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Fig. 4.12
Magnetocaloric and thermal properties (of Gd obtained by the mean
eld theory)
applied to the AMR model for different magnetic elds between 0 and 2.5 T.
a
Adiabatic
temperature change for magnetization and demagnetization.
b
Derivative of
the specic
magnetization over the temperature.
c
Specic heat
combination of the Weiss mean
c
magnetization and the magnetic contribution to the total specic heat, the Debye
model for the calculation of the lattice contribution to the total speci
eld model for the calculation of the speci
c heat and the
Sommerfeld model for the calculation of the electron contribution to the total
speci
c heat [
49
,
77
,
78
]. It should be noted that the demagnetization curve is
shifted for the corresponding value of the adiabatic temperature change at each
temperature in order to ensure the thermodynamic consistency of the model (see
Fig.
4.12
a). The inclusion of the magnetocaloric effect directly through the adia-
batic temperature change is associated with the assumption of a discrete,
'
on-off
'
magnetic
eld change during the (de)magnetization process. The models that apply
the magnetocaloric effect directly, but not through the governing equations, are
further limited by the Brayton-like AMR cycle, since other AMR cycles are based
on a time-dependent (de)magnetization with a simultaneous heat transfer.
Another approach to include the magnetocaloric effect into the AMR model is to
apply it directly in the governing equations through the
q
MCE
term. It is de
_
ned as
(the so-called built-in method):
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