Biomedical Engineering Reference
In-Depth Information
ferromagnetism. In fact, precise measurements performed using a time-of-
l ight neutron dif ractometer [105, 106] have revealed a quite complicated
magnetic structure. h e antiferromagnetic ordering possesses a spiral spin
modulation with a large period of λ = 620 ± 20 Å, which is also incommen-
surate with the fundamental lattice. Accordingly, the magnetic moments of
the iron ions retain their local mutually antiferromagnetic G-type orienta-
tion and rotate along the propagation direction of the modulation wave
in the plane perpendicular to the hexagonal basal plane. h e wave vector
of such a cycloid is perpendicular to the 3-fold axis and lies in the plane
of spin rotation. h e existence of the incommensurate cycloidal structure
has also been coni rmed by line-shape analysis of nuclear magnetic reso-
nance (NMR) spectra [107, 108]. h eoretical analysis has been performed
to explore the physics for the formation of such a structure. Because of the
cycloidal modulation, the net magnetization due to spin canting within
each pair of Fe
3+
ions and the volume-averaged magnetoelectric (ME)
ef ect are averaged to zero over a wavelength. [109] h is means that the
spontaneous magnetization of bulk single crystal BiFeO
3
should be zero
even though its symmetry permits weak ferromagnetism.
13.5.5 Experimental
h e DC magnetization M~H and M~T measurements were carried out at
room temperature (RT) and at low temperature (~10-325 K) under i eld
cooled (FC) and zero i eld cooled (ZFC) conditions using Vibrating sample
magnetometer (VSM) model PPMS-6000.
13.5.6
Some of the Important Results on Pure and Substituted
BiFeO
3
13.5.6.1
M~H at 300K (±14T)
h e magnetization curves (M~H) of all the samples were measured at
room temperature (300 K). Figure 13.24(a) shows the M~H response for
pure BiFeO
3
ceramics in which the sample exhibited straight line behavior
in the M~H curve up to the measured i eld of 14 T. It gives a clear cut indi-
cation of the antiferromagnetic nature consistent with our report [110] and
other literature reports [111-113].
Figure 13.24(b) shows the magnetization curve (M~H) for 10%
La-substituted bismuth ferrite Bi
1-x
La
x
FeO
3
(x=0.1) sample. It is evident
from Figure 13.24 that pure BiFeO
3
compound behaves like an antifer-
romagnet, whereas the 10% La-substituted compound shows very small
remanence (M
r
) of 0.588 emu/g.
