MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

Figure 5-7 Low temperature resistivity of Gd 0.67Ca 0.33MnO 3 crystal, ln(ρ) vs. 1/T 1/4 .
Inset a, comparison with ln(ρ/T ) vs. 1/T . Solid lines show linear best fit to the
data shown. Inset b, magnetoresistance of a film at 200 K and 300 K; solid line
is the quadratic fit. 112
Figure 5-8 Fourier transform of kχ(k) from (a) Mn K-edge and (b) Gd L III-edge data on
Gd 0.67Ca 0.33MnO 3 . The solid lines are data collected at T = 69 K, while the
triangles (Δ) are data collected at T = 40 K. Agreement between data above and
below T C is well within the errors of the experiment. Transform ranges for the
Gd edge data are from 3.5-12.5 Å -1 and Gaussian broadened by 0.3 Å -1 . Transform
ranges for the Mn edge data are from 3.2-12.5 Å -1 and Gaussian broadened by 0.3
Å -1 . 115
Figure 6-1 High field (longitudinal) magnetoresistance above and below T C for
La 0.67Ca 0.33MnO 3 film. The solid lines show the fit using the indicated equivalent
circuit 123
Figure 6-2 Low field magnetoresistance and magnetization (relative units) of
La 0.67Ca 0.33MnO 3 at 0.9 T C. The sum of the longitudinal and transverse resistances
minimizes the effect of the anisotropic magnetoresistance. 124
Figure 6-3 Hall effect of La 0.67Ca 0.33MnO 3 below (fully magnetized data only) and
above T C. 126
Figure 7-1. M 2 vs. H /M plot for La 0.67Ca 0.33MnO 3 float zone crystal. A mean field
ferromagnet has linear isotherms with a positive slope. The negative slope for T
>T C indicates a faster than linear increase in M (inset) due to a highly unusual
positive non-linear susceptibility χ 3. 130
Figure 7-2. Data from Figure 7-1 (using the same symbols) scaled with β = 0.27 and
γ = 0.90. According to the scaling hypothesis, all the T < T C data should lie on
a single curve while the T > T C data should lie on a separate, single curve. 131
Figure 7-3. Saturation Magnetization, M 0 as a function of temperature for
La 0.67Ca 0.33MnO 3 crystal. At each temperature, the value shown is M extrapolated
to H = 0 as given by the intercept in Figure 7-1.Solid line is fit to M 0(T ) ∝ (1 -
T /T C) β with β = 0.30. 1 3 3
Figure 7-4. Inverse magnetic susceptibility, 1/χ 0 as a function of temperature for
La 0.67Ca 0.33MnO 3 crystal. At each temperature, the value shown is H/M
extrapolated to H = 0 as given by the intercept in Figure 7-1. Solid line is fit to
1/χ 0 ∝ (T /T C - 1) γ with γ = 0.7 and T C = 263K. 136
Figure 7-5. Magnetization in a magnetic field for a La 0.67Ca 0.33MnO 3 polycrystalline
pellet at 0.9 and 1.1 T C. The solid lines indicate the linear regions in each case.139
Figure 7-6. Magnetoresistance of La 0.67Ca 0.33MnO 3 film compared with -M 2 of a pellet,
both at 0.9 T C. The solid line for the magnetoresistance data shows the fit using
the indicated equivalent circuit. The dashed line in the inset compares the
exponential fit. 140
Figure 7-7. Magnetoresistance of La 0.67Ca 0.33MnO 3 film compared with -M 2 of a pellet,
both at 1.1 T C. The solid line for the magnetoresistance data shows the fit using
the indicated equivalent circuit. 141
Figure 7-8. Fitting parameters σ 0 and ρ ∞ for T > T C in a La 0.67Ca 0.33MnO 3 film. The
temperature dependence of these two parameters reflect the insulating behavior of
the material. 142
Figure 7-9. Fitting parameter σ H2 as a function of temperature in a La 0.67Ca 0.33MnO 3
film for T > T C. The temperature dependence of σ H2 and the square of the
susceptibility are the same, indicating a relationship between the
magnetoconductance and M 2 . 143
Figure 7-10. Fitting parameters σ 0 and ρ ∞ for T < T C in a La 0.67Ca 0.33MnO 3 film. ρ ∞ is
governed by the A + BT 2 terms in the resistivity while σ 0 diverges at T C. The
inset shows σ 0 data fit with a (T C - T) 1.8 power law (dashed line), and σ ∝
exp(M /M E) (solid line). The zero field resistivity ρ(H = 0) = ρ ∞ + 1/σ 0 is shown
for comparison. 145
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