Approach to the metal-insulator transition inLa1−xCaxMnO<

Abstract

We describe the evolution of the static and dynamic spin correlations of La1−xCaxMnO3, for x=0.1, 0.125 and 0.2, where the system evolves from the canted magnetic state towards the insulating ferromagnetic state, approaching the metallic transition (x=0.22). In the x=0.1 sample, the observation of two spin wave branches typical of two distinct types of magnetic coupling, and of a modulation in the elastic diffuse scattering characteristic of ferromagnetic inhomogeneities, confirms the static and dynamic inhomogeneous features previously observed at x<0.1. The anisotropic q-dependence of the intensity of the low-energy spin wave suggests a bidimensionnal character for the static inhomogeneities. At x=0.125, which corresponds to the occurence of a ferromagnetic and insulating state, the two spin wave branches reduce to a single one, but anisotropic. At this concentration, an anomaly appears at q0=(1.25,1.25,0), that could be related to an underlying periodicity, as arising from (1.5,1.5,0) superstructures. At x=0.2, the spin-wave branch is isotropic. In addition to the anomaly observed at q0, extra magnetic excitations are observed at larger q, forming an optical branch. The two dispersion curves suggest an anti-crossing behavior at some q0' value, which could be explained by a folding due to an underlying perodicity involving four cubic lattice spacings.

Effect of disorder in an orbitally ordered Jahn-Teller insulator

“…The magnetic order is of A-type with ferromagnetic planes coupled antiferromagnetically in the transverse direction. The orbital order is of Ctype, anti-correlated with the magnetic order [1], and is accompanied by long range ordering of the Jahn-Teller (JT) distortions of the MnO 6 octahedra. Upon hole doping, e.g.…”

Confined Spin Waves Reveal an Assembly of Nanosize Domains in FerromagneticLa1−xCaxHennion1, Moussa2, Lehouelleur3 et al. 2005Phys. Rev. Lett.Self Cite467210View full textAdd to dashboardCite

“…This sample has been first studied in zero field. Preliminary observations at 17K along [001]+[010]+[001] have been reported [5]. Results are described with decreasing temperature.…”

“…There, neutron diffuse scattering indicates the existence of magnetic inhomogeneities attributed to hole-rich clusters embedded in a hole-poor matrix [4], and a new spin-wave branch appears at smallq around F Bragg peaks. This new branch coexists with the spin-wave branch close to that of LaMnO 3 (SE type of coupling), attributed to the hole-poor matrix [5], which disappears at x=0.125 (F state). The ferromagnetic state which occurs in the range 0.125≤x<0.225 shows a quasi-metallic behavior below T C and an insulating one at lower temperature [6].…”

“…In Fig. 5 upper panel, the values J a,b and J c , determined at 150K from the q-independent levels are reported with the J values obtained at 10K from the spin wave branch of SE type observed in the low doping and undoped compounds [5]. Besides a small temperature effect (12% in the 10K-150K range), the variation of J a,b (x) and J c (x) is monotonous across the CAF/F boundary (J c =0 at x=0.125), showing a tendency to become isotropic at x=0.225 (metallic state).…”

Transition isolant-métal induite par dopage dans les manganites, sondée par les ondes de spin

“…On pourrait comparer ce résultat avec les deux branches d'ondes de spin observées dans les isolants binaires antiferromagnétiques Mn (1−x) Co x F 2 [11]. Dans ce cas, les 2 ions sont fixes dans le réseau.…”