iaa NANOSTRUCTURED FERROMAGNETISM
the surface and the film is examined by an optical microscope, it is found that some
o f the magnetic particles i n the fluid agglomerate to form needle like chains parallel
to the direction of the magnetic field. Figure 7.23 depicts the chains viewed through
an optical microscope. As the magnetic field increases more particles join the chains,
and the chains become broader and longer. The separation between the chains also
decreases. Figures 7.24a and 7.24b show plots o f the chain separation and the chain
width as a function of the DC magnetic field. When the field is applied perpendicular
to the face ofthe film the ends of the chains arrange tlicmsclves i n the pattern shown
s 25:
z
g 0 2 0 i
z
z 15:
g
$ 10:
-2
: 5 f
0
-
-
-
. . .
-
.
-
1
1
'
1
'
~
~
~
"
"
'
'
'
"
'
~
~
s 25:
z
g 0 2 0 i
z
z 15:
g $ 10:
-2
: 5 f
.
_LLLL
20
0
I
L
.
5 ~ , , , 1 , , , 1 , , , 1 , " 1 " ' 1 , , ,
4.5 :
0
-
g 4 5
0
-
-
3.5 i
0
0
0
E
k
r 3 :
D
-
5 2.5
2
-
LL
40
.
Y
.
LL
60
.
-
80
100
Figure 7.24. (a) Plot of separation of magnetic nanoparticle chains versus strength of a
magnetic field applied parallel lo the surface of the film; (b) plol of the width of the chains as
a lunction 01 DC magnetic field strength. An oersted corresponds to lO-'T. [Adapted Irom H. E.
Hornig el al.. J. Phys. Chem. Solids 62, 1749 (2001).]