Measuring radio frequency properties of materials in pulsed magnetic fields
T. Coffey, Z. Bayindir, J. F. DeCarolis, M. Bennett, G. Esper, and C. C. Agosta, "Measuring radio frequency properties of materials in pulsed magnetic fields with a tunnel diode oscillator," Review of Scientific Instruments, Vol. 71, No. 12 (December 2000), 4600-4606.
Abstract
Tunnel diode oscillators have been used in many types of experiments that measure the properties
of materials. We present the details of an apparatus that extend these tunnel diode techniques to
measure the properties of materials in pulsed magnetic fields. In the most common version of this
method, a sample is placed in the inductor of a small rf tank circuit powered by a tunnel diode and
the conductivity, magnetization, or penetration depth is measured. We explain in this article how the
sample and configuration of the radio frequency fields determine which property is measured. Our
major innovations are to stabilize the tunnel diode oscillator during a magnet pulse by using
compensated coils in the tank circuit and the development of two methods, one digital and one
analog, to measure the frequency and amplitude shifts in the oscillator during the short ~10 s of ms!
magnet pulse. We illustrate the power of this new measurement method by showing preliminary
results of the superconducting transition and the Shubnikov–de Haas effect in the organic conductor
k-~ET!2Cu~NCS!2 . The Shubnikov–de Haas effect shows particularly high amplitude oscillations
due to magnetic breakdown orbits.
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