S. P. Pareek

200 MeV Ag+15 ion irradiation-induced modifications in structural, magnetic and dielectric properties of nanoparticles of Cu0.2Zn0.8Fe2O4 ferrite

The present investigation aims at studying the effect of swift heavy ion irradiation on the structural, magnetic and dielectric properties of the nanocrystalline Cu0.2Zn0.8Fe2O4 spinel ferrite. The sample was synthesised using the sol–gel technique and then irradiated with the 200 MeV Ag+15 ion beam. The Rietveld profile refinement of the X-ray diffraction patterns confirmed the cubic spinel structure of samples. The spherical morphology revealed through transmission electron microscopy images was consistent with the crystalline diameter. The overall magnetic behaviour pointed towards superparamagnetic relaxation at room temperature along with the significant increase in saturation magnetisation, coercivity and blocking temperature after irradiation. This could be attributed to the slight increase in the particle size and ion-induced modifications on the surface states of the nanoparticles. The enhancement in dielectric constant and loss tangent after irradiation could be attributed to the available Fe+2 ↔ Fe+3 and/or Zn+2 ↔ Zn+3 ion polarisation at the octahedral site, especially on grain boundaries of the sample.

Effect of 200 MeV Ag+15 ion irradiation on magnetic and dielectric properties of nanocrystalline Zn–Cr ferrite

Nanocrystalline samples of ZnCr0.4Fe1.6O4 ferrite were synthesized by the advanced sol–gel method to investigate the effect of 200 MeV Ag+15 ion irradiation on the cation distribution, magnetic and dielectric properties. Rietveld profile refinement of the X-ray diffraction (XRD) patterns confirms the single-phase cubic spinel structure of the specimens. The irradiated sample retains the cubic spinel structure with a slight increase in the lattice parameters and the average crystallite size. Temperature- and field-dependent dc magnetization studies show an appreciable enhancement in the saturation magnetization and blocking temperature of the irradiated samples, which could be attributed to the slight increase in the particle size due to the heat evolved during irradiation. Subsequently, the rearrangement of cations in the lattice structure and the ion-induced modifications on the surface states of the nanoparticles could be accountable. The room temperature dielectric constant and the loss tangent in the frequency range 75 kHz–10 MHz revealed the normal frequency dispersion. The increase in ϵr and tan δ on irradiation could be attributed to the slight crystal growth and hence the availability of the sufficient number of Fe2+ and/or Zn3+ ions particularly at the octahedral site on the grain boundaries, showing a fair agreement with the magnetization results.

Retraction Note to: Sol–gel synthesized high anisotropy magnetic nanoparticles of NiCrxFe2−xO4

The nanoparticles of NiCrxFe2−xO4 were synthesized through sol–gel reactions involving nitrates of Ni, Cr and Fe in an aqueous medium containing citric acid. The cubic spinel structure in single phase with nanometric crystallite size of ~5 nm, the spherical morphology and magnetic relaxations were examined through XRD, TEM and Mossbauer techniques. The abnormal occurrence of finite remanance (Mr) and coercivity (Hc) resulted in the room temperature dc magnetization measurements for the small particles authenticate the ferrimagnetic regime, as proposed by the room temperature Mossbauer results of the samples, with a proximate superparamagnetic regime still at lower particle volumes. This could be attributed to the antiferromagnetic spin interactions of chromium ions at octahedral sites and subsequently the over-occupancy of the rest of the cations at tetrahedral sites. In justification to this, the magnetocrystalline anisotropy constant, K, is estimated to have value relatively high of the order of 107 erg/cm3 at room temperature for all studied concentrations.

Study of cation distribution in Cu-Zn ferrites

Series of nanocrystalline Cu1-xZnxFe2O4 (x=0.2, 0.4, 0.6 and 0.8) spinel ferrites were synthesized using advanced sol-gel technique. The XRD measurements confirm the formation of cubic spinel structure in single phase for the entire sample. The average particle sizes of 14-18 nm with lattice parameter ranges from 8.38A to 8.52A were estimated. Cation distribution over the two sites of nanocrystalline Cu1-xZnxFe2O4 series, estimated from X-ray diffraction measurements is reported. The lattice parameter ‘a’ is found to be increased with increase in Zn concentration, which is attributed to the larger ionic radius of Zn compared to that of Cu.

