Theoretical study of anisotropy in orbital and antiferromagnetic spin orderings in CMR manganites

摘要

We report here a tight binding model for doped rare earth manganites consisting of Kubo-Ohata type double exchange (DE) interaction between the eg and t2g band electron spins of same site. A Heisenberg type antiferromagnetic spin-spin interaction is considered among the core band electrons. Both nearest and next nearest neighbouring interactions are taken in the Heisenberg coupling and kinetic energy interaction. The presence of DE interaction induces antiferromagnetism (AFM) in eg band. The Jahn-Teller (JT) distortion leads to anisotropy in the manganite systems. We have considered JT distortion as an extra mechanism. The model Hamiltonian is solved using Zubarev's Green's function technique. The interplay between temperature dependent lattice strain and transverse spin fluctuations is studied. We have studied the in-plane anisotropy observed in the AFM spin fluctuation and its effect on the lattice strain.