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 m easure the properties of materials. We present the details of an apparatus that extend these tunnel diode techniques to measure the properties of mate rials 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 th e radio frequency fields determine which property is measured. Our major in novations are to stabilize the tunnel diode oscillator during a magnet puls e by using compensated coils in the tank circuit and the development of two methods, one digital and one analog, to measure the frequency and amplitud e shifts in the oscillator during the short (10 s of ms) magnet pulse. We i llustrate the power of this new measurement method by showing preliminary r esults of the superconducting transition and the Shubnikov-de Haas effect i n the organic conductor kappa-(ET)(2)Cu(NCS)(2). The Shubnikov-de Haas effe ct shows particularly high amplitude oscillations due to magnetic breakdown orbits. (C) 2000 American Institute of Physics. [S0034-6748(00)01912-2].