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IMPROVEMENT OF REPRODUCIBILITY OF MAGNETIC MOMENT DETECTED BY A SQUID MAGNETOMETER THROUGH RADIAL OFFSET MEASUREMENT ON A YIG SPHERE

Published

Author(s)

Cindi L. Dennis, Robert D. Shull, Nobuhiro Matsumoto

Abstract

We report here on the reproducibility of measurements on a commercial SQUID Magnetometer of two different yttrium iron garnet (YIG) spheres, both having a diameter of 1 mm: (1) the NIST magnetic moment standard reference material (SRM) and (2) a commercial sample. It has been suggested that rotating the sample rod around its axis can move the sample center towards the center of the second-gradiometer coil. The observed value of the magnetic moment will be theoretically a minimum when the radial offset is zero and this value will increase in a “quadratic” manner with the radial offset. When the magnetic moment of the SRM was repeatedly measured as a function of rotation angle ϕ from 0o to 360o, we observed a sinusoidal variation in the measured values. The radial offset dependence of the observed magnetic moment was experimentally confirmed by measurements of the commercial sphere placed in a hole in several cylindrical PTFE containers, wherein the distance between the center of the hole and the center of the container was r. The r dependence of the minimum from each ϕ-dependent measurement series is qualitatively consistent with the theoretical curve. When the ϕ-dependent measurements for the SRM in a capsule were repeated 12 times over 21 months, the relative standard deviation of the minimums improved up to 0.1%. Knowledge of these facts will be necessary for accurate measurement of the magnetic moment of other sample forms (e.g., powders).
Citation
IEEE Transactions on Magnetics

Keywords

SQUID, reproducibility, YIG, calibration
Created September 19, 2018, Updated February 26, 2020