5:15 PM - 6:30 PM
[PPS06-P20] Detection of Magnetic Anisotropy Using a Wide Field Area Produced by Ferrite Magnets
Keywords:Interstellar Medium, Magnetic Anisotropy
Polarization data in the visible and infrared region caused by partial dust alignment is commonly used to determine the direciton of magnetic field in various glactic area [1]. Observational studies has concluded that partially aligned silicate-grains can be he cause of the polarization. However, the physical mechanism of the aformentioned alignment in the dense region (i.e., the surrounding areas of the proto-planetary discs) leaves room for discussion, because dust and gas are in a thermo-dynamically equilibrium condition.In this study, it was assumed that partial alignment in the dense region was caused by anisotropy of magnetic susceptibility Δχ that was assigned tothe dust material [2]. In this case, the field-induced anisotropy energy induced in the dust should be larger than the Brownian energy (Uyeda et al., 1991, 2004a). Using a conventional torque method, value of Δχper unit mass was generally difficult to measure when its mass mwas below several milligrams [3], because mmeasurement of sample was difficult;note that the obtanable size of a single crystal is below sub-milimeter in dimaeter in many materials, and reliable Δχvalues aredifficut to obtain in these materials. Therefore a new method that was proposed and practicalized in which[A1] Δχwas determined from period of harmonic oscillation τ of stable axis of crystal with respect tomagnetic field B; here oscillation was induced by a field-induced anisotropyenergy½ΔχmB2, andτfollowed an equation
τ = 2π ( I/mΔχ)1/2|B|-1. (1)
whereIdenote moment of inertia of the crystal. It is seen that τis independent to min the above equation, andΔχ is determined form τ,I/m andBno matterhowsmallcrystalmay be, in condition that the oscillation is observable [3].
Here we introduced a pair of ferrite magnetic plate (10cm x 5cm x 1cm) was used to generate Bto increase the volume of homogeneous field area with respect to previous researches [3]. Accordingly, the mm-size sample released in μgarea was allowed to translate in a wide sperical area of ~3 cm in diameter during the observation of field-indused oscillation. The diameter of homogeneous area in the previos setup was less than ~1.5cm, and the sample frequently moved away from the homogeneous field area; success rate of τmeasurement was less than 20% due to this distervance. In the presentexperiment, Δχ values were obtained in milimetre sizecrystals of a paramagnetic chrorite and a diamagnetic graphite following the aforementioend propcedure. It is generally considerd that dynamic motions are not induced in diamagneitc and paramagnetic materials bya low field intensity produced by a ferrite magnet. The crystals used in the experiment were separated from bulk samples using a wire saw and a titanum knife. The sample was placed on a sample stage that was located at the the field center of two magnetic plates. A short microgravity condition (duration< 0.5s) was applyed to the setup by conducting a free fall [3][4].Shortly after the biginning of the free fall, the sample stageslowly lifted from its initial position, which was effectiveto release the small sample in a diffuse area.The rotational-oscillation of the samples were observed by a high-speed camera (ZWO ASI290MC) that was newly adopted in the experiment; the camera was capable to observe and presere the motion of the sample with a time resolution of 0.033 fps and a spatial resolution of 0.004 cm.
[1] for example, R. Spitzer Jr., Physical Processes in the Interstellar Medium (1978). [2] C. Uyeda, et. al., A & Ap (2001). [3] C. Uyeda et. al., (2010)J. Phys. Soc. Jpn.32, 164079. [4] Yokoi et al., Planet., Space Sci., 28, 094103.
[A1]Alternatively,
"in the sub-milligram range".
τ = 2π ( I/mΔχ)1/2|B|-1. (1)
whereIdenote moment of inertia of the crystal. It is seen that τis independent to min the above equation, andΔχ is determined form τ,I/m andBno matterhowsmallcrystalmay be, in condition that the oscillation is observable [3].
Here we introduced a pair of ferrite magnetic plate (10cm x 5cm x 1cm) was used to generate Bto increase the volume of homogeneous field area with respect to previous researches [3]. Accordingly, the mm-size sample released in μgarea was allowed to translate in a wide sperical area of ~3 cm in diameter during the observation of field-indused oscillation. The diameter of homogeneous area in the previos setup was less than ~1.5cm, and the sample frequently moved away from the homogeneous field area; success rate of τmeasurement was less than 20% due to this distervance. In the presentexperiment, Δχ values were obtained in milimetre sizecrystals of a paramagnetic chrorite and a diamagnetic graphite following the aforementioend propcedure. It is generally considerd that dynamic motions are not induced in diamagneitc and paramagnetic materials bya low field intensity produced by a ferrite magnet. The crystals used in the experiment were separated from bulk samples using a wire saw and a titanum knife. The sample was placed on a sample stage that was located at the the field center of two magnetic plates. A short microgravity condition (duration< 0.5s) was applyed to the setup by conducting a free fall [3][4].Shortly after the biginning of the free fall, the sample stageslowly lifted from its initial position, which was effectiveto release the small sample in a diffuse area.The rotational-oscillation of the samples were observed by a high-speed camera (ZWO ASI290MC) that was newly adopted in the experiment; the camera was capable to observe and presere the motion of the sample with a time resolution of 0.033 fps and a spatial resolution of 0.004 cm.
[1] for example, R. Spitzer Jr., Physical Processes in the Interstellar Medium (1978). [2] C. Uyeda, et. al., A & Ap (2001). [3] C. Uyeda et. al., (2010)J. Phys. Soc. Jpn.32, 164079. [4] Yokoi et al., Planet., Space Sci., 28, 094103.
[A1]Alternatively,
"in the sub-milligram range".