Magnetization of a Diamagnetic Particle Measured From its Parabolic Movement Caused by Field-Gradient Force in Terrestrial Gravity

Diamagnetic susceptibility
$\chi _{\mathrm {DIA}}$
of a small particle is determined from its parabolic translation induced by a field gradient generated by a pair of neodymium magnet in normal gravity condition. Specifically,
$\chi _{\mathrm {DIA}}$
of a single particle is determined from the relationships between velocity
$v(x_{i})$
of particle and field intensity
$B(x_{i})$
that are observed at different positions
$x_{i}$
of a horizontal coordinate, without measuring mass
$m$
of particle. The method was based on a recent finding that the variance of acceleration observed between the translating particles induced in a common area of field gradient is uniquely determined by
$\chi _{\mathrm {DIA}}$
of material. Weak magnetic (i.e., diamagnetic and paramagnetic) materials were previously not considered to show translation by a low magnetic field produced by a permanent magnet. Using a conventional device, measurement of diamagnetic susceptibility
$\chi _{\mathrm {DIA}}$
generally requires a bulk sample that weight above
$\sim 1$
mg. In the new apparatus, the accuracy of obtained
$\chi _{\mathrm {DIA}}$
value was significantly improved by optimizing the field distribution of the magnetic circuit, thus decreasing the fluctuation of
$v(x_{i})$
values, and
$\chi _{\mathrm {DIA}}$
of a submillimetre-size sample is measurable with an uncertainty below
$5\times 10^{-7}$
emu/g. Approximate
$\chi _{\mathrm {DIA}}$
value of the translated particle is swiftly estimated from its position recovered on a collecting plate that is set at bottom of the translating area. Material identification of the translated particle is possible by collating the obtained
$\chi _{\mathrm {DIA}}$
value with a list of published data; unlike most conventional methods of chemical analysis, the identification is conducted without consuming the sample. Hence, the setup will extend as an effective technique of pre-treatment in analyzing a mixture of heterogeneous particles; such a technique is useful in various types of material exploration.