Impact of Gd³⁺substitution on the structural, magnetic and electrical properties of cobalt ferrite nanoparticles

Abstract

In this work, we have focused on the influence of Gd 3+ substitution in structural, magnetic and electrical properties of cobalt ferrite synthesized by using sol-gel auto combustion method. The powder x-ray diffraction analysis reveals that the Gd-substituted cobalt ferrites crystallize in single phase spinel structure for lower concentrations of Gd 3+ , while a trace of GdFeO 3 appears as a minor phase for higher concentrations. Raman and Fourier transform infrared spectra confirm the formation of spinel structure. Furthermore, Raman analysis shows that the inversion degree of cobalt ferrite decreases with Gd 3+ doping. The field emission scanning electron microscopy images show that the substitution of small amount of Gd 3+ causes considerable reduction of grain size. Studies on magnetic properties reveal that the coercivity of Gdsubstituted cobalt ferrites enhances from 1265 Oe to 1635 Oe and the saturation magnetization decreases monotonically from 80 emu/g to 53.8 emu/g and the magnetocrystalline anisotropy constant increases from 5.8x10 5 erg/cm 3 to 2.23 x10 6 erg/cm 3 at 300 K. The electrical properties show that the Gd 3+ doped samples exhibit the high values of dielectric constant (616 at 100 Hz) and ac conductivity (4.83x10 -5 S/cm at 100 Hz) at room temperature. The activation energy is found to decrease from 0.408 to 0.347 eV in for the rise of Gd 3+ content. The impedance study 2 brings out role of bulk grain and grain-boundary towards the electrical resistance and capacitance of cobalt ferrite. Gd-substitution and nano size of cobalt ferrite enhance the electrical and magnetic properties which could ensure a higher memory storage capability. IntroductionSpinel ferrites with the general formula MFe 2 O 4 (M-Co, Ni, Mn and Zn etc.) are the most interesting magnetic oxides due to their superior electrical, magnetic and optical properties 1-8 .Among the spinel ferrites, cobalt ferrite is an attractive candidate due to its significant properties such as high coercivity, high electrical resistivity, moderate saturation magnetization, large magnetocrystalline anisotropy (~4x10 6 ergs/cm 3 ), good chemical stability and high Curie temperature (793 K) 9-16 . It is of significant technological interests due to its potential applications in targeted drug delivery systems 17, 18 , microwave devices 19, 20 , sensors 21 , catalysis 22, 23 and magnetic recording applications 9, 24 etc. Recently, the doping of small amount of trivalent rare earth cations in spinel ferrite has emerged as a promising strategy to improve the magnetic and electrical properties. Moreover, these properties are governed by the antiferromagnetic super exchange interaction between Fe 3+ -Fe 3+ ions; introducing small amount of trivalent rare earth (RE) ions into the spinel ferrite lattices will also induce RE 3+ -Fe 3+ interactions 25-30 . It is well known that the intrinsic properties of the spinel ferrite nanoparticles depend on the chemical composition and preparative methods 31, 32 . Spinel ferrites are prepared using several methods s...

Enhanced dielectric permittivity on yttrium doped cobalt ferrite nanoparticles

“…For instance, at 100 Hz and 1.0 kHz, ε are ∼ 200 and ∼ 83 , ∼ 998 and ∼ 320 for x = 0 and 0.04, respectively, Table 1 . Similar results have been reported for gadolinium doped cobalt ferrites nanoparticles prepared by sol-gel auto combustion method [14,16]. The observed high values of the dielectric constant at low frequencies and low values at high frequencies indicate large dispersion which is mainly due to the Maxwell-Wagner type of interfacial polarization [22,23] and is in good agreement with Koop's phenomenological [22]theory; i.e, the dispersion in due to the inhomogeneous double layer dielectric structure.…”

“…Nevertheless, doping cobalt ferrites with Cr 2+ , Mg 2+ , and Gd 3+ ions decrease the magnetic properties at room temperature [11,14]. However, signicant increase in dielectric properties of cobalt ferrite nanoparticles were achieved by doping with Gd 3+ ions [14,16] which were attributed mainly to space charge polarization and the presence of conducting phases on the insulating nanoparticles. On contrary, reduction in the dielectric permittivity nickel ferrite ceramic doped with Y 3+ ions have been reported in the literature [17].…”

“…For instance, doping with small amount of non-magnetic ions Zn 2+ , and Bi 3+ ions increases the saturation magnetization [810,15]. Nevertheless, doping cobalt ferrites with Cr 2+ , Mg 2+ , and Gd 3+ ions decrease the magnetic properties at room temperature [11,14]. However, signicant increase in dielectric properties of cobalt ferrite nanoparticles were achieved by doping with Gd 3+ ions [14,16] which were attributed mainly to space charge polarization and the presence of conducting phases on the insulating nanoparticles.…”

“…This uniques properties make cobalt ferrite suitable compound for several technological applications such as magnetic high-density digital recording media, microwave devices, chemical sensors, catalysis, ferrouid technology, target drug delivery systems and etc. [14]. It is well known that changes in cation distribution between tetrahedral A-and octahedral B -sites aect the structure and physical properties of cubic ferrites [57].…”

Synthesis and dielectric properties of Zn doped GdFeO3ceramics

“…In the present work, Gd based orthoferrite (GdFeO 3 ) has been undertaken to study its structural and dielectric properties. It is well known that the intrinsic properties of the materials depend on the chemical composition and preparative methods [4]. In our present work Zn doped GdFeO 3 is prepared by the standard Solid State Reaction method.…”