SPECIFIC HEAT MEASUREMENT MODULE

The Cryogenic Limited miniature AC calorimeter is designed to measure the heat capacity of samples weighing as little as one microgram. The AC technique offers unsurpassed sensitivity combined with simplicity of operation.

The sample is mounted on to the calorimeter membrane using thermally conductive vacuum grease and placed in a closed cell with low-pressure exchange gas. The probe is inserted into the VTI through an airlock.

Key features:

Low amplitude of temperature oscillations giving excellent temperature resolution (typically 0.1K at 50K). This makes the technique ideally suited to investigations of narrow phase transitions.

Fast measurement. The frequency of the temperature modulation is of the order of 100 to 10 Hz so the effective time constant is in the range 0.1 to 1 seconds. This allows the heat capacity to be recorded as a function of continuously varying external parameters (temperature or field), through a phase transition.

High sensitivity: The sensitive element is manufactured using silicon-nitride membrane technology and sensors are calibrated over the entire range of temperature and magnetic fields of interest. The high sensitivity, around 1 nJ/K, allows studies of the small single crystals typical of novel materials.

Robustness and Durability: The membranes are strong and robust. With reasonable care the lifetime of a single sensor can span over tens of sample replacements. The system is offered with several spare sample cells; additional cells are readily available at reasonable cost.

Sample size: Ideally the lateral sample size should match the size of the miniature heater patterned on the membrane, which is approximately 100 x 200 microns. Using larger samples may reduce accuracy, although the qualitative features of the heat capacity will be resolved correctly.

Specific Heat Operating Parameters
Temperature range: 5 K to 300 K
Frequency of temperature modulation: 0.1 – 100Hz typical
Amplitude of temperature modulation: 0.01 – 0.1K
Typical sample dimensions:100 x 200 microns
Typical sample mass: 1 -10 microgram