Electron, spin-wave, hyperfine, and phonon contributions to the low-temperature specific heat of La0.65Ca0.35MnO3:: Effects of magnetic fields and 16O/18O exchange -: art. no. 134425

The field-dependent low-temperature specific heat of an optimally doped polycrystalline sample of La0.65Ca0.35MnO3 (T-C=265 K), 1 less than or equal toT less than or equal to 32 K and 0 less than or equal toH less than or equal to9 T was analyzed by a global least-square fit to separate the hyperfine, electronic, spin-wave, and lattice contributions. The hyperfine and spin-wave contributions are in quantitative agreement with nuclear magnetic resonance and inelastic neutron-scattering results, respectively, This agreement supports the validity of both the data and their analysis. The calculated bandstructure electron density of states is enhanced by a factor of 1.25. Specific heat was measured for two pieces cut from the O-16 parent sample and processed in parallel to produce an O-18 and a reference O-16 sample. The parallel-processed samples have very much larger lattice contributions (similar to 50% at low temperatures) than the parent sample, and a somewhat larger electronic contribution. Evidently, the many processing cycles needed for O-18 homogeneity produced modifications to both the long-wavelength phonons and the electron density of states. The spin-wave contribution has a small shift-nearly within the experimental accuracy-expected for the O-18/O-16 exchange, while the hyperfine contribution is independent of isotope composition.