The magnetic ordering of graphite grains and an experimental application to grain alignment

The temperature dependence of diamagnetic grain orientation is reported for the first time concerning micron-sized graphite samples. An experimental method was developed for the purpose of studying the mechanism of interstellar grain alignment. The experiment was carried out in the temperature range from room temperature to 180 K, using ethanol as the suspending medium. The field of full orientation H-S decreased from 380 G to 260 G as the temperature decreased from room temperature to 180 K. The average sizes of the samples were 2.5 +/- 0.2 mu m and 3.8 +/- 0.2 mu m in diameter, and the thickness was 0.3 +/- 0.2 mu m. This temperature dependence of H-S agrees with a theoretical relation, which was derived from the theory of the Boltzmann distribution of suspended particles. A quantitative consistency in applying the conventional theory on interstellar grain alignment has not yet been achieved for the dense region, such as molecular clouds. The possibility of applying a diamagnetic-orientation experiment to the mechanism of interstellar grain alignment is discussed. The method for observing grain alignment established in the present work, can be applied for a quantitative evaluation of the star-light polarization mechanism.