Phase diagram of theLa1−xCaxMnO

Abstract

We have studied the phase diagram of La 1Ϫx Ca x MnO 3 for 0.5рxр0.9 using neutron powder diffraction and magnetization measurements. At 300 K all samples are paramagnetic and single phase with crystallographic symmetry Pnma. As the temperature is reduced a structural transition is observed which is to a charge-ordered state only for certain x. On further cooling the material passes to an antiferromagnetic ground state with Néel temperature T N that depends on x. For 0.8рxр0.9 the structural transformation occurs at the same temperature as the magnetic transition. Overall, the neutron-diffraction patterns were explained by considering four phase boundaries for which La 1Ϫx Ca x MnO 3 forms a distinct phase: the charge-ordered phases at xϭ0.5 and x ϭ2/3, the monoclinic and C-type magnetic structure at xϭ0. 80-0.85, and the G-type magnetic structure at xϭ1. Between these phase boundaries the magnetic reflections suggest the existence of mixed compounds containing both phases of the adjacent phase boundaries.

Boson peak in overdoped manganites La1−xCaxMnO3

“…There is, however, some dispute about this Peierls-Fröhlich scenario [13,14]. In particular, the THz resonances can be self-consistently interpreted as acoustical lattice vibrations that acquire optical activity when the Brillouin zone is folded due to the superstructure in the CO state [15,16]. This superstructure and corresponding folded phonons are inherent fingerprints of the ordering in manganites.…”

Diffuse neutron scattering study of magnetic correlations in half-dopedLa0.5Ca0.5−xSrxDhiman1, Das2, Mittal3 et al. 2010Phys. Rev. B16380View full textAdd to dashboardCite

“…1,2 Neutron scattering studies in doping regime 0.15 ≤ x ≤ 0.30 have shown that the transport properties of these materials are controlled by the competition between short range charge correlations and long range ferromagnetic double exchange interactions. 3,4 Theoretical understanding enunciates that double exchange interaction alone is insufficient and strong electron -phonon coupling is also required.…”

Charge and lattice dynamics of ordered state in La1/2Ca1/2MnO3: infrared reflection spectroscopy study

“…[1,2,3] and references cited therein). Well defined anomalies of physical properties at commensurate carrier concentrations of x=N/8 (where N=1, 3, 4, 5, and 7) and x = L/3 (where L=1,2) were unambiguously established.…”

“…The material preparation technique is described in Ref. [3,9,11]. The samples were intensively characterized by the X-ray scattering, neutron diffraction, magnetization measurements, Raman scattering as well as Mössbauer spectroscopy (doped with 1% Sn or Fe).…”