N. Pavan Kumar

Specific heat and magnetization studies of RMnO3 (R=Sm, Eu, Gd, Tb and Dy) multiferroics

A series of multiferroic materials with the compositional formula RMnO3 (where R=Sm, Eu, Gd, Tb and Dy) were prepared by the well-known citrate gel technique. After characterizing the samples structurally, a systematic investigation of specific heat and magnetization studies were performed over the temperature range 4?300?K with different magnetic fields. Based on these studies, it was found that all the samples exhibit a transition in the temperature region 39?54?K and the transition is attributed to ordering of Mn3+ ions (TNMn3+). Further, the samples GdMnO3, TbMnO3 and DyMnO3 were found to exhibit another transition (Tlock) in the temperature range 20?29?K. Finally, yet another transition was exhibited by all the samples and it is attributed to the antiferromagnetic (AF) ordering of rare-earth ion moments (TNR3+). The entropy at the AF transition TNMn3+ was computed. Finally, using the specific heat data, the Debye temperature values were also calculated.

Thermopower Studies of Polycrystalline Ag Doped LaMnO3 Manganites

The effects of silver doping on the magnetotransport and thermopower of La1−xAgxMnO3 (0.05≤x≤0.30) have been investigated. For the sample with x=0.05, temperature dependent resistivity exhibits an insulating behavior, while thermopower is found to be large and negative over the measured temperature range. An increase in the Ag doping enhances the conductivity and shifts the metal-insulator transition temperature toward high temperature side. The low temperature thermopower data has been explained in terms of diffusion, magnon drag, and phonon drag effects and found that the magnon drag effect dominates in this region. Finally, the electrical transport in the high temperature region has been analyzed by using adiabatic small polaron hopping mechanism.

STRUCTURAL AND THERMODYNAMIC PROPERTIES OF MULTIFERROIC Y0.5Dy0.5MnO3

The structural and thermodynamic properties of polycrystalline samples of Y0.5Dy0.5MnO3 were investigated in order to investigate the effect of higher magnetic moment ion over Y ion. The structural transition from hexagonal to orthorhombic is observed at very high doping of Dy ion. Heat capacity measurements were performed at 2-300K in the application of different high magnetic field and the transition indicates the spin alignment of Mn3+(TNMn3+). By using heat capacity data also calculated Debye temperature of the series.