MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

108 Chapter 5
of the nonlinear M 2 vs. H/M Arrott plot is given in Figure 5-4.
5. 1. 5 Magnetism model
To explain the magnetism, a mean field model was used assuming a
ferrimagnetic ground state. Other possible explanations for the magnetism in
Gd 0.67 Ca 0.33 MnO 3 are briefly discussed
5 kOe
Gd 0.67 Ca 0.33 MnO 3 Mean Field Calculation
Remnant
Gd
Mn
20 40 60 80 100 -5
Temperature (K)
3
2
1
0
-1
-2
-3
-4
Magnetization (µ B /mol)
5 kOe
0 50 100 150 200 250
0
300
Temperature (K)
Figure 5-5 Magnetization and inverse magnetic susceptibility
calculated for Gd 0.67 Ca 0.33 MnO 3 using the simplified mean field
theory described in the text and T C = 83 K, T Comp = 17 K. The
contribution to the magnetization of each sublattice is shown
in dashed lines.
5. 1. 5. 1 Mean Field Model
Due to the stronger 3d exchange interaction compared to that of the 4f, the
Mn-Mn coupling is expected to be stronger than the Mn-Gd, and the Gd-Gd
interaction to be negligible. Since the observed Curie temperature is about
40
35
30
25
20
15
10
5
1/χ (mol G/emu)