  A sensor for thermal and thermodynamic measurements of small magnetic systems
have been designed and built. It is based on a 5&mu;m-thick suspended polymer
membrane, which has a very low heat capacity (&asymp; 10-6 J/K at nitrogen
temperature), and on which a heater and a highly sensitive thermometer are
deposited. The sensor properties have been characterized as a function of
temperature and frequency. Energy exchanges as small as 1 picojoule (10-12
Joule) were detected in the 40K- 300K temperature range. Such values correspond
to those required for measuring the thermal signatures occurring during
magnetization reversal in very thin samples (typically 10 nm thick), which
would be deposited on the membrane. It is expected that this method will
constitute a powerful tool in view of analyzing magnetization reversal
processes in magnetic nanosystems, e.g. exhibiting the exchange-spring and
exchange-bias phenomena.
