34.
The nature of the double-exchange (DE) interaction in lanthanum manganites is studied through chemical substitutions, Cs for
La, and high-pressure measurements. Static and high-frequency magnetic measurements and high-pressure electrical transport
studies were carried out on bulk polycrystalline and radio-frequency sputtered thin films of La
0.7-xCs
xCa
0.3MnO
3 for x=0-0.1. The samples are found to be cubic. Curie temperature T
c measurements provide evidence for bond-length-related weakening of DE as x is increased from 0 to 0.03. For higher x, the
bond-angle-related changes lead to an increase in the strength of DE. High-pressure mangetoresistance data indicate both bond
length and bond-angle-related increase of 10–20 K/GPa in T
c with pressure, with the largest increase measured for x=0.03. The rate of increase in the Curie temperature with pressure
decreases with increasing T
c. Anomalies are observed in the magnetic parameters for x=0.03. The Cs-concentration dependence of the low-temperature saturation
magnetization shows a minimum close to x=0.03. Ferromagnetic resonance studies at x-band reveal a 5% decrease in the g-value
for x=0.03 relative to the end members (x=0 and 0.1). The low-field magnetostriction for x=0.03 indicates a relatively strong
electron–phonon spin coupling compared to neighboring compositions.
Received: 15 May 2000 / Accepted: 24 July 2000 / Published online: 9 November 2000
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