A new method for direct rf power absorption studies in CMR materials and high T_c superconductors

TL;DR

This paper presents a novel apparatus for direct rf power absorption measurements in CMR and high T_c superconductors, enabling precise, automated analysis across a wide temperature and magnetic field range.

Contribution

The paper introduces a new, sensitive, and automated measurement system for direct rf power absorption in small CMR and superconducting samples, integrating with cryogenic equipment.

Findings

Successfully measured power absorption in La_0.7 Sr_0.3 MnO_3 and YBCO samples.

Achieved high sensitivity with a signal-to-noise ratio of 10:1.

Demonstrated system operation over 1 MHz to 25 MHz and 4.2 K to 400 K.

Abstract

The design, fabrication and performance of an apparatus for the measurement of direct rf power absorption in colossal magnetoresistive (CMR) and superconducting samples are described. The system consists of a self-resonant LC tank circuit of an oscillator driven by a NOT logic gate. The samples under investigation are placed in the core of the coil forming the inductance L and the absorbed power is determined from the measured change in the current supplied to the oscillator circuit. A customized low temperature insert is used to integrate the experiment with a commercial Oxford Instruments cryostat and temperature controller. The oscillator working in the rf range between 1 MHz to 25 MHz is built around an IC 74LS04. The temperature can be varied from 4.2 to 400 K and the magnetic field from 0 to 1.4 T. The apparatus is capable of measuring direct power absorption in CMR and superconducting samples of volume as small as 1/1000 cm^3 with a signal to noise ratio of 10:1. Further increase in the sensitivity can be obtained by summing the results of repeated measurements obtained at a given temperature. The system performance is evaluated by measuring the absorbed power in La_0.7 Sr_0.3 MnO_3 (LSMO) CMR manganite samples and superconducting Y Ba_2 Cu_3 O_7 (YBCO) samples at different rf frequencies. All operations during the measurements are automated using a computer with a menu-driven software system, user input being required only for the initiation of the measurement sequence.