Temperature and field dependence of the phase separation, structure, and magnetic ordering inLa1−xCax

Abstract

2 phase diagram obtained from the diffraction measurements is in good agreement with the results of magnetization and resistivity. Overall the measurements underscore the delicate energetic balance between the magnetic, structural and electronic properties of the system.

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

“…5 (c,d)). This could be due to the variation of relevant bond distances, documented in the neutron diffraction studies [5,7] and/or the effect of magnetic order on corresponding force constants, similar to those reported for other magnetic materials [21,22].…”

“…These new lines in the spectra could be a consequence of either the formation of a novel orthorhombic phase below T C =234 K, which has the same symmetry (space group Pnma), but slightly different lattice parameters compared to the room temperature phase of La 1/2 Ca 1/2 MnO 3 [7], or the appearance of a superstructure with doubled a lattice parameter and the space group P2 1 /m [5]. The observed intensity increase over rather wide temperature interval below T C indicates that the volume fraction of the novel phase increases upon sample cooling, in agreement with [7]. Note that appearance of vibrational modes with very similar frequencies was reported in charge ordered (LaPrCa)MnO 3 [17].…”

“…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. Of particular interest is the phenomenon of charge and orbital ordering, most clearly pronounced for x=1/2 [4,5,6,7,8,9,10].…”

“…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. Of particular interest is the phenomenon of charge and orbital ordering, most clearly pronounced for x=1/2 [4,5,6,7,8,9,10].In this communication we report the results of an infrared reflection study of La 1/2 Ca 1/2 MnO 3 over broad frequency range and at temperatures, covering the transitions from the high temperature paramagnetic to ferromagnetic and, upon further cooling, to antiferromagnetic phase. By making use of Kramers-Kronig analysis we obtained the spectral dependence of conductivity.…”

“…5 (c,d)). This could be due to the variation of relevant bond distances, documented in the neutron diffraction studies [5,7] and/or the effect of magnetic order on corresponding force constants, similar to those reported for other magnetic materials [21,22].It is important to note that the dielectric response of La 1/2 Ca 1/2 MnO 3 , as obtained from the reflection spectroscopy data, is consistent with the phase separation sce-3 nario for manganese oxides (see review [23] and references cites therein). Indeed, even below T N the dielectric function is not typical of an insulator, but contains the Drudelike component, a signature for presence in the sample of a conducting phase.…”