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.