Low temperature specific heat analysis of LaMnO3+delta manganites

摘要

We report a theoretical analysis for the experimental specific heat C(T) data of the perovskite manganites LaMnO3+delta, with delta = 0.11, 0.15 and 0.26, in the temperature domain 4 <= T <= 10 K. Calculations of C(T) have been made within the two-component scheme: one is the Fermionic and the other is Bosonic (phonon or magnon) contribution. Lattice specific heat is well estimated from the Debye temperature for lanthanum manganites with different 6 obtained following an overlap repulsive potential. Fermionic component as the electronic specific heat coefficient is deduced using the band structure calculations. Later on, following double exchange mechanism the role of magnons is assessed toward specific heat and is found that at low temperatures, specific heat shows almost T-3/2 dependence on the temperature. We note that the lattice specific heat is smaller for delta = 0.11 when compared with that of magnon specific heat below 6 K, while the lattice contribution is larger with the magnon contribution for 6 = 0.15 and 0.26. It is further noticed that in the ferromagnetic phase, deduced electronic specific heat is smaller in comparison with reported large electronic term in low temperature domain. The present investigations allow us to stress that electron correlations are essential to enhanced density of state over simple Fermi liquid approximation in pure LaMnO3+delta (6 = 0.11, 0.15 and 0.26). These findings express that the large Coulomb interaction U suppresses the double occupancies of eg electrons and enhanced electronic specific heat, while there is a decrease of T-3/2-term with delta from 0.26 to 0.11. The present numerical analysis of specific heat shows similar results as those revealed from experiments.