Geoscience Reference
In-Depth Information
Figure 8.10 Variation of the inverse magnetic
susceptibility with temperature
[32]
.
Source: Courtesy of the Gauthier-Villars/ESME,
Paris.
2.5
2.0
1.5
1.0
0.5
0.0
0
100
200
300
θ
p
T
(K)
60 K).
The variation of the inverse magnetic susceptibility with the temperature is given in
Figure 8.10
for BaMn(CO
3
)F
2
.AboveT
Ferromagnetic interactions must also take place at low temperature (T
,
90 K, the linear Curie
Weiss law is well
obeyed, leading to a molar Curie constant C
M
5
4.39 (as compared to the theoretical
4.375 for Mn
2
1
) and a Curie paramagnetic temperature
value C
M
5
θ
p
52
52 K.
This value of
θ
p
, together with the deviation of 1/x from the Curie
Weiss law at
T
90 K indicates that antiferromagnetic interactions dominate; however, no clear
evidence of magnetic order can be found at a low temperature
[32]
.
Magnetic susceptibility of Mn
2
PO
4
F and CO
2
PO
4
F has been studied by Leblanc
et al.
[33]
. The variation of the inverse magnetic susceptibility Xg
2
1
with tempera-
ture (
Figure 8.11
) and the absence of field dependence of the susceptibility are
indicative of antiferromagnetic behavior with T
N
5
,
14 K for Mn
2
PO
4
F
and CO
2
PO
4
F, respectively. Above approximately 100 K, the Curie
15 and T
N
5
Weiss law is
well obeyed and yields
θ
p
52
50 K, C
M
5
8.2 and
θ
p
52
53 K, C
M
5
6.4. These
molar Curie constants, which give
μ
eff
5
5.70 and 5.1
μ
B
, are in good agreement
8.75 (spin only value) for Mn
2
1
and with the
with the calculated value C
M
(th)
5
value usually found for CO
2
1
.
8.7 Hydrothermal Synthesis of Tungstates
Tungstates form an important class of materials with a wide range of divalent and
trivalent metals in their composition. Among the trivalent metals, the rare earth and
