MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

Magnetoconductivity in La 0.67 Ca 0.33 MnO 3
kOe emu) -1 is estimated. For equal longitudinal and transverse
magnetoresistance, γ 2 + γ 3 ≈ 0.
The |H| form of the magnetoresistance below T C provides a cusp in the
magnetoresistance near H = 0. This is in contrast to the rounded curve
observed above T C .
6.2.1.1.3 Anisotropic magnetoresistance
The low field data are shown in Figure 6-2 with the average of the
transverse and longitudinal magnetoresistances. The vertical offset of these
data is approximate, i.e. it is calculated from measurements of a different,
patterned sample. The switching of the resistivity at +/-65 Oe is due to the
switching of the magnetization (coercivity). This can be seen in Figure 6-2
where the magnetization, relative to the saturated 0.9 T C value of about
1µ B /Mn, is shown for comparison.
The anisotropic magnetoresistance (AMR) at 0.9T C appears to provide the
nonlinear magnetoresistance in low fields, (Figure 6-2) aside from the
magnetization switching at 65 Oe. Since 1/(ρ trans + ρ long ) ≈ α 2 (E trans •M) 2 +
α 2 (E long •M) 2 ≈ α 2 M 2 (Cos 2 (θ) + Cos 2 (θ + 90°)) = α 2 M 2 , the sum of the transverse
and longitudinal resistances should be independent of the direction of M,
leaving only the magnetoresistance linear in H (Figure 6-2). This is
approximately what happens. The larger (smaller) than linear peak
(depression) in the longitudinal (transverse) magnetoresistance for H < 100
Oe is apparently due to AMR since the sum produces a curve which looks
like |H| that switches at the coercive field. Similar AMR has been
independently verified elsewhere [159].
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