I. Panneer Muthuselvam

Evidence of disorder induced magnetic spin glass phase in Sr2FeMoO6 double perovskite

The present work described the disorder induced magnetic properties of Sr2FeMoO6 (SFMO) samples. The crystal structure and magnetic order of SFMO samples with nanosized grains were studied using x-ray diffraction spectrum, scanning electron microscope morphology, and magnetic measurements. Thermal annealing of as prepared chemical routed materials showed an increase in grain size and in the magnetic moment per formula unit. A small decrease in magnetic moment was noted at higher annealing temperature. At the same time, the ac susceptibility measurement indicated the presence of a magnetic spin glass phase in the material, coexisting with the ferromagnetic matrix. The observation of the magnetic glassy phase confirmed the presence of intrinsic disorder in the lattice structure of SFMO. The signature of intrinsic disorder in the samples, irrespective of annealing temperatures, is also realized from the splitting of temperature dependent field cooled and zero field cooled magnetization curves. Such magnetic ...

Connectivity between electrical conduction and thermally activated grain size evolution in Ho-doped CoFe2O4 ferrite

Ho-doped CoFe2O4 spinel ferrite has been synthesized by a combination of mechanical alloying and subsequent annealing of the alloyed powder in the temperature range 950 °C ≤ TAN ≤ 1200 °C. The grains of the nanocrystalline samples have been found in the single domain/pseudo-single domain state for TAN ≤ 1050 °C and multi-domain state for TAN ≥ 1100 °C. The room temperature Fourier transform infrared spectroscopy spectrum of the samples indicated substantial changes in the tetrahedral sites of the cubic spinel structure while the alloyed powder was annealed at different temperatures. Ac conductivity of the nano-grained samples has been studied in the frequency range 1 Hz–3 MHz and temperature range 303–523 K. This work has been specifically designed to highlight the properties of electrical conductivity in the annealed samples. Experimental results revealed a strong connectivity between electrical conduction and the single domain and multi-domain states of the grains.

Disorder induced magnetism and electrical conduction in La doped Ca2FeMoO6 double perovskite

We report the magnetism and electrical transport properties of La doped Ca2FeMoO6 double perovskite. Reduction in magnetic moment, nonmonotonic variation in magnetic ordering temperature (TC), increasing magnetic hardness, low temperature resistivity upturn, and loss of metallic conductivity are some of the major changes that we observed due to La doping induced disorder in double perovskite structure. The increase in magnetic disorder in La doped samples and its effect on TC is more consistent with the mean field theory. The modification in electronic band structure due to La doping is understood by establishing a correlation between the temperature dependence of electrical conductivity and thermoelectric power.

Grain size dependent magneto‐transport in La0.67Sr0.33MnO3

We have investigated magneto‐transport properties of La0.67Sr0.33MnO3 perovskite with grain size micron to nanometer range. Grain boundary disorder is clearly indicated from the decrease of magnetic moment and magneto‐resistance of the samples. Magnetoresistance at different temperatures indicated that magnetic spin order at grain and grain boundary plays a significant role in controlling the magneto‐transport properties of the present system.

La Doped Disorder in LaxCa2−xFeMoO6 Ferrimagnet: Magnetic and Thermoelectric Study

We report the magnetic and thermo‐electric properties of LaxCa2−xFeMoO6 (xu2009=u20090 to 0.8) ferrimagnet. The ferromagnetic ordering temperature (TC) changes with increasing La doping. The band structure modification due to La doping in double perovskite structure was understood by correlating the electrical conductivity and thermoelectric power (S). S(T) curve of different samples was fitted with the proposed equation S(T)u2009=u2009S0+S1T+S3/2T3/2+S3T4 and each term has been interpreted in this paper.

Structural phase stability, magnetism and microwave properties of Co2FeO4 spinel oxide

Correlation between crystal structure and physical properties for Co2FeO4 spinel oxide are studied. There are two coexisting phases, Fe rich and Co rich spinels, for S80, S86, S100 samples. The S90 and S95 samples showed single phase nature. A small signature of second phase is noted for S95 sample from the temperature dependence of magnetization measurement. The single phase with single Curie temperature at about 453 K is confirmed for S90 sample. Interestingly, S95 sample showed minimum magnetic energy loss. The complex magnetic permittivity and dielectric permeability at 4.6 GHz and 7.2 GHz has been measured for all samples. There is a correlation between annealing temperature for the samples and measured electromagnetic properties.