Biomedical Engineering Reference
In-Depth Information
2.1
Overview of the size dependence of coercivity exhibited by
magnetic particles.
higher for planes containing the highest population of nanoparticles in the
film, provided that the crystal film contains the same number of monolayers
but is grown in different directions. Thus, the highest T
c
is found along the
<
directions in the sc, bcc and fcc structures,
respectively. The common feature is that the most populated plane
corresponds to the most favorable growth direction and has the highest
T
c
value. Needless to say, the film tends to a bulk in any case as L
approaches infinity.
This chapter now moves on to review the properties of magnetic
nanoparticles such as coercivity, superparamagnetism and electrical trans-
port.
100
>
,
<
110
>
and
<
111
>
2.3
Size-dependent magnetic properties
Magnetic nanoparticles exhibit a number of magnetic properties that can be
attributed to the reduced dimensions of
the particles. These include
coercivity and superparamagnetism.
2.3.1 Coercivity
The coercivity [41-56] of magnetic nanoparticles has a striking dependence
on their size, as shown in Fig. 2.1. The coercivity H
c
is zero below the
superparamagnetic (SP) particle size limit r
0
, single-domain (SD) behavior
(SD) is shown between r
0
and the single-domain limit r
c
, and multi-domain
(MD) behavior for r
>
r
c
.
