Chemistry Reference
In-Depth Information
1
1
15 K
10 K
0
0
-1
-1
1
1
25 K
20 K
0
0
-1
-1
320
324
328
332
320
324
328
332
H
(MT)
H
(MT)
Fig. 7. The ESR signals in vacuum at 10, 15, 20, and 25 K measured with 16 mW (From
reference 26).
static susceptibility does not show any indications of non-Curie behavior
down to 2 K as shown in Fig. 6(c). These experimental findings are
therefore understood by the presence of a transition from the
homogeneous state to an inhomogeneous one at ca.20 K. This is clearly
evident in observing a change in the line profile in the vicinity of the
transition temperature (
T
c
~ 20 K). Figure 7 exhibits the ESR signal at a
strong microwave power of 16 mW in the vicinity of
T
c
.
26
The broadened
signal at 10 K shows a slight deviation from the Lorentzian shape
indicating an inhomogeneous line-broadening. Interestingly, a prominent
hole-burning effect (irregular feature in the ESR signal) appears at 15 K,
which is just below
T
c
, and it is reproducible in repeated runs. The hole-
burning feature is an important evidence of serious inhomogeneity
appearing in this temperature range. On going to higher temperatures,
hole-burning is gradually suppressed and the line-shape tends to become
Lorentzian. Above 25 K the line shape becomes sharpened and purely
Lorentzian, exchange/motional narrowing being indicated.
The experimental findings presented above allow us to understand
the magnetic structure and dynamics of the edge-state spin system. The
conductivity result suggests strong electron localization with the aid of
Coulomb interaction, particularly in the lower temperature region. In
