Measuring radio frequency properties of materials in pulsed magnetic fields with a tunnel diode oscillator

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 kappa-(ET)(2)Cu(NCS)(2). The Shubnikov-de Haas effect shows particularly high amplitude oscillations due to magnetic breakdown orbits. (C) 2000 American Institute of Physics. [S0034-6748(00)01912-2].