Effects of spin–phonon interaction on transport, magnetic properties and the oxygen isotope effect in R 1− xA xMnO 3

Abstract

We consider the spin–phonon ( s–p) coupling as an important correction to the double exchange and the dynamic Jahn–Teller effect in colossal magnetoresistance systems R 1− x A x MnO 3. The effect of s–p on transport, magnetic properties and the oxygen isotope effect has been studied by utilizing the perturbation theory and mean field theory. It is indicated that (i) a formula for the shift of the ferromagnetic (FM) transition temperature T c is given, from which it could be seen that the s–p coupling could yield an excitation gap for long-wavelength acoustic spin waves and an applied field could improve T c , (ii) the relation T c ∼ m −1/2 ( m is the mass of the anion) is obtained, which suggests that the oxygen isotope effect is dominated by both the s–p and e–p interaction, (iii) it could cause the hardening of phonon frequency in the FM state, (iv) s–p could lead to the increase of the resistivity which is proportional to T 3 at low temperature and proportional to T at high temperature in the ferromagnetic metallic region of R 1− x A x MnO 3.