Biomedical Engineering Reference
In-Depth Information
2.0
2.0
BFO-40_MH_300K
BFO-50_MH_300K
1.5
1.5
1.0
1.0
0.5
0.5
0.0
0.
0
-150000 -100000
-50
000
0
50000
100000
150000
-150000 -100000
-50
00
0
0
50000
100000
150000
Magnetic Field(O e)
Magnetic Field (Oe)
-0.5
-
0.5
-1.0
-1.0
-1.5
-1.5
-2.0
-2.0
(
a
)
(
b
)
Figure 13.26
M~H curve of Bi
1-x
La
x
FeO
3
(x=0.4 and X=0.5) measured at RT.
with increased area without saturation. h e observed values of remnant
magnetization were 2.432 emu/g and 2.735 emu/g in the case of x=0.4 and
0.5 respectively.
Further, there is increment in coercive i eld with the increase of La
content, which is nearly zero for undoped BiFeO
3
. h e appearance of
ferromagnetism in the La-doped BiFeO
3
ceramics may arise due to the
destruction of spin cycloid structure which resulted in limited increase of
magnetization. Structural transformation (due to La-ion) destroys the spin
cycloid and releases the latent magnetization locked within the cycloid,
resulting in enhancement of magnetic properties. Here the question arises
whether M
r
and H
c
in x=0.1-0.5 truly arises from the collapse of the space
modulated spin structure or is caused by other factors such as presence
of Fe
2
O
3
and/or impurity phases and the change from canted antiferro-
magnetic order to ferromagnetic order. h e clarii cation is based on the
article by Yuan
et al.
[114]. h e x=0.1-0.2 samples have larger H
c
(≈ 9 kOe)
compared to Fe
2
O
3
impurity (< 100 Oe). h us it is quite unlikely that this
small M
r
is a result of small Fe
2
O
3
impurity present in the material. h e
Curie point of other impurity phases, if present, is much lower than the
room temperature, which indicates the null ef ect of impurity on M
r
. h e
samples exhibit small magnetization compared to nominal ferromagnetic
compounds and could be termed as weakly ferromagnetic. Hence the mag-
netization observed in x=0.1-0.5 is due to the collapse of spiral spin struc-
ture. h e observed values of remanent magnetization and coercive i eld are
tabulated in Table 13.6.
h e remanence versus x (concentration) curve is shown in Figure 13.27.
h e curve shows that the values of M
r
increases with the increase of La-ion
concentration.
