The same Fe antidots film was magnetically characterized at room
temperature by F. Cebollada and F. Pigazo in the EUIT Telecomunicacion
UPM using a magnetooptic Kerr effect device.
The examined sample had diameter and interantidot
distance . The Kerr device is adapted to
measure the angular dependence of the
hysteresis loops and also the transverse initial susceptibility
(TS). This technique yields the effective anisotropy field of
a sample and consists of generating small amplitude magnetization
oscillations in a saturated sample by simultaneously applying a
large (saturating) DC field
-along either the e.a. or the
h.a.- and a small AC field ,
[Hoffmann 64]. The laser beam
was collimated to
. Due to the size of
lithographed area, this allows to measure independently the
demagnetization loops in the external Fe film and in the antidots
region (see Fig. 5.10).
Experimental geometry to measure Kerr signal in Fe antidot film in the
external region and in the antidots region.
Hysteresis loops measured in the continuous film and
antidots regions along the (a) easy and (b) hard axes. Measured in the
EUITT UPM by F. Pigazo and F. Cebollada.
Fig. 5.11 shows the hysteresis loops
to the antidots region and to the continuous film measured in the
film plane along the e.a (a) and the hardest in-plane axis (b) of
The measured coercivity is congruent with the result obtained by J.M.
Torres using AGFM, including the different values for the external and
the antidots region.
The TS measurements obtained in the array region along both the e.a.
in-plane h.a. (inset in Fig. 5.12)
anisotropy field close to
that, by considering the bulk Fe
magnetization value, corresponds to a first order anisotropy
constant value , very similar to the
corresponding bulk Fe magnetocrystalline anisotropy constant. The TS
results confirm that the patterning process preserves the original
four-fold symmetry but do
not show any increase of the anisotropy constant with respect to
that of the bulk Fe. This can be related to the fact that
the magnetization oscillations induced during the TS measurements do
not result in significant variations of the dipolar energy of the
moment structures at the antidots surfaces. As for
the angular dependence of the reversal process, the loops measured
in the antidot region with the field applied along a direction at an
respect to the Fe e.a. (Fig.
5.12 shows the loops measured at ; and ;) present two
irreversible jumps at fields
and , with the only
exceptions of those measured
along the e.a. ( ) and the in-plane h.a. ( ), which present a
single jump. Therefore, for these angles the total film magnetization
presents three jumps: two corresponding to the antidot region and the
other one to the non-lithographed film.
Fig. 5.13 shows the evolution of and with : while slowly decreases, increases sharply
increase of .
Hysteresis loops measured in the antidots region with the
field applied at different angles with respect to the e.a.
The inset shows the transverse susceptibility dependence on the
saturating field value .
Measured in the EUITT UPM by F. Pigazo and F. Cebollada.
Experimental angular dependence of the switching fields of the array,
to . Measured
in the EUITT UPM by F. Pigazo and F. Cebollada.