Highly sensitive parylene membrane-based ac-calorimeter for small mass magnetic samples.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Characterizing magnetic systems requires sensitive measurement tools.
• Low-frequency and low-temperature measurements present unique challenges.
• Existing calorimeters may lack the sensitivity for small mass magnetic systems.

Purpose of the Study:

• To design and fabricate a highly sensitive AC-calorimeter.
• To enable characterization of small mass magnetic systems at low frequencies and temperatures.
• To achieve high sensitivity for detecting small energy exchanges.

Main Methods:

• Microfabrication of a calorimetric cell using a parylene C membrane and NbN(x) thin films.
• Suspended structure design for minimal heat capacity and thermal link.
• Characterization of the calorimeter's performance as a function of frequency, temperature, and magnetic field.

Main Results:

• Achieved a highly sensitive AC-calorimeter with very low heat capacity addenda (microJ/K).
• Demonstrated a significantly reduced thermal link (<10^-8 W/K at 50 K).
• Successfully detected energy exchanges as small as 1 picoJoule and evidenced ferromagnetic phase transitions.

Conclusions:

• The developed AC-calorimeter is suitable for sensitive characterization of small magnetic systems.
• The microfabrication approach offers a pathway to highly isolated calorimetric systems.
• The device opens new possibilities for studying magnetic phase transitions at low frequencies.