Structural and magnetic properties of α-Fe2-xGaxO3 system in the range of low Ga content (x = 0.28–0.60) have been discussed in the present work. The samples with nanometer grain size have been prepared by coprecipitation of the metal hydroxides at high alkaline medium. The as prepared samples have been annealed at 800 °C under vacuum. Synchrotron X-ray diffraction pattern of the samples has been used to confirm rhombohedral structure with space group R3¯C, along with extra phase less than 2% of the rhombohedral phase. Raman active phonon modes are consistent with the spectrum of rhombohedral structure in α-Fe2O3. Raman spectra revealed structural disorder at microscopic level due to doping effect. The samples of α-Fe2-xGaxO3 system exhibited ferromagnetic properties and magnetization showed increasing trend with the increase of Ga content. Low temperature x-ray diffraction pattern and magnetization have been studied for the sample with x = 0.6 to test the correlation between structure and ferromagnetic parameters.

We have studied current-voltage (I-V) characteristics of α-Fe1.64Ga0.36O3, a typical canted ferromagnetic semiconductor. The sample showed a transformation of the I-V curves from linear to non-linear character with the increase of bias voltage. The I-V curves showed irreversible features with hysteresis loop and bi-stable electronic states for up and down modes of voltage sweep. We report positive magnetoresistance and magnetic field induced negative differential resistance as the first time observed phenomena in metal doped hematite system. The magnitudes of critical voltage at which I-V curve showed peak and corresponding peak current are affected by magnetic field cycling. The shift of the peak voltage with magnetic field showed a step-wise jump between two discrete voltage levels with least gap (ΔVP) 0.345(± 0.001) V. The magnetic spin dependent electronic charge transport in this new class of magnetic semiconductor opens a wide scope for tuning large electroresistance (∼500-700%), magnetoresistance (70-135 %) and charge-spin dependent conductivity under suitable control of electric and magnetic fields. The electric and magnetic field controlled charge-spin transport is interesting for applications of the magnetic materials in spintronics, e.g., magnetic sensor, memory devices and digital switching.

Li0.5Mn0.5Fe2O4 ferrite has been prepared by solid state sintering route. XRD pattern showed single phased cubic spinel structure. The samples exhibited typical character of plastoferrite with ring shaped surface microstructure. New feature observed in the present ferrite is the frequency activated conductivity transition from semiconductor to metallic state above 800 K. The increase of conductivity with frequency in the semiconducting regime follows Jonscher power law, while decrease of conductivity in metallic regime obeys Drude equation. The conductivity in semiconductor regime has been understood by hopping mechanism of localized charge carriers among the cations in B sites of cubic spinel structure. At higher temperatures, overlapping of electronic orbitals from neighbouring ions and free particle like motion of lighter Li+ ions among interstitial lattices contributed metallic conductivity. The samples provided evidence of localized nature of the charge carriers at lower temperatures and increasing delocalized character with the increase of measurement temperature. From application point of view, such ferrites behave as semiconductor at low temperature and allow electromagnetic wave to pass through, but transform into a metallic reflector with negative dielectric constant at high temperature.

No abstract

We report the structural phase characterization and magnetic properties of the chemical routed α-Fe2−xGaxO3 system (x: 0.28–0.60) after annealing at 800 °C in air.