MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

86 Chapter 4
Resistivity (10 -3 Ω cm)
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5
4
3
2
1
Resistivity (10 -3 Ω cm)
5
4
3
2
La 0.67 Sr 0.33 MnO 3 Magnetoresistance
La 0.67 Sr 0.33 MnO 3 Film
R (H=0)
∆R/R
M
340 345 350 355 360 365 370 375 380
Temperature(K)
Pellet 0kOe
Pellet 70kOe
Film 0kOe
Film 70kOe
0
0 50 100 150 200 250 300 350 400
Temperature (K)
Figure 4-6 Magnetoresistance of La 0.67 Sr 0.33 MnO 3
polycrystalline pellet and Film (LSM1). Inset, simultaneous
magnetization and resistivity of the film at 20Oersted, along
with the magnetoresistance [R(H = 0 kOe)-R(H = 70 kOe)].
4. 2. 1 Low Temperature Resistivity
Low temperature resistivity data were analyzed using a polynomial
expansion in temperature T. Since the resistivity is essentially constant for
temperatures less than 10K for all samples, it is clear that the resistivity data
both with and without an applied field require a temperature independent
(R 0 ) term. As shown previously for related compounds [29, 104, 108], R 0 is a
function of magnetization in polycrystalline La 0.67 AE 0.33 MnO 3 (Figure 4-8) as
discussed in section 4.2.8. In contrast, the magnetoresistance of films and
crystals at 5 K is over 100 times less: it is not even measurable in the
La 0.67 Ca 0.33 MnO 3 crystal where the precision is 0.5%. Due to the higher
resistance of the films, the magnetoresistance at 5 K is measurable and is
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26
24
22
Magnetoresistance (%)