Abstract
To reduce the magnetic field amplitude required to orient guanine crystal plates, we have attached magnetic nanoparticles to these guanine crystal plates. Fe2O3 nanoparticles are mixed with the guanine crystal plates, which are dispersed in water. Observation by optical microscopy confirmed that the large particles, which are nanoparticle aggregates, attach preferentially to the side edges of the guanine crystal plates. The individual crystal plate surfaces show clear, undisturbed light interference patterns, which mean that each plate’s optical properties have been maintained. The magnetic orientation experiments of these guanine crystal plates with different numbers of optically observed particles are conducted under both in-plane and vertical magnetic fields. The positions of the attached particles do not change, even when the magnetic field is applied. In these experiment, it was difficult to align the crystal direction with the magnetic field direction because the magnetic orientation characteristics are strongly affected by the positions and numbers of the attached particles. However, in-plane rotation and an increased tilt angle are achieved for the guanine crystal plates using magnetic fields of several millitesla.
Highlights
Biogenic guanine crystals are receiving significant attention for use as bio-reflectors because of their unique optical properties e.g., high reflectivity.1,2 Guanine crystal plates are magnetically aligned in water suspensions and this allows these plates to vary their light scattering states dynamically using magnetic fields.3–7 From this viewpoint, the guanine crystal plate is one of the most promising biogenic materials for micro-optical device applications as a bio-reflector
We have reported that deposition of a ferromagnetic thin film on a guanine crystal plate is quite effective in reducing the magnetic field required for orientation
We examine the combination of Fe2O3 nanoparticles with goldfish guanine crystal plates for magnetic orientation applications while maintaining the light transparency of the plate
Summary
Biogenic guanine crystals are receiving significant attention for use as bio-reflectors because of their unique optical properties e.g., high reflectivity. Guanine crystal plates are magnetically aligned in water suspensions and this allows these plates to vary their light scattering states dynamically using magnetic fields. From this viewpoint, the guanine crystal plate is one of the most promising biogenic materials for micro-optical device applications as a bio-reflector. It has been reported previously that light and dark stripe patterns caused by this optical interference effect were observed on the broadest surface of these crystal plates.. It has been reported previously that light and dark stripe patterns caused by this optical interference effect were observed on the broadest surface of these crystal plates.5,16 It was found that the field amplitude required for magnetic orientation was almost same as that needed for a guanine crystal that was entirely covered by the permalloy film, the in-plane field rotation response was quite slow This indicates that partial deposition of the ferromagnetic film or attachment of magnetic beads could be useful in reducing the magnetic field amplitude required for guanine crystal plate orientation without impairing the plate’s optical transparency. Experiments are conducted to determine the guanine crystal plate motion under in-plane and vertical magnetic fields
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