Momin Hossain Khan

Magnetization reversal and ferrimagnetism in Pr 1− x Nd x MnO 3

Detailed magnetic properties of Pr1−xNdxMnO3 (x = 0.3, 0.5 and 0.7) have been reported. All the samples crystallize in orthorhombic perovskite structure with Pnma space group. Magnetization measurements under field cooled (FC) protocal reveal magnetization reversal at low temperatures and low magnetic field. This indicates clear evidence of two magnetic sublattices aligned opposite to each other. There is a well-defined maximum around 48 K in the x = 0.7 sample (i.e. Pr0.3Nd0.7MnO3) in the χ′ value which is identified as paramagnetic to ferrimagnetic transition. The peak value shifts to higher temperature with decrease of x and width of the maximum broadened. It is also observable that with decrease of Nd, both the value of χ′ and χ″ decrease. An attempt is made to explain the magnetization reversal within the framework of available models.

Metal-insulator transition and non-adiabatic small polaron hopping conduction in electron-doped Ca0.85Pr0.15MnO3 manganite

We report the detailed analysis of magnetic-field-dependent electrical transport properties of Ca0.85Pr0.15MnO3 (CPMO) over a wide temperature range (5–300 K) in absence and presence of applied magnetic fields as high as 15 T. The resistivity undergoes a metal-insulator (M-I) transition. We report the effect of magnetic field on the transition temperature that decreases with the applied field. The M-I transition in this compound may be due to the spin-state transition from a high spin state to a low spin state of Mn3+ ions. Temperature-dependent resistivity fitting above TMI (M-I transition temperature) suggests that electrical-conductivity carriers are mainly scattered by the electron–phonon interaction. In the semiconducting region, the conduction mechanism follows nonadiabatic, small-polaron hopping (SPH) above θD/2 (θD is the Debye temperature) and Mott-type variable range hopping (VRH) below θD/2. It has also been found that the density of states (DOS) at the Fermi level increases, whereas the hopping energy Whop decreases with external magnetic field.

Nonlinear behavior and universal scaling of ac conductivity in (100???x) BaTiO3/(x) La0.7A0.3MnO3 (A?=?Pb/Ca) composites

We have measured the ac conductance ? (x,f) of the ferroelectric?ferromagnetic (100???x) BaTiO3/(x) La0.7A0.3MnO3 (A?=?Pb/Ca) composites as a function of frequency (f) by varying x in wt% (20, 30, 40 and 50%) at a constant temperature T (300?K). ? (x,f) of the sample with fixed x remains at an almost constant dc value ? 0 at a lower frequency at a fixed temperature T. With the increase of f, ? (x,f) increases slowly from ? 0. Finally, ? (x,f) increases rapidly with ffollowing a power law with an exponent n in the high frequency regime. In the scaled coordinate, the data for ?(x, f) fall on the same universal master curve, indicating the existence of a general scaling formalism for the ac conductivity in composite systems. The characteristic frequency fc scales with ? 0 as fc???? (0,x)xf , where xf is the onset exponent. We have also shown that fc, scaling formalism of ac conductivity data can be successfully applied in insulating/conducting composite systems irrespective of the conducting phase.

Effects of rare-earth doping on transport properties in isoelectronic perovskite manganites

In this work, we explore the temperature dependence transport properties of isoelectronic manganites Ca0.85Re0.15MnO3 (Re = La, Pr, Nd, Gd). Substitution of Re3+ for Ca2+ will bring Mn3+ ions and hopping between Mn3+ and Mn4+ facilitated by double exchange (DE) interactions is responsible for augmentation the electrical conductivity. Resistivity shows insulating behavior with an inflection near charge ordering temperature (TCO). ρ (T) follows Mott-type variable range hopping (VRH) for all the samples in the low-T region.

Study of Dielectric Relaxation at Room Temperature of the Composite (100-x) LCMO/(x) BTO

The frequency dependent complex impedance and dielectric behavior of (100-x) La0.7Ca0.3MnO3 (LCMO)/(x) BaTiO3 (BTO) has been investigated at room temperature (300K). Separate contributions from various factors such as bulk effect, grain boundary and interface effect have been established by fitting the cole-cole function of real and imaginary part of complex impedance. Dielectric data were well fitted in the frequency domain with modified Curie-Von Schweider (CS) functions. Both formalisms support a non-Debye relaxation process in the composites.