Ferromagnetic Kondo model for manganites: Phase diagram, charge segregation, and influence of quantum localized spins

The phase diagram of the ferromagnetic Kondo model for manganites was recently investigated using computational techniques by Yunoki et al. [Phys. Rev. Lett. 80, 845 (1998)]. In dimensions 1, 2, and infinity and using classical localized spins, this study suggested a rich low-temperature phase diagram with three dominant regions: (i) a ferromagnetic phase, (ii) phase separation between hole-undoped antiferromagnetic and hole-rich ferromagnetic domains, and (iii) a phase with incommensurate spin correlations. The purpose of the present paper is twofold: (a) First, a variety of computational results is here provided to substantiate and supplement the previous results by Yunoki et al., investigating a complementary region of couplings and densities; (b) second, studies using the Lanczos algorithm and the density matrix renormalization group method applied to chains with localized spin 1/2 (with and without Coulombic repulsion for the mobile electrons) and spin 3/2 degrees of freedom are discussed. The overall conclusion is that using fully quantum mechanical localized spins in one-dimensional systems, the phase diagram of the model is similar to the result obtained using classical t(2g) spins. This result provides support of the use of classical localized spins in more complicated problems, such as in dimensions larger than 1 and/or including phononic and orbital degrees of freedom, where the use of classical spins is crucial to simplify the complexity of the problem.