296
D. Passeri et al.
cells using magnetic NPs and determined the content and spatial distribution of
intracellular iron. Passeri et al. [50] reported the labeling of leukemic cells using
folic acid-coated core-shell superparamagnetic NPs in order to detect the presence
of folate receptors on the surface of the cell membrane using MFM. MFM was also
used by Reggente el at. [79] to confirm the presence of magnetite NPs internalized
in microglial cells from mice cerebral cortices. Recently, Kim et al. [80] reported the
used of MFM to analyze two breast cancer cell lines, MCF-7 and SK-BR-3, targeted
with antibody conjugated magnetic NPs and demonstrated the capability of their
MFM method to subtype cancer cells.
12.3.3 Manipulation
As previously discussed, since its invention, MFM has found larger and larger application in the world of magnetic micro- and nanomaterials as a powerful qualitative
and, more recently, quantitative magnetic characterization technique. Nevertheless,
the capability of applying and detecting magnetic forces at the nanoscale make MFM
a powerful tool potentially applicable, not only for magnetic measurements, but also
for magnetic and mechanical manipulation.
12.3.3.1 Magnetic Manipulation by MFM
While scanning the sample of interest, the magnetized MFM probe with its magnetic
stray field can induce significant changes in the magnetization state of the sample,
especially in case of soft magnetic materials (i.e., H c < H tip where H c is the coercivity of the sample and H tip is the magnetic field generated by the tip). In case
of multidomain ferromagnetic materials, slight changes in the configuration of the
domains structure can be observed, while soft magnetic nanomaterials, e.g., singledomain ferro- and superpara-magnetic nanoparticles, could even exhibit a complete
reversal of the magnetic moment [81–83]. When MFM technique needs to be used
for the imaging of the magnetization state or for the quantitative measurement of
the magnetic properties of the sample in certain conditions, this phenomenon is a
negative effect which has to be quantified and carefully taken into account. Nevertheless, the same phenomenon can be positively used for active, controlled magnetic
manipulation of nanofeatures and exploited, for example, for writing and reading
nanostructured magnetic logic devices. The possibility of using the MFM tip to
locally write a magnetic bit in patterned magnetic disks has been demonstrated for
the first time in 90’s, i.e., at the beginning of the application of MFM technique
for recording industry [84, 85], but has never been fully exploited. The prerequisite
for the writing process is that the effective tip stray field (H tip ) must be larger than
the switching field of the particle (H c ) [84], while reading is possible only if the
magnetization state of the bit is not varied during the scanning, i.e., if the tip stray
field is significantly lower than the coercive field of the particle H tip H c . In the
D. Passeri et al.
cells using magnetic NPs and determined the content and spatial distribution of
intracellular iron. Passeri et al. [50] reported the labeling of leukemic cells using
folic acid-coated core-shell superparamagnetic NPs in order to detect the presence
of folate receptors on the surface of the cell membrane using MFM. MFM was also
used by Reggente el at. [79] to confirm the presence of magnetite NPs internalized
in microglial cells from mice cerebral cortices. Recently, Kim et al. [80] reported the
used of MFM to analyze two breast cancer cell lines, MCF-7 and SK-BR-3, targeted
with antibody conjugated magnetic NPs and demonstrated the capability of their
MFM method to subtype cancer cells.
12.3.3 Manipulation
As previously discussed, since its invention, MFM has found larger and larger application in the world of magnetic micro- and nanomaterials as a powerful qualitative
and, more recently, quantitative magnetic characterization technique. Nevertheless,
the capability of applying and detecting magnetic forces at the nanoscale make MFM
a powerful tool potentially applicable, not only for magnetic measurements, but also
for magnetic and mechanical manipulation.
12.3.3.1 Magnetic Manipulation by MFM
While scanning the sample of interest, the magnetized MFM probe with its magnetic
stray field can induce significant changes in the magnetization state of the sample,
especially in case of soft magnetic materials (i.e., H c < H tip where H c is the coercivity of the sample and H tip is the magnetic field generated by the tip). In case
of multidomain ferromagnetic materials, slight changes in the configuration of the
domains structure can be observed, while soft magnetic nanomaterials, e.g., singledomain ferro- and superpara-magnetic nanoparticles, could even exhibit a complete
reversal of the magnetic moment [81–83]. When MFM technique needs to be used
for the imaging of the magnetization state or for the quantitative measurement of
the magnetic properties of the sample in certain conditions, this phenomenon is a
negative effect which has to be quantified and carefully taken into account. Nevertheless, the same phenomenon can be positively used for active, controlled magnetic
manipulation of nanofeatures and exploited, for example, for writing and reading
nanostructured magnetic logic devices. The possibility of using the MFM tip to
locally write a magnetic bit in patterned magnetic disks has been demonstrated for
the first time in 90’s, i.e., at the beginning of the application of MFM technique
for recording industry [84, 85], but has never been fully exploited. The prerequisite
for the writing process is that the effective tip stray field (H tip ) must be larger than
the switching field of the particle (H c ) [84], while reading is possible only if the
magnetization state of the bit is not varied during the scanning, i.e., if the tip stray
field is significantly lower than the coercive field of the particle H tip H c . In the