304
N. Kojima and A. Okazawa
Fig. 6.38 Molecular structure of [Fe 8 O 2 (OH) 12 (tacn) 6 ]Br 8 . The arrows represent the spin structure
triazacyclononane), respectively. These typical SMMs have been examined by means
of
57 Fe Mössbauer spectroscopy, which were well summarized in a preceding book
[64].
The [Fe 8 ] complex consists of eight Fe
III ions to form the ground S total = 10
state [65] and shows SMM behavior with frequency dependence of ac magnetic
susceptibilities giving τ 0 = 1.9 × 10
−7 s and /k B = 22.2 K [63]. The relaxation time
of magnetization was first investigated by means of
57 Fe Mössbauer spectroscopy
for a SMM. As shown in Fig. 6.39a, a clear magnetic sextet superimposed three
six-line patterns was observed in the
57 Fe Mössbauer spectrum at 2 K also under the
absence of an external field. On heating, the splitting collapses gradually and results
in partially-resolved quadrupole doublets at 300 K. A simplified line shape model
was applied to the Mössbauer spectra in order to compare the estimated relaxation
time with the values deduced from the ac magnetic measurements. The τ values
were reasonably evaluated as they are compatible with the Arrhenius law in the ln(τ )
versus T
−1 plot of ac measurements.
N. Kojima and A. Okazawa
Fig. 6.38 Molecular structure of [Fe 8 O 2 (OH) 12 (tacn) 6 ]Br 8 . The arrows represent the spin structure
triazacyclononane), respectively. These typical SMMs have been examined by means
of
57 Fe Mössbauer spectroscopy, which were well summarized in a preceding book
[64].
The [Fe 8 ] complex consists of eight Fe
III ions to form the ground S total = 10
state [65] and shows SMM behavior with frequency dependence of ac magnetic
susceptibilities giving τ 0 = 1.9 × 10
−7 s and /k B = 22.2 K [63]. The relaxation time
of magnetization was first investigated by means of
57 Fe Mössbauer spectroscopy
for a SMM. As shown in Fig. 6.39a, a clear magnetic sextet superimposed three
six-line patterns was observed in the
57 Fe Mössbauer spectrum at 2 K also under the
absence of an external field. On heating, the splitting collapses gradually and results
in partially-resolved quadrupole doublets at 300 K. A simplified line shape model
was applied to the Mössbauer spectra in order to compare the estimated relaxation
time with the values deduced from the ac magnetic measurements. The τ values
were reasonably evaluated as they are compatible with the Arrhenius law in the ln(τ )
versus T
−1 plot of ac measurements.