nological applications, a large number of synthesis methods have evolved in recent
years which include reverse micelle and sonochemical methods as well as laser
abalation. Control over size and shape as well as encasing the nanocrystals with
ligands of specialized functionalities have become subjects of urgent enquiry.
Semiconductor nanocrystals are becoming established as practical alternatives to
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
300 K
50 K
(b)
(a)
50 K
90 K
180 K
200 K
240 K
300 K
M (10
-3
emu)
H (T)
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
300 K
50 K
|
|
50 K
90 K
180 K
200 K
240 K
300 K
M (10
-3
emu)
H (T)
Fig. 4.31. Hysteresis loops from a film of
g-Fe 2 O 3 deposited on Si(100) substrates at
various temperatures with the substrate held
(a) perpendicular and (b) parallel to the
applied field direction. The increased coercivity
along the perpendicular direction indicates
perpendicular anisotropy caused by orientation
of the easy magnetic axis of g-Fe 2 O 3
nanocrystals perpendicular to the substrate.
4.5 Conclusions 87