rev. Sci. Instrum., Vol. 73, No. 4, April 2002 Zink et al.
fields, lead to the consideration of our microcalorimeter technology
as a solution for the measurement of specific heats of
any small samples in fields up to 30 T and beyond. In these
types of measurements, the ability to rely on thermal conductance
values measured in zero field means only need be
measured in high field. Because the magnetoresistance of the
thermometers has no effect on the tau measurement, the thermometers
need not be calibrated in field. These facts save
valuable high field data acquisition time. There are yet many
challeges to adapting these microcalorimeters for use in very
high field systems, including the demands of space in small
magnet bores, assuring thermal stability of the calorimeter,
and measuring the impact of the thermometer’s magnetoresistance
on pulsed field measurements.
ACKNOWLEDGMENTS
The authors would like to thank Ami Berkowitz for the
use of the superconducting magnet system and Etienne Janod
for his work on the zero field experiment, as well as the NSF
DMR 9705300 and the Swiss National Fund for Scientific
Research for providing funding for this work.
FIG. 6. a Time constant as a function of temperature in magnetic fields
up to 8 T for a device with a 4000-Å-thick film sample of a-Gd 0.07 Si 0.93 .
The small shifts in are the signature of the field dependent specific heat of
this spin glass. The inset shows the same measurement from 2–80 K. The
large upturn in below 15 K is due to the large low temperature specific
heat of a-Gd x Si 1x . b The resulting heat capacity of this device. The
dotted line indicates the field independent contribution of the addenda,
which is 1% of the total specific heat at low T.
V. OUTLOOK-HIGH FIELD MEASUREMENTS
We have demonstrated that our membrane microcalorimeter
is an effective tool for measuring specific heat of thinfilm
and other small samples from 2–300 K in applied dc
magnetic fields up to 8 T. These results, particularly the reproducibility
of the thermal conductance in various magnetic
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