Environmental Engineering Reference
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Fig. 7.10.
MF calculation of the ordering temperature
T
N
in Pr, as
a function of the uniaxial pressure in the
a
-direction, compared with the
neutron-diffraction measurements of McEwen
et al.
(1983).
for the hexagonal ions. Neglecting the magnetoelastic coupling to the
cubic ions, we obtain from eqn (7.3.2) the following
γ
-strain contribution
to the magnetic Hamiltonian:
B
γ
2
O
2
(
J
i
)
2
+t
11
/
c
γ
+
O
2
(
J
i
)
γ
,
(7
.
4
.
3)
H
γ
(sta) =
−
B
γ
2
H
i
∈
hex
.
ions
in the presence of a uniaxial stress along the
ξ
-axis.
N
in (7.3.2) is
the total number of ions, or twice the number of hexagonal sites. At
zero temperature and zero magnetic field, the only effect of
H
γ
(sta),
within the effective (
J
= 1)-model, is that the crystal-field splitting
which determines the excitation spectrum becomes different for the two
polarizations, and for instance ∆
η
, giving the
J
η
-mode energies, is found
to be
∆
η
=∆
η
(
t
11
)=∆
−
B
γ
2
M
22
t
11
/c
γ
,
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