MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

142 Chapter 7
(Figure 7-6), in so far as the H dependence is concerned; however, the
exponential dependence upon M is found, as will be shown below.
ρ ∞ (mΩcm)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
ρ ∞
σ 0 and ρ ∞ above T C
280 290 300 310 320 330
Temperature (K)
Figure 7-8. Fitting parameters σ 0 and ρ ∞ for T > T C in a
La 0.67 Ca 0.33 MnO 3 film. The temperature dependence of these
two parameters reflect the insulating behavior of the material.
7. 2. 1 Magnetoresistance scaling above T C
The magnetoresistance data at various temperatures above T C were fit to
the expression ρ = ρ ∞ + 1/(σ 0 + σ H 2H 2 ). The resulting parameters σ 0 and ρ ∞ are
shown in Figure 7-8. The parameter σ 0 remains relatively constant, slightly
increasing as expected for a semiconductor. The significance of ρ ∞ will be
discussed below.
σ 0
0.20
0.15
0.10
0.05
0.00
σ 0 (mΩcm -1 )