S. Philip Raja

Room temperature ferromagnetism in vacuum annealed ZnFe2O4 nanoparticles

We report room temperature ferromagnetism in vacuum annealed ZnFe2O4 (ZFO) nanoparticles. Upon vacuum and air annealing, ZFO nanoparticles show ferro and paramagnetic behavior, respectively. The well defined sextets along with doublet seen in the Mossbauer spectra confirms ferromagnetic coupling in vacuum annealed ZFO. After reannealing in air, the magnetization of vacuum annealed sample reduces from 62 to 1.5 emu/g. Both Mossbauer and micro-Raman results suggest that oxygen vacancies generated during vacuum annealing causes cation redistribution between the interstitial sites resulting in magnetic ordering. Our results show a unique possibility of switching the magnetic properties of ZFO between paramagnetic to ferromagnetic.

Investigation of magnetic behaviour of Ni–Fe–O prepared by the solid state method

Polycrystalline Fe doped NiO was prepared by the solid state method with the aim of exploring its suitability as a functional material for spintronics applications. Phase pure samples (up to 2% doping of Fe) as evident from x-ray diffraction were characterized to investigate the magnetic, electric and dielectric properties. Magnetic measurements using the vibrating sample magnetometer clearly reveal ferromagnetic behaviour at room temperature. The activation energies of the doped samples, determined from impedance spectroscopy, were found to be relatively higher than that of undoped NiO. It is also observed that Fe doping has no significant effect on the dielectric properties of the samples. Thermogravimetric analysis, carried out to find the Curie temperature (TC), leads to a remarkable insight into the observed ferromagnetism by identifying the presence of secondary phase NiFe2O4.

Investigation of the Less Oxygen Deficient SrFeO3‐δ

Perovskite type SrFeO3 is a suitable candidate for gas sensors and catalytic applications. It is very difficult to stabilize the stoichiometric SrFeO3, which is highly unstable because of the presence of Fe4+ ions that leads to the oxygen vacancies (δ) in order to maintain charge equilibrium. For δ = 0, 0.13, 0.27 and 0.5, it takes SrFeO3, SrFeO2.87, SrFeO2.73 and SrFeO2.5 phases respectively. The oxygen vacancy plays an important role in determining its structural and electronic properties. Nanocrystalline SrFeO3 has been prepared by thermal decomposition method and its structural, morphological, magnetic and electrical properties are analyzed.

Synthesis and Characterization of BiMn2O5 Ceramics

BiMn 2 O 5 , prepared by high energy ball milling of precursor oxides followed by sintering at 900° C for 24 h, has been investigated for its magnetic and electrical properties. The XRD pattern reveals orthorhombic phase with Pbam space‐group. Magnetization measurements show a paramagnetic behaviour at room temperature with a Neel transition at 40 K. Electrical conductivity studies show room temperature resistivity value around 9×10 5 Ω cm .

Synthesis and Characterization of BiMn2O5Ceramics

BiMn 2 O 5 , prepared by high energy ball milling of precursor oxides followed by sintering at 900° C for 24 h, has been investigated for its magnetic and electrical properties. The XRD pattern reveals orthorhombic phase with Pbam space‐group. Magnetization measurements show a paramagnetic behaviour at room temperature with a Neel transition at 40 K. Electrical conductivity studies show room temperature resistivity value around 9×10 5 Ω cm .

Synthesis and Characterization of BiMn[sub 2]O[sub 5] Ceramics

BiMn 2 O 5 , prepared by high energy ball milling of precursor oxides followed by sintering at 900° C for 24 h, has been investigated for its magnetic and electrical properties. The XRD pattern reveals orthorhombic phase with Pbam space‐group. Magnetization measurements show a paramagnetic behaviour at room temperature with a Neel transition at 40 K. Electrical conductivity studies show room temperature resistivity value around 9×10 5 Ω cm .

Room Temperature Ferromagnetism in Nanocrystalline Ce1−xFexO2

We report room temperature ferromagnetism in Fe‐doped CeO2 powders prepared by chemical coprecipitation method. Analysis of Ce1−xFexO2 using XRD reveals single phase formation for the samples with x≤0.05. EDX results confirm the near stoichiometry of the samples with a nominal variation mainly due to the random alloying of the dopants. FE‐SEM micrographs clearly illustrate the nanocrystalline nature of the samples with a uniform particle size distribution. M‐H curve of undoped CeO2 and Ce0.97Fe0.03O2 recorded at room temperature using vibrating sample magnetometer (VSM) indicate a paramagnetic like behavior. However, room temperature ferromagnetism is clearly observed in Ce0.95Fe0.05O2, which is expected to originate from a combination effect of oxygen vacancies and transition metal doping. The experimental results provide direct evidence for the role of oxygen vacancies in mediating the ferromagnetic ordering.