Heat capacity measurements in high magnetic fields. J. B. Betts, A. Migliori, S. Riggs, F.F.Balakirev National High Magnetic Field laboratory @ Tallahassee & Los Alamos National Laboratory. Outline. Heat capacity measurement methods Cryogenics and probes Taking the data
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Heat capacity measurements in high magnetic fields
J. B. Betts, A. Migliori, S. Riggs, F.F.Balakirev
National High Magnetic Field laboratory @ Tallahassee & Los Alamos National Laboratory
Methods we use to measure heat capacity.
We use the same calorimeter setup for all three methods
Weak thermal link
Temperature controlled block
Thermometer (Cernox)
Sample
NiCr Heater
Heater
Sapphire platform
Thermometer
NiCr leads Silver
epoxy contacts
Sample platform
With integral heater and thermometer
Cp = Tau * kappa
Pros.
Cons.
Cp = Heater Power/(slope(W) – slope(C))
Pros.
Cons.
Cp = AC Heater Power/(2f(T[ac])
Cons.
Pros.
Temperature control & taking the data
Lockin Amplifier
Heat capacity platform
+

1KHz – 5KHz
Current resistor
Platform
Thermometer
Transformer
V
Platform
Heater
I
+

1KHz – 5KHz
Current resistor
Platform
Thermometer
Transformer
+
Platform
Heater

1Hz – 10Hz
Current resistor
Taking the data with the digital lockin
The hardware
Taking the data with the digital lockin
The software
Taking the data with the digital lockin
Second channel used to record heater voltage
Digital lockin setup for AC calorimetry
Variable sine out
5KHz
Current resistor
Platform
Thermometer
Transformer
+
Digitizer
50 Points/sine wave
Clock
250KHz
Thermometer RMS voltage
Digital lockin
Platform
Heater

5Hz
500 Points/sine wave
Current resistor
Thermometer 10Hz Pk–Pk voltage
Digital lockin
Fixed sine out
8 small Manganin leads, large open loop area
Good vibrational stability
4 small NiCr leads smaller open loop area
Very good vibrational stability