12 Magnetic Force Microscopy and Magnetic …
297
first works regarding the use of MFM for writing and reading processes, it has been
demonstrated that writing and reading process can be performed using two MFM
tips-a writing tip with a large magnetic moment and a reading tip with a very small
magnetic moment [84]. Also, a method for recording and erasing using a MFM tip
and the help of an external variable magnetic field has been proposed. In this method,
writing is performed with the MFM tip into contact with the sample and by applying
an external magnetic field parallel to the tip stray field; erasing is performed at a large
tip-sample separation, while applying an external field antiparallel to the tip stray
field [85]. The application of recent advances in the development of MFM technique
could allow the complete exploiting of MFM as a magnetic manipulation method. As
an example, a possible way to perform reading and writing processes has been more
recently proposed. A suitable MFM can be used to read the magnetic-moment states
of a particle at a large tip-particle separation, while it can be used for writing at a
smaller tip-sample separation, exploiting its higher magnetic stray field. This method
has been demonstrated to be effective for the control of the magnetic moment state of
a single particle [86] and could be applied for writing input to magnetic logic devices.
Furthermore, the recently developed capability of in situ controlling the magnetization state of the MFM probe by CM-MFM technique could be also applied [15] for
magnetic manipulation purposes. Indeed, the writing process could be performed by
using a strongly magnetized probe, e.g. in its saturation magnetization state. Then,
the magnetic moment (and the corresponding stray field) of the probe could be opportunely decrease for reading by applying to the probe an appropriate ‘demagnetizing’
magnetic field. Recent developments in AFM instrumentation make the technique
potentially scalable. Indeed, the operation of more than a thousand atomic force
microscopes in parallel has recently been demonstrated [87].
12.3.3.2 Mechanical Manipulation by MFM
The growing interest in fabrication of nanostructures in several technology fields
push researchers to look for new advanced fabrication methods with control and
resolution at the nanometer scale. Beside imaging and physical characterization,
SPM techniques, have started to be used also for nanofabrication and mechanical
manipulation purposes, exploiting the high resolution and low forces control capabilities. As an example, local deposition of material has been obtained by using
a scanning tunneling microscopy (STM) tip [88–90]. Mechanical manipulation of
nanostructures is getting increasing interest in nanopattern fabrication and has been
demonstrated to be doable by using a standard AFM probe, which can be used to push
or slide with controllable force the nanostructures of interest [91, 92]. The magnetic
stray field of the probe and the high resolution of MFM technique could be also
used for mechanical entrapment and manipulation of magnetic nanostructures for
nanofabrication purposes. Recently, Liu et al. [93] designed a helical capture path to
precisely manipulate magnetic (paramagnetic and superparamagnetic) nanoparticles
by a magnetized probe. The authors demonstrated the capability of MFM technique
to pick up and remove from the surfaces nanoparticles with diameters in the range
297
first works regarding the use of MFM for writing and reading processes, it has been
demonstrated that writing and reading process can be performed using two MFM
tips-a writing tip with a large magnetic moment and a reading tip with a very small
magnetic moment [84]. Also, a method for recording and erasing using a MFM tip
and the help of an external variable magnetic field has been proposed. In this method,
writing is performed with the MFM tip into contact with the sample and by applying
an external magnetic field parallel to the tip stray field; erasing is performed at a large
tip-sample separation, while applying an external field antiparallel to the tip stray
field [85]. The application of recent advances in the development of MFM technique
could allow the complete exploiting of MFM as a magnetic manipulation method. As
an example, a possible way to perform reading and writing processes has been more
recently proposed. A suitable MFM can be used to read the magnetic-moment states
of a particle at a large tip-particle separation, while it can be used for writing at a
smaller tip-sample separation, exploiting its higher magnetic stray field. This method
has been demonstrated to be effective for the control of the magnetic moment state of
a single particle [86] and could be applied for writing input to magnetic logic devices.
Furthermore, the recently developed capability of in situ controlling the magnetization state of the MFM probe by CM-MFM technique could be also applied [15] for
magnetic manipulation purposes. Indeed, the writing process could be performed by
using a strongly magnetized probe, e.g. in its saturation magnetization state. Then,
the magnetic moment (and the corresponding stray field) of the probe could be opportunely decrease for reading by applying to the probe an appropriate ‘demagnetizing’
magnetic field. Recent developments in AFM instrumentation make the technique
potentially scalable. Indeed, the operation of more than a thousand atomic force
microscopes in parallel has recently been demonstrated [87].
12.3.3.2 Mechanical Manipulation by MFM
The growing interest in fabrication of nanostructures in several technology fields
push researchers to look for new advanced fabrication methods with control and
resolution at the nanometer scale. Beside imaging and physical characterization,
SPM techniques, have started to be used also for nanofabrication and mechanical
manipulation purposes, exploiting the high resolution and low forces control capabilities. As an example, local deposition of material has been obtained by using
a scanning tunneling microscopy (STM) tip [88–90]. Mechanical manipulation of
nanostructures is getting increasing interest in nanopattern fabrication and has been
demonstrated to be doable by using a standard AFM probe, which can be used to push
or slide with controllable force the nanostructures of interest [91, 92]. The magnetic
stray field of the probe and the high resolution of MFM technique could be also
used for mechanical entrapment and manipulation of magnetic nanostructures for
nanofabrication purposes. Recently, Liu et al. [93] designed a helical capture path to
precisely manipulate magnetic (paramagnetic and superparamagnetic) nanoparticles
by a magnetized probe. The authors demonstrated the capability of MFM technique
to pick up and remove from the surfaces nanoparticles with diameters in the range