Short-range ordered phase of the double-exchange model in infinite dimensions

Abstract

Using dynamical mean-field theory, we have evaluated the magnetic instabilities and T = 0 phase diagram of the double-exchange model on a Bethe lattice in infinite dimensions. In addition to ferromagnetic (FM) and antiferromagnetic (AF) phases, we also study a class of disordered phases with magnetic short-range order (SRO). In the weak-coupling limit, a SRO phase has a higher transition temperature than the AF phase for all fillings p below 1 and can even have a higher transition temperature than the FM phase. At T = 0 and for small Hund's coupling J H , a SRO state has lower energy than either the FM or AF phases for 0.26 ≤ p < 1. Phase separation is absent in the J H → 0 limit but appears for any non-zero value of J H .

Magnetic Susceptibility and Order Parameter of the Spin-Glass-Like Phase of the Double-Exchange Model

“…In a typical spin glass, such as CuMn [8], the RKKY interactions between randomly alloyed Mn ions produce a disordered ground state with a massive degeneracy. Recent work [9] on the DE model has revealed that the competing RKKY interactions between magnetic moments on a Bethe lattice can stabilize a phase with short-range but not longrange magnetic order [10]. We now show that the magnetic susceptibility of this SGL phase has a cusp at T SGL , marking the onset of short-range order, and reaches a nonzero value as T !…”

“…But as shown in Ref. [9] using dynamical mean-field theory (DMFT), the competing FM and AF interactions may actually favor a SGL phase over the ordered phases for small J H .…”

“…Since the Bethe lattice is not translationally invariant, q 0 is the only well-defined wave vector [9].…”

“…Detailed discussions of the T 0 phase diagram and magnetic instabilities of the DE model, including the issue of phase separation, are contained in Ref. [9].…”

Intrinsic inhomogeneities of low-doped lanthanum manganites in the paramagnetic temperature range

“…Such polarons apparently affect the magnetic and electric properties at high temperatures. Calculations in the double exchange model [41] show the existence of a short range ordered magnetic phase at T = 0 and its conservation at T > T C . The transition to a low sym metry orthorhombic phase with Jahn-Teller distor tions can be assumed to contribute to the localization of carriers.…”