MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

170 Appendix A
excitations for T < gµ B H/k B , resulting in an effective n > 3/2. If this were a
significant effect, the T 3/2 fitting parameter A should decrease as H is increased
particularly as T max approaches 0 K. Such a systematic decrease in A is not
obviously apparent (Figure A- 8). One cannot however, exclude the
demagnetization or anisotropy field which are present even when the applied
H = 0.
AT 3/2 Coefficient (10 -6 /K 3/2 )
140
120
100
80
60
40
20
M = 1 - (T/400 K) 3/2 - (T/600 K) 5/2
fit with M = M (1 - AT
S 3/2 - BT2 )
A
B
0
0.0
0 20 40 60 80 100
Maximum Temperature (K) of Fitting Range
Figure A- 11. Variation of A and B fitting parameters in the
hypothetical case where the true magnetization is given by T 3/2
and T 5/2 terms.
If the true magnetization were a sum of T 3/2 and T 5/2 terms, M/M S =
(1 - (T/400 K) 3/2 - (T/600 K) 5/2 ) for instance, the data would fit well to M/M S =
(1 - AT 3/2 - BT 2 ). The fitting parameters A and B as a function of T max for this
example are shown in Figure A- 11. The A parameter is relatively constant,
increasing slightly as T max approaches 0 K. In the limit T max approaches 0 K,
A = 125 × 10 -6 K -3/2 or Θ 3/2 = 400.3 K, which is very close to the true value of
400 K. The B fitting parameter is not nearly as stable and decreases as T max
2.0
1.5
1.0
0.5
BT 2 Coefficient (10 -6 /K 2 )