Carrier mediated ferromagnetism in Cr doped SrTiO3 compounds

Abstract

The carrier doped ferromagnetism in SrTiO 3 compounds has been investigated for the importance in the field of multiferroics and spintronics. Polycrystalline pure and Cr doped SrTiO 3 compounds were synthesized by glycol assisted sol-gel method. Powder X-ray diffraction (XRD) studies reveal the simple cubic perovskite structure of all the prepared compounds. The grain size and lattice strain of the compounds were estimated from the powder XRD pattern which evidences the incorporation of Cr in SrTiO 3 system. The local order and disorder parameter of the compounds was investigated by laser Raman spectroscopy. The change in particles to rod like surface morphology while increasing Cr doping concentration was examined by scanning electron microscope and transmission electron microscopy. The enhancement of oxygen vacancy while increasing Cr doping concentration in SrTiO 3 system and reduction in Ti 4? to Ti 3? states was identified by X-ray photoelectron spectroscopy. The UVVis absorption spectra evidence the distinctive shift of absorption edge exclusively for Cr doped SrTiO 3 compounds. Photoluminescence (PL) spectra of the compounds reveal defective states and decrease in PL intensity due to the influence of Cr in SrTiO 3 . Electron paramagnetic resonance analysis of Cr doped compounds reveals the paramagnetic nature of the dopants. The magnetization studies of all the prepared compounds emphasis carrier mediated diamagnetic to ferromagnetic phase transition in due with the presence of carriers induced by Cr. It is also evident that the highest dopant concentration of Cr in SrTiO 3 system exhibits reversal ferromagnetism. The enhancement of magnetization and ferromagnetic ordering has been understood in terms of carrier-mediated Ruderman-KittelKasuya-Yosida interaction theory. The present work also demonstrates the influence of surface morphology on the occurrence of ferromagnetism in Cr doped SrTiO 3 compounds.

Structural and optical properties of SrTiO3 nano material obtained by sol-gel method

“…The value of Eg is in the range 3.04 eV to 3.18 eV. This result is fairly consistent with the result that was announced by M. Muralidharan et al [10]. The band gap of prepared STO particles is very close to that of some photocatalytic materials such as TiO2.…”

“…All FTIR spectra of STO show the absorption band at 400-750 cm −1 , corresponding to the TiO 6 octahedron in the crystal, which reveals that the STO crystal structure started forming at 600 o C. However, the intensity of absorption peak significantly increased as temperature increased to above 900˚C. It is consistent with the result that was reported by M. Muralidharan group [10]. The XRD and FTIR results suggests that STO materials could be prepared by the sol-gel method and the optimized annealing temperature for the best quality of crystalline is in a range from 800˚C to 1000˚C.…”

“…• C -1000˚C. These results are consistent with the previous studies [10][11][12]. The particle size of samples was calculated from XRD pattern by using the Debye -Scherrer formula.…”

Weak room temperature ferromagnetism and ferroelectric behavior in sonochemically synthesized bismuth and iron codoped SrTiO 3 nanoparticles

“…2a). The undoped SrTiO 3 nanoparticles exhibit diamagnetic behavior which is expected due to the absence of unpaired electrons [9] doping, an S-shaped curve was obtained with slight coercivity of ∼55 Oe suggesting very weak ferromagnetism in the sample. Since the dopant ion in this case in nonmagnetic, the weak ferromagnetism observed cannot be attributed to magnetic impurities or clustering of magnetic species as reported in case of Mn doped SrTiO3 [16].…”

“…Nevertheless, ferroelectricity has been observed in SrTiO 3 with chemical doping and application of mechanical stress and electric field [3][4][5][6]. There are also some reports on transition metal ion doped SrTiO 3 :M (M ¼Mn, Fe, Cr) which exhibits ferromagnetic behavior though the bulk material is diamagnetic [7][8][9]. However, reports on multifunctional SrTiO 3 material exhibiting both ferromagnetic and ferroelectric properties are scarce [10].…”