MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

124 Chapter 6
∆R/R (%)
1
0
-1
-2
-3
-4
Transverse
Sum
Longitudinal
-600 -400 -200 0 200 400 600 -1
Field (Oersted)
Magnetization
Figure 6-2 Low field magnetoresistance and magnetization
(relative units) of La 0.67 Ca 0.33 MnO 3 at 0.9 T C . The sum of the
longitudinal and transverse resistances minimizes the effect
of the anisotropic magnetoresistance.
6.2.1.1.2 T < T C regime
4
3
2
1
0
Relative
Magnetization
The longitudinal data fit well with three parameters (ρ ∞ = 0.58 mΩcm, σ ο =
0.35 (mΩcm) -1 and σ Η = 0.013 (mΩcm kOe) -1 ) to ρ(H) = ρ ∞ + 1/(σ ο + σ Η |H|). A
significantly less satisfactory fit is obtained with an exponential form [114,
156]: ρ(H) = ρ ∞ + ae -|H|/b .
Below T C and for M ≠ 0 parallel to H, i. e. M = MH/|H|, then up to terms
linear in H, σ(H) reduces to (σ 0 + α 1 M 2 ) + α 2 M 2 (E•H) 2 /E 2 H 2 + γ 1 M|H| +
(γ 2 + γ 3 )M|H|(E•H) 2 /E 2 H 2 . By fitting the 0.9T C data, γ 1 = σ Η /M = 73 × 10 -6 (mΩcm