We report here enhancement of ferromagnetism in pure ZnO upon thermal annealing with the ferromagnetic transition temperature Tc above room temperature. We observe a finite coercive field upto 300K and a finite thermoremanent magnetization upto 340K for the annealed sample. We propose that magnetic moments can form at anionic vacancy clusters. Ferromagnetism can occur due to either superexchange between vacancy clusters via isolated F+ centers, or through a limited electron delocalization between vacancy clusters. Isolated vacancy clusters or isolated F+ centers give rise to a strong paramagnetic like behaviour below 10K.

Enhancement of ferromagnetism upon thermal annealing in pure ZnO

Polycrystalline SrSnO3 compounds doped with 1, 3 and 5% of Cr was synthesized by simple chemical precipitation method and the effect of doping on structural, optical and magnetic properties was investigated. Powder X-ray diffraction analysis reveals the orthorhombic structure of pure and Cr doped SrSnO3 compounds. The appearance of metal oxide vibrations were investigated by Fourier transform infra red spectroscopy analysis. Presence of active Raman modes, Sr–O and Sn–O band vibrations were examined by Raman spectral analysis. The high degree of agglomeration in pure SrSnO3 sample and formation of rod like shape of particulate system in all the Cr doped samples was identified by Electron microscopy techniques. X-ray photoelectron spectroscopy analysis discloses the oxidation states of elements and presence of oxygen vacancy in the compounds. The intriguing violet–blue emission behavior of pure and Cr doped compounds due to interaction between O 2p state and Sn 5s energy levels was observed by photoluminescence spectral studies. The magnetization studies exhibit the diamagnetic property of pure SrSnO3 compound and doping of Cr3+ in Sr–Sn–O lattice drives the carrier induced exchange interactions which results ferromagnetic phase transition in all the Cr doped compounds. From the present investigation, tunability of dia to ferromagnetism with respect to the dopant concentration (Cr3+) in SrSnO3 system at room temperature leads the material for fabrication of magneto-optical and electronic devices.

Room temperature ferromagnetism in Cr doped SrSnO3 perovskite system

First-principles study of half-metallic properties of the Heusler alloy Ti2CoGe

In this paper, we report the synthesis of Fe containing strontium stannate (SrSnO3) nanoparticles by a facile cost-effective wet chemistry route using cetyltrimethyl ammonium bromide (CTAB) as a surfactant Thermogravimetric analysis together with differential scanning calorimetric data revealed the formation of SrSn(OH)6 as the initial compound, which led to the formation of SrSnO3 via three main endothermic dehydration cycles The X-ray diffraction patterns of the final compound revealed the formation of the orthorhombic phase of SrSnO3 with Pbnm symmetry, and exhibited the contraction of cell volume with increase in Fe content Raman spectra showed peaks at 220, 256, 306, 404, 452 and 561 cm−1, which corresponds to Sn–O and O–Sn–O band stretching The band gap values were found to be 417, 381 and 352 eV for the samples with 0, 2 and 4 at% Fe content, respectively The photoluminescence spectra also confirmed the red shift of band emission peak observed around 370 nm The relative permittivity was observed to be low and showed steady variation with temperature and Fe content The dielectric relaxation time was found to decrease with temperature and increase with Fe content The ac conductivity values were 323 × 10−8, 398 × 10−8 and 447 × 10−8 Ω−1 cm−1, and activation energy was found to be 022, 034 and 044 eV for pristine and Fe (2 and 4 at%) Conductivity analysis suggested the hopping of charge carriers in the crystal, as the possible mechanism for electric conduction

Fe(III) induced structural, optical, and dielectric behavior of cetyltrimethyl ammonium bromide stabilized strontium stannate nanoparticles synthesized by a facile wet chemistry route

Several cobalt-based Heusler alloys have been predicted to exhibit Weyl Semimetal behavior due to time reversal symmetry breaking. Co2TiGe is one of the predicted ferromagnetic Weyl semimetals. In this work, we report weak localization and small anomalous Hall conductivity in half-metallic Co2TiGe thin films grown by molecular beam epitaxy. The longitudinal resistivity shows semimetallic behavior. Elaborate analysis of longitudinal magnetoconductance shows the presence of a weak localization quantum correction present even up to room temperature and reduction in dephasing length at lower temperature. Negative longitudinal magnetoresistance is observed from 5 to 300 K, but at 300 K magnetoresistance becomes positive above 0.5 T magnetic field. The anomalous Hall effect has been investigated in these thin films. The measured anomalous Hall conductivity decreases with increasing temperature, and a small anomalous Hall conductivity has been measured at various temperatures which may be arising due to both intrinsic and extrinsic mechanisms.

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Weak localization and small anomalous Hall conductivity in ferromagnetic Weyl semimetal Co 2 TiGe

Structural, magnetic and semiconducting properties of Fe doped SrSnO3

Half metallic Co2TiGe-a theoretical and experimental investigation

HfO2 films were produced by sputter deposition in the substrate temperature (Ts) range of room temperature (RT)−300 °C and their structural, magnetic, and electrical properties were evaluated. The results indicate that the HfO2 films crystallize in the monoclinic structure and are oriented along the (−111) direction. Magnetization measurements (300–1.8 K) evidence their RT ferromagnetism. The effect of Ts is significant on the magnetic moment (M) and coercivity (Hc). M and Hc values enhanced with increasing Ts due to formation of oxygen vacancies. Increase in the temperature from 150 to 300 K decreases Hc without any transition, indicating that the Curie temperature of HfO2 films is higher than RT. Electrical measurements indicate that the HfO2 films are semiconducting.

Room temperature ferromagnetism in HfO2 films

The effect of antimony doping on the structural, magnetic, and electrical properties of transparent SrSn0.9Sb0.05Fe0.05O3 films synthesized by RF sputtering on oxidized Si and quartz substrates has been investigated. A reduction in electrical resistivity by two orders of magnitude compared to 5% Fe doped SrSnO3 film was observed. The electrical conductivity behavior has been analyzed using the Mott’s Variable range hopping model. The nature of magnetic ordering were investigated by field cooled (FC) and zero field cooled (ZFC) magnetization measurements. The applicability of models based on oxygen vacancies to explain the magnetic ordering present in the sample has been discussed.

Magnetic and transport properties of transparent SrSn0.9Sb0.05Fe0.05O3 semiconductor films

SrSn0.95Fe0.05O3 films were grown on oxidized silicon and quartz substrates by RF sputtering technique. The electronic transport and optical properties of the films were investigated. The temperature dependence of electronic conductivity has been analyzed quantitatively using Mott's small polaron hopping model in the temperature range Room Temperature (RT) −240 K and variable range hopping model in the temperature range 240-190 K.

G. Prathiba

Papers

Structural, magnetic and semiconducting properties of Fe doped SrSnO3

Half metallic Co2TiGe-a theoretical and experimental investigation

Room temperature ferromagnetism in HfO2 films

Magnetic and transport properties of transparent SrSn0.9Sb0.05Fe0.05O3 semiconductor films

The optical and electronic transport properties of SrSn0.95Fe0.05O3 films