Dielectric behaviour of nanocrystalline Cu0.2Ni0.8Fe2O4 ferrite

Nanocystalline Cu0.2Ni0.8Fe2O4 of average particle size 3 nm was synthesized through chemical coprecipitation method followed by annealing at various temperatures. The formation of cubic spinel structure in single phase and the crystallite growth was confirmed using XRD. The dielectric behavior as a function of frequency in the range 75 kHz to 10 MHz was studied at room temperature. Both dielectric constant (e′) and the loss factor (tanδ) decreases with frequency for all samples. This decrease in the values could be explained on the basis of available ferrous, i.e. Fe2+, ions at octahedral sites such that beyond a certain frequency of applied electric field the electronic exchange between the ferrous and ferric ions i.e. Fe2+↔Fe3+ cannot follow the applied alternating electric field.

TEMPERATURE DEPENDENT DIELECTRIC BEHAVIOR OF NANOCRYSTALLINE Ca FERRITE

Dielectric behaviour of Nanocrystalline CaFe2O4 ferrite synthesized by advanced sol- gel method has been investigated as a function of frequency at different temperatures. Rietveld profile refinement of the XRD pattern confirms formation of cubic spinel structure of the specimen.The dispersion in dielectric behavior of CaFe2O4ferrite sample has been observed in the temperature range of 100-250˚C as a function of frequency in the range 75 kHz to 10 MHz Both the real value of dielectric constant (ɛ′) and the dielectric loss factor (tanδ) decrease with frequency. This decrease in the values of ɛ′ and tanδ could be explained on the basis of available ferrous, i.e. Fe2+, ions on octahedral sites such that beyond a certain frequency of applied electric field the electronic exchange between the ferrous and ferric ions i.e. Fe2+↔Fe3+ cannot follow the applied alternating electric field.

Dielectric Behavior of Nano sized Particles of Zn‐Cr Ferrite

Dielectric behavior of nanosized ZnCrxFe2−xO4 particles with x = 0.2, 0.4, 0.6 and 0.8, synthesized using sol‐gel method have been studied. The XRD patterns confirm formation of single phase cubic spinel structure of the specimens. The dielectric behavior of all the samples has been studied at 300 K as a function of frequency in the range 75 kHz to 10 MHz. Both the real value of dielectric constant (e) and the dielectric loss factor (tanδ) decreases with frequency respectively for all the samples. This decrease in the values could be explained on the basis of available ferrous, i.e. Fe2+, ions on octahedral sites such that beyond a certain frequency of applied electric field the electronic exchange between the ferrous and ferric ions i.e. Fe2+↔Fe3+ cannot follow the applied alternating electric field. Also, a gradual reduction in both e and tanδ observed as Cr concentration increases.

Dielectric Behavior of Bulk and Nanocrystalline Zn‐Mn Ferrite

This paper reports the synthesis of bulk sized Zn0.8Mn0.2Fe2O4 particles by solid state method followed by high energy ball milling at different times yielding nannocrystalline samples of different sizes. The dielectric behavior of the samples has been studied at 300 K as a function of frequency in the range 75 kHz to 10 MHz. Both the real value of dielectric constant (e′) and the dielectric loss factor (tanδ) decreases with frequency respectively for the three samples. Also the reduction in the value of e′ and tan δ for the ball milled samples is attributed to the least possibility of occurrence of Fe2+ ions at the octahedral site as size reduces.

Synthesis and size dependent magnetic behaviour of nanocrystalline Cu0.2Ni0.8Fe2O4 ferrite

Particle size has significant effect on the magnetic properties of nano‐particles. Nano‐particles of Cu‐Ni ferrite have been synthesized by the co‐precipitation method. Different particle sizes (3nm‐9 nm) were obtained by annealing the prepared samples at various temperatures. The specimens characterized using XRD confirmed the formation of cubic spinel structure. The samples show typical superparamagnetic behaviour above blocking temperature. The particle size increases with increasing the annealing temperature. The saturation magnetization & blocking temperature increases with particle size which is characteristic of superparamagnetism. The hysteresis curves show reduction in saturation magnetization in the case of nanoparticles as compared to their bulk counterpart, which have been explained on the basis that the magnetic moments in the surface layers of a nanoparticle are in a state of frozen disorder. However the saturation magnetization increases with particle size, which is the characteristic prope...