Radio-frequency impedance measurements using a tunnel-diode oscillator technique

Abstract

A resonant method based on a tunnel-diode oscillator (TDO) for precision measurements of relative impedance changes in materials, is described. The system consists of an effective self-resonant LCtank circuit driven by a forward-biased tunnel diode operating in its negative resistance region. Samples under investigation are placed in the core of an inductive coil and impedance changes are determined directly from the measured shift in resonance frequency. A customized low temperature insert is used to integrate this experiment with a commercial Model 6000 Physical Property Measurement System (Quantum Design). Test measurements on a manganese-based perovskite sample exhibiting colossal magneto-resistance (CMR) indicate that this method is well suited to study the magneto-impedance in these materials.

Exchange bias effect in Au-Fe3O4nanocomposites

“…The TS has been a largely successful technique for directly probing magnetic anisotropy in assemblies of single domain particles. 28,29 This method measures the susceptibility by means of a perturbing alternating current field (H AC ) oriented perpendicular to a changing direct current (DC) magnetic field, H DC . In the theoretical paper on the transverse susceptibility of a Stoner Wohlfarth particle, Aharoni et al calculated that three singularities would be observed in the transverse susceptibility when H DC was scanned from positive to negative saturation.…”

Dynamic radio-frequency transverse susceptibility in magnetic nanoparticle systems

“…The measurements were done using a LC-tank resonator driven by a tunnel diode forward biased in its negative resistance region. This idea is the basis of the TDO measurement system whose circuit design and operation have been described elsewhere in detail [9]. The circuit is self-resonant with a typical resonance frequency around 5MHz.…”

“…To probe the dynamic transverse susceptibility in the radio-frequency range we employed a very sensitive method that we have recently developed [9]. Our experiments are based on a novel tunnel-diode oscillator (TDO) technique that combines the advantages of the precision afforded by resonance frequency measurements along with the transverse modulation principle.…”

Phase coexistence and magnetic anisotropy in polycrystalline and nanocrystalline LaMnO3+δ

“…The magnetic anisotropy and switching fields in the samples were probed by TS using a sensitive, self resonant tunnel diode oscillating (TDO) technique 11 with a resonant frequency of $20 MHz. The sample was placed in the inductance coil of the tank circuit integrated into the PPMS.…”