Polaron relaxation and hopping conductivity in LaMn1−x_{1-x}Fex_{x}O3_3

Dc and ac transport properties as well as electric modulus spectra have been investigated for the samples LaMn$_{1-x}$Fe$_{x}$O$_3$ with compositions 0 $\leq x \leq$ 1.0. The bulk dc resistivity shows a temperature variation consistent with the variable range hopping mechanism at low temperature and Arrhenius mechanism at high temperatures. The ac conductivity has been found to follow a power law behavior at a limited temperature and frequency region where Anderson-localization plays a significant role in the transport mechanism for all the compositions. At low temperatures large dc resistivities and dielectric relaxation behavior for all the compositions are consistent with the polaronic nature of the charge carriers. Scaling of the modulus spectra shows that the charge transport dynamics is independent of temperature for a particular composition but depends strongly on different compositions possibly due to different charge carrier concentrations and structural properties.Comment: 9 figure

Exchange bias effect in alloys and compounds

The phenomenology of exchange bias effects observed in structurally single-phase alloys and compounds but composed of a variety of coexisting magnetic phases such as ferromagnetic, antiferromagnetic, ferrimagnetic, spin-glass, cluster-glass and disordered magnetic states are reviewed. The investigations on exchange bias effects are discussed in diverse types of alloys and compounds where qualitative and quantitative aspects of magnetism are focused based on macroscopic experimental tools such as magnetization and magnetoresistance measurements. Here, we focus on improvement of fundamental issues of the exchange bias effects rather than on their technological importance

Glassiness in charge dynamics of half-doped manganite: A study on oxygen-deficient charge-ordered R

We report signature of glassiness in charge dynamics for oxygen-deficient charge-ordered manganites, R0.5Ca0.5MnO3− δ, where R = Pr, Nd and Sm. Structural investigation reveals strong orthorhombic distortion in the oxygen-deficient specimens. Excellent agreement of the experimental data with the defect model, scaling of the complex dielectric plot as well as critical slowing-down behaviour of the freezing temperature suggest a charge-glass–like state at low temperature. The appearance of charge-glass state is proposed to be a consequence of frozen ionic and defect charges in the lattice triggered by oxygen deficiency in the charge-ordered compounds