Electron, spin-wave, hyperfine, and phonon contributions to the low-temperature specific heat of La0.65Ca0.35MnO3: Effects of magnetic fields and O-16/O-18 exchange - art. no. 134425
Ra. Fisher et al., Electron, spin-wave, hyperfine, and phonon contributions to the low-temperature specific heat of La0.65Ca0.35MnO3: Effects of magnetic fields and O-16/O-18 exchange - art. no. 134425, PHYS REV B, 6413(13), 2001, pp. 4425
The field-dependent low-temperature specific heat of an optimally doped pol
ycrystalline sample of La0.65Ca0.35MnO3 (T-C=265 K), 1 less than or equal t
oT less than or equal to 32 K and 0 less than or equal toH less than or equ
al to9 T was analyzed by a global least-square fit to separate the hyperfin
e, electronic, spin-wave, and lattice contributions. The hyperfine and spin
-wave contributions are in quantitative agreement with nuclear magnetic res
onance and inelastic neutron-scattering results, respectively, This agreeme
nt supports the validity of both the data and their analysis. The calculate
d 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. T
he 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 neede
d for O-18 homogeneity produced modifications to both the long-wavelength p
honons 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 c
omposition.