MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

76 Chapter 3
ferromagnet. Instead, it peaks as shown in Figure 3-19 near the compensation
temperature T Comp .
Susceptibility (µ B /T)
0.5
0.4
0.3
0.2
0.1
Calculated Susceptibility of Gd 0.67 Ca 0.33 MnO 3
χ = (M(6T) - M(4T))/2T
0
0 20 40 60 80 100
Temperature (K)
Figure 3-19 High field differential susceptibility for
Gd 0.67 Ca 0.33 MnO 3 calculated using the mean field model. The
maximum is at 11.5 K which is near T Comp = 14.2 K in this
model.
3.3 Heat Capacity
The heat capacity of a sample, particularly at low temperatures, is a
powerful experimental technique which gives fundamental information
about low-lying excitations of many kinds (phonons, electrons, magnons,
etc.). Microscopic models which describe these excitations typically give
quantitative predictions of the specific heat which can then be used to check
the theory. The has been quite successful at low temperatures where the
excitations are simple. At higher temperatures, the dispersion relation of the
excitation spectrum can become less simple and therefore complicate the heat