Biomedical Engineering Reference
In-Depth Information
of the substrate determines the morphology of the columnar structures and
this in turn has a profound influence on the magnetic properties. Nucleation
of Fe-Ni nanocolumns on a smooth silicon substrate was at random, while
that on a rough glass substrate was defined by irregularities on the substrate
surface. It has been found that magnetic interaction between nanocolumns
prepared on a silicon substrate was due to their small inter-column
separation. Well-separated nanocolumns on a glass substrate resulted in
exchange isolated magnetic domains.
The size, shape and distribution of nanocolumns can be tailored by
appropriately choosing the surface roughness of the substrate, which will
find potential applications in thin-film magnetism. In a technique for
measuring the magnetostriction in amorphous Fe-Ni thin film an optical
fiber long-period grating (LPG) was used. An LPG consists of a periodic
modification of the refractive index of the core of an optical fiber. For these
gratings, the energy typically couples from the fundamental guided mode to
the discrete forward-propagating cladding mode. When tensile stress is
applied to the optical fiber LPG the periodic spacing changes and reversibly
causes the coupling wavelength to shift. This provides a sensitive mechanism
to measure the stress/strain and also the magnetostriction of a material
attached to the fiber grating. Fe-Ni thin films were coated on a LPG. The
magnetostriction of the films was determined from the change in the peak
position of the attenuation band when a magnetic field was applied along
the axis of the fiber. Results indicate that LPGs in combination with Fe-Ni
thin films can act as a potential candidate in the field of magnetostrictive
sensors.
Magnetic fine particles of Fe-Co and Fe-Ni alloys encapsulated by
graphitic carbon (C) have been synthesized by annealing Fe 2 O 3 ,Co 3 O 4 and
NiO with carbon powders at 1273K in a nitrogen atmosphere. Saturation
magnetizations of the Fe-Co and Fe-Ni particles were 122-150 and 7.8-
105 A m 2 /kg, respectively. X-ray diffraction measurement showed that the
Fe-Co was composed of two phases with face-centered-cubic (fcc) and
body-centered-cubic (bcc) phases, while the Fe-Ni was only a fcc phase.
Lattice constants of both particles depended on their composition, which
suggested that they were alloys. This was confirmed by Mo¨ ssbauer
spectroscopy. Electron microscope images and electron energy loss spectro-
scope spectra revealed that these particles, with diameters of 100-200 nm,
were encapsulated by C layers with a thickness of several
￿ ￿ ￿ ￿ ￿ ￿
tens of
nanometers.
Magnetic nanomaterials, fabricated by various methods, have attracted a
great deal of attention for their technological applications, such as magnetic
storage media, sensors and magnetic random access memory (MRAM). In
these nanomaterials, each ferromagnetic region is a single domain in which
the magnetic spins are aligned in one direction. Thus every ferromagnetic
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