Room-temperature ferromagnetism in Fe-doped PbTiO3 nanocrystals

Journal of Applied Physics

Thakur

et al. 2008

High resistivity in nanostructured Pb͑Fe 0.012 Ti 0.988 ͒O 3 system prepared by using polyvinyl alcohol ͑PVA͒ in chemical route is observed. The PVA acts as a surfactant to limit the particle size. The Fe substitution for Ti controls the chemical stoichiometry and reduces the lattice distortion, i.e., c / a ratio, and hence the transition temperature reduces with Fe content. The phase structure, morphology, particle size, dc resistivity, and dielectric and magnetic properties of Pb͑Fe 0.012 Ti 0.988 ͒O 3 nanoparticles have been characterized by x-ray diffraction, transmission/ scanning electron microscopy, source meter, LCR meter, and vibrating sample magnetometer. The results indicate that the nanosize particles have high resistivity, which improves the dielectric constant at high-frequency region and increases magnetization of the specimens. The observed variable-range-hopping conduction mechanism indicates that Fe doping leads to the occurrence of local defect states in the PbTiO 3 lattice. The dispersionless dielectric properties with low loss are observed up to 15 MHz. The dielectric properties are improved than those obtained by the conventional process. The initial permeability values do not exhibit much variation up to ferromagnetic transition temperature after which it falls sharply. The large value of saturation magnetization is observed at room temperature.

Section: Methodscontrasting

confidence: 52%

Section: Introductionmentioning

confidence: 99%

Resistivity dependent dielectric and magnetic properties of Pb(Fe0.012Ti0.988)O3 nanoparticles

Journal of Applied Physics

Thakur

et al. 2008

“…This value of coercive field is very small as compared to some Pb͑Fe, Ti͒O 3 system of nanoparticles. 9,15 The similar behavior was also found in Pb͑Fe, W͒TiO 3 system of thin film. 16 It is reported that the spin canting due to small distortion between Fe 3+ -O-Fe 3+ spins, results in weak ferromagnetism.…”

supporting

confidence: 65%

Ferromagnetism and ferroelectricity in highly resistive Pb0.7Sr0.3(Fe0.012Ti0.988)O3 nanoparticles and its conduction by variable-range-hopping mechanism

Singh

Applied Physics Letters

et al. 2008

The enhancement in ferromagnetism and ferroelectricity at room temperature for Pb 0.7 Sr 0.3 ͑Fe 0.012 Ti 0.988 ͒O 3 ͑PSFT͒ nanoparticles is proved by magnetization and polarization hysteresis loop. The x-ray diffraction and micrograph show that the PSFT nanoparticles have distorted tetragonal single phase, and their average particle's size is 8 nm. The effect of Sr content reduces the particle size, and hence the multiferroic system becomes more resistive, which dominates the superparamagnetic/paraelectric relaxation. The variable-range-hopping conduction mechanism explained the high resistivity of PSFT nanoparticles, which suggests that the room temperature movement of electrons involves short-range order through defect states. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2973400͔The emerging trend of size reduction in nanomultiferroic system becomes more interesting in its field. In fact, the small nanomultiferroic systems have remarkable electric ͑i.e., spontaneous polarization͒ as well as magnetic ͑i.e., saturation magnetization͒ orders, which may be due to the short-range movement of electrons within the Fermi gap, and thus increase resistivity. These electromagnetite nanoparticles are used in data-storage media, 1 spintronic devices, 2 and multiple-stage memories. 3 The most studied multiferroic systems of BiFeO 3 have low resistivity, 4 which results in weak ferromagnetism 5 and small polarization at room temperature. 6 Li et al. 7 reported the low resistivity in BiFeO 3 system, i.e., dependent on oxygen vacancies, low valence Fe ion due to their nonstiochiometric behavior and incomplete charge compensation, which may effect the distortion of the lattice. Rossiter et al. 8 reported that the highly resistive magnetoelectric semiconductor attributes short-range interaction between the conduction and the localized spin electrons, which are highly disordered and contribute weak superparamagnetic/paraelectric relaxation. In our previous work of Fe-doped PbTiO 3 nanoparticles, 9 the effect of polyvinyl alcohol ͑PVA͒ to reduce the particle size, which resulted in an increase in resistivity and improvement in ferromagnetism, was observed. The reported value of resistivity was in the order of 10 10 ⍀ cm, which is higher than other multiferroic systems such as BiFeO 3 . The resistivity of Fedoped PbTiO 3 system can further increase by reducing particle size with Sr substitution. Pontes et al. 10 reported the effect of Sr doping in PbTiO 3 to reduce grain size because the Sr content attributes lower grain-growth rates due to the slower diffusion of Sr 2+ with Pb 2+ ion. The substitutions of Sr at Pb site and Fe at Ti site may provide relaxation stability and interesting transport properties. In literature, 11,12 different stabilized relaxation processes were studied with varying temperature by a variable-range-hopping ͑VRH͒ conduction mechanism, which was employed when the conduction band is absent, and the extended states are far away from the Fermi level.In this letter, we report the enhanced ferromagne...

“…We have observed M s Ϸ 41.6 ϫ 10 −3 emu/ g ͑0.52 B / Fe͒ and H c ϳ 125 Oe for the specimen. The observed value of saturation magnetization is significantly higher than M s Ϸ 0.8ϫ 10 −3 emu/ g ͑0.01 B / Fe͒ reported by Ren et al 10 for their hydrothermal processed Fe doped nanocrystals ϳ100 nm using polyethylene glycol ͑PEG͒ as a surfactant. Improvement in ferromagnetic properties is due to the smaller particle's sizes in our specimens.…”

mentioning

confidence: 54%

“…Palkar and Malik 9 reported the conversion of a ferroelectric PbTiO 3 to a magnetoelectric system by partially substituting Ti with Fe. Ren et al 10 observed room temperature ferromagnetism in Fe-doped PbTiO 3 nanocrystals prepared by hydrothermal method using polyethylene glycol as a surfactant. However, further improvement in magnetic properties of Fe-doped PbTiO 3 is required to realize its actual use in magnetoelectric device applications.…”

mentioning

confidence: 99%

Improved dielectric and ferromagnetic properties in Fe-doped PbTiO3 nanoparticles at room temperature

Applied Physics Letters

Negi

2008

Fe-doped PbTiO 3 nanoparticles have been synthesized by chemical route using polyvinyl alcohol as a surfactant. The results indicate that the dielectric constant and magnetization value of these nanoparticles depends upon their size and Fe dopents. The x-ray diffraction analysis, and transmission and scanning electron microscopies show that the particle's sizes in the specimens lie in the range of 19-30 nm. It is observed that the magnetization is enhanced with reduction in particle size. The largest value of saturation magnetization ͑M s = 41.6ϫ 10 −3 emu/ g͒ is observed for 1.2 mol % Fe dopents. Dielectric constant and dielectric losses are controlled up to 15 MHz at room temperature.