Article |
Magnetic alignment experiment of fine graphite-crystals dispersed in He gas oriented to study alignment of crystalline-axes of nano-sized non-magnetic particles
Institute of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560, Japan
* To whom correspondence should be addressed. E-mail: uyeda{at}ess.sci.osaka-u.ac.jp
Abstract
The ensemble of nano-sized crystals is expected to attain additional physical properties when preferential alignments of certain crystal-axes are achieved by a magnetic field. The reduction of temperature T may realize alignment even if the mole number of the particle N and the diamagnetic anisotropy per mole (
)DIA are considerably small for the nano-sized diamagnetic oxides, since alignment proceeds by the balance between the energy of rotational Brownian motion and field-induced anisotropy energy. Alignment of various basic inorganic oxides such as gypsum, quartz, forsterite, KDP or calcite, having a size of 20 nm diameter, is expected to occur by a field intensity of 
50 T at T = 10 K; this intensity is presently available at a high magnetic-field laboratory. It is expected that the magnetic alignment of nano-sized particles can be observed by dispersing the particles in He gas, as achieved recently for micron-sized graphite crystals; a cryogenic liquid cannot be used as a dispersing medium. Measured ()DIA values accumulated for basic inorganic-oxides are explained quantitatively by assuming that individual bonding-orbital composing the material possesses a constant amount of diamagnetic anisotropy; hence the majority of diamagnetic nano-sized insulators are expected to show magnetic alignment at finite field intensity.
Keywords Magnetic alignment, graphite, He gas, nano-sized particles, diamagnetic anisotropy, low temperature
Received 17 September 2004, accepted 15 October 2004