426
M. Reissner
Fig. 8.45 Calculated (open
symbols ASW, full symbols
LAPW) hyperfine fields
B th
core (◦), B th
tot () and
B th
val () for Y(Fe x Al 1−x ) 2
[150]. © IOP Publishing.
Reproduced with permission.
All rights reserved
up to three nearest Fe neighbours C
M B
core values are constant. For higher iron concentration in the nearest neighbour shell an increase is present. From this it can be
concluded that Fe carries a moment even if surrounded only by Al atoms, in agreement with the band-structure calculations (Fig. 8.45). The increase of χ loc for the Fe
rich surroundings reflects the increase of the mean Curie constant ¯
C
M B
core and of μ e f f .
In summary, from magnetization and high field Mössbauer measurements and with
the help of band-structure calculations it could be proved that all iron atoms carry a
magnetic moment in the paramagnetic regime of the Y(Fe x Al 1−x ) 2 cluster glass.
Entering now the temperature regime T f < T <∼ 7 · T f , where magnetic correlations are present, visible in the bended magnetization curves, the Mössbauer
spectra in applied magnetic field change drastically their shape. Figure 8.47 shows
spectra for x = 0.75 at 1.8 · T f (left) and 5 · T f (right). The shape of the spectra at
13.5 T are quite different from those obtained at room temperature in the pure paramagnetic region (Fig. 8.43). The spectra can no longer be fitted by a superposition of
subspectra with intensities according to the different iron environments, calculated
by binomial distribution. The nearer the temperature to T f , the more is the deviation
in shape from the one for the paramagnetic case. Often spectra with similar shape
are analysed by distribution of static hyperfine fields [152, 153]. Figure 8.48 gives
M. Reissner
Fig. 8.45 Calculated (open
symbols ASW, full symbols
LAPW) hyperfine fields
B th
core (◦), B th
tot () and
B th
val () for Y(Fe x Al 1−x ) 2
[150]. © IOP Publishing.
Reproduced with permission.
All rights reserved
up to three nearest Fe neighbours C
M B
core values are constant. For higher iron concentration in the nearest neighbour shell an increase is present. From this it can be
concluded that Fe carries a moment even if surrounded only by Al atoms, in agreement with the band-structure calculations (Fig. 8.45). The increase of χ loc for the Fe
rich surroundings reflects the increase of the mean Curie constant ¯
C
M B
core and of μ e f f .
In summary, from magnetization and high field Mössbauer measurements and with
the help of band-structure calculations it could be proved that all iron atoms carry a
magnetic moment in the paramagnetic regime of the Y(Fe x Al 1−x ) 2 cluster glass.
Entering now the temperature regime T f < T <∼ 7 · T f , where magnetic correlations are present, visible in the bended magnetization curves, the Mössbauer
spectra in applied magnetic field change drastically their shape. Figure 8.47 shows
spectra for x = 0.75 at 1.8 · T f (left) and 5 · T f (right). The shape of the spectra at
13.5 T are quite different from those obtained at room temperature in the pure paramagnetic region (Fig. 8.43). The spectra can no longer be fitted by a superposition of
subspectra with intensities according to the different iron environments, calculated
by binomial distribution. The nearer the temperature to T f , the more is the deviation
in shape from the one for the paramagnetic case. Often spectra with similar shape
are analysed by distribution of static hyperfine fields [152, 153]. Figure 8.48 gives