MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

Critical Transport and Magnetization of La 0.67 Ca 0.33 MnO 3
∆R/R (%)
0
-10
-20
-30
-40
-50
-60
-70
-80
ρ ∞
262 K ≈ T C La 0.33 Ca 0.67 MnO 3
n = 1.3
1/σ H H n
n
1/σ 0
-60 -40 -20 0
Field (kOe)
20 40 60
Figure 7-12. Magnetoresistance of La 0.67 Ca 0.33 MnO 3 film at 262
K ≈ T C . The solid line shows the fit (for the full data on a
linear scale) using the indicated equivalent circuit.
7. 2. 4 Relation to low temperature magnetoresistance
This qualitative correlation between the magnetization and the resistivity
may also account for the intrinsic, small, linear magnetoresistance (Figure 4-
8) found even at the lowest temperatures where the magnetization is nearly
saturated. If at these low temperatures σ = σ 0 + σ M 2M 2 then ∆σ/σ (or ∆ρ/ρ) is
given by ∆σ = 2χσ M 2M 0 H. Since ∆σ = -∆ρ/ρ 2 , the susceptibility χ required to
give the observed magnetoresistance is χ = -∆ρ/(2ρ 2 σ M 2M 0 H ) = 2.5 × 10 -4
emu/Oe cm 3 using the results from chapter 4 for ∆ρ/H = -1.5 × 10 -8 mΩcm/Oe,
ρ = 0.125 mΩcm, and M 0 = 3.4 µ B /Mn = 550 emu/cm 3 . This is within a factor
of three of the observed value (section 4.2.9, Figure 4-8) χ = 9 × 10 -5
emu/Oe cm 3 . Similarly acceptable, is the exponential model
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