Dynamic distortions and polaronic effects in the paramagnetic state of La0.8Ba0.2Mn1−xAlxO3 manganites

Abstract

Dynamic distortions and polaronic effects have been investigated in La0.8Ba0.2Mn1–xAlxO3 doped manganites of R3¯c symmetry. We studied the transport and magnetic properties and constructed a phase diagram of this system. We also analyzed the dependence of the transport data on the doping level x. The dependence of the polaron activation energy in the paramagnetic state on x doping was calculated and compared with the available literature data. The results suggest an interplay between a magnetic polaron mediated conductivity which dominates at low x and a bipolaron mediated one which controls electric transport at higher doping. It is suggested that the magnetic polaron formation is responsible for the increased magnetoresistance at low Al doping. Investigation on the nature of the magneto-transport mechanism of such ferromagnetic manganite will be useful in understanding its potential applications at the paramagnetic state.

Influence of Al-doping on the structural, magnetic, and electrical properties of La0.8Ba0.2Mn1−Al O3 (0 ⩽ x ⩽ 0.25) manganites

“…Can be seen a slightly shift to right hand side in all peak with increasing Al ion substitution. is 0.645Å) 15,20 . By comparing the samples annealed at higher temperatures, it can be observed that all of lattice parameters increases with increasing annealing temperature.…”

“…One of these compounds is La 1−x Ba x MnO 3 (LBMO) manganite. [15][16][17][18][19] . As trivalent La 3+ ions are replaced with a divalent Ba 2+ in LaM nO 3 manganite, some of the manganese ion valence changed from M n 3+ (with the electronic configuration 3d 4 , t 3 2g e 1 g , S=2) to M n 4+ (with the electronic configuration 3d 4 , t 3 2g e 0 g , S=3/2) due to introducing holes into the this material.…”

“…Based on the foregoing, the La 1−x Ba x Mn 1−x Al x O 3 manganite is one of the most attractive manganites. The La 1−x Ba x Mn 1−x Al x O 3 manganite having the T C and T N (Neel temperature) in the temperature range of 295 − 50 K for doping range of 0 ≤ x ≤ 0.8 15 .…”

Spin-dependent and spin-independent channels of electrical transport in perovskite manganites

“…18 The comparable results indicate that the TCET model in this work is similar to the CCDC model. 13,14,[18][19][20] However, the physical mechanism of the TCEP model, which includes spin-dependent and spin-independent electron transitions, is easier to be understood than that of the CCDC model, which assumes that the current-carrier density changes sharply at the magnetictransition temperature. Tables 2 and 3 show that among the ferromagnetic samples, E 3 of polycrystalline La 0.6 Sr 0.4 MnO 3 (65.0 meV) is far higher than that of single-crystalline La 0.6 Sr 0.4 MnO 3 (0.05 meV) owing to scattering at the crystallite interfaces in the polycrystalline sample.…”

“…17 Alexandrov et al 13,14 therefore established a current-carrier-density collapse (CCDC) model for the electrical-transport mechanism, and many researchers followed with investigations on this CCDC model. [18][19][20][21] The presence of p holes of oxygen anions in an oxide can be easily understood as there are O 1À anions in addition to O 2À anions. When compared with an O 2À anion (2s 2 2p 6 ) with a closed outer electron shell, it is clear that a p hole exists in the outer orbit of an O 1À anion (2s 2 2p 5 ).…”