Susceptibility of Diamagnetic Particles Measured in a Microgravity Using a Simple Double-Capsule System

Attempts to improve the accuracy in measuring diamagnetic susceptibility χ
_DIA
of a small particle are conducted by measuring its magnetic translation. In this study, accuracy improvement was pursued by two different experiments. First, translation of a particle was observed the under microgravity (
$\mu$
ɡ
) conditions produced by a simple double-capsule system that was developed to sufficiently reduce the residual gravity. In particular, gravity (
ɡ
) was reduced to a value below 2 × 10
⁻³
times the value of
ɡ
at sea level for 0.5 s by selecting the optimum material for the outer capsule. Furthermore, a simple technique to produce a time lag between the drop of the inner capsule considering the outer capsule was effective in minimizing the initial
ɡ
-vibration of the inner capsule. Preliminary experiments using this double-capsule system indicated that the typical error of χ
_DIA
was reduced by 80% (i.e., δχ
_DIA
 ≈ 2 × 10
⁻⁷
emu/g) when compared to that obtained in a previous study under
$\mu$
ɡ
conditions. Many phenomena studied in condensed matter physics are measured at time scales below 0.1 s, and the new
$\mu$
ɡ
system is effective when complete isolation of the sample from the measuring device is required, as realized in the χ
_DIA
measurements experiment reported in this letter. In another experiment, horizontal parabolic translation was conducted under normal gravity; here, translation was induced by a field-gradient force produced by a Nd-Fe-B magnetic circuit. The accuracy of χ
_DIA
obtained by field-induced translation was significantly improved by optimizing the field distribution of the magnetic circuit; a typical error of χ
_DIA
remained at a level of 5 × 10
⁻⁷
emu/g. Compared to the aforementioned double-capsule system, the compact apparatus operated under normal
ɡ
can be easily transported to various sites of material exploration to conduct preliminary χ
_DIA
measurement of test samples.