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Active Learning and Research
Active Learning and Research
Physicist Chuck Agosta and the students in his research lab study how a material's ability to conduct electricity is affected by changes in temperature, pressure and magnetic field.

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.

Full text of this article can be accessed here or here. Copyright (2000) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.

 

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