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首页> 外文期刊>Physical review, B. Condensed matter and materials physics >Spin waves in the ferromagnetic metallic manganites La_(1-x)(Ca_(1-y)Sr_y)_xMnO_3
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Spin waves in the ferromagnetic metallic manganites La_(1-x)(Ca_(1-y)Sr_y)_xMnO_3

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摘要

We have measured the spin-wave dispersion in the ferromagnetic metallic phase of five manganite compounds: La_(0.7)(Ca_(1-y)Sr_y)_(0.3)MnO_3 with y = 0, 0.2, 0.4, and 1 and La_(0.8)Sr_(0.2)MnO_3. An apparent broadening of the spin waves at the zone boundary in the 001 direction was observed, in agreement with previous work. Detailed investigation of this broadening by carefully separating lattice and magnetic contributions to the scattering cross section revealed that this observation is an artifact of the proximity of an optical phonon branch and the magnon branch. Upon separating out the magnon contribution, it becomes clear that the two branches are not strongly coupled and neither mix with nor damp each other within experimental uncertainty. Thus our experiment rules out significant magnon-phonon coupling. We also found that the softening of the spin-wave energy near the zone boundary appears in the manganites with low (y = 0) and high (y = 1) Curie temperatures regardless of their crystal structure. Thus it is not related to the existence of correlated polarons. Finally, we report the evolution of the magnetic couplings with doping throughout the whole phase diagram. To explain the observed continuity of the exchange component of the magnetic coupling measured in the metallic phase, we consider a possible persistence of dynamical orbital fluctuations reminiscent of orbital ordering, which occurs in the low-doping insulating regime.

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