Dielectric, Complex Impedance, and Electrical Transport Properties of Erbium (Er³⁺) Ion-Substituted Nanocrystalline, Cobalt-Rich Ferrite (Co_1.1Fe_1.9–xEr_xO₄)

Abstract

Erbium (Er 3+ ) substituted nanocrystalline, cobalt-rich ferrites, which can be represented chemically as Co 1.1 Fe 1.9−x Er x O 4 (CFEO; x = 0.0−0.2), were synthesized by the sol−gel autocombustion method. The structural, dielectric, and electrical transport properties of CFEO were investigated in detail. CFEO materials crystallize in a spinel cubic structure for x ≤ 0.10; formation of orthoferrite (ErFeO 3 ) secondary phase was noted for x ≥ 0.15. Microstructural and compositional studies revealed the formation of spherical, elongated grains with stoichiometric presence of Co, Fe, Er, and O. The dielectric constant (ε′) dispersion fits to the Debye's function for all CFEO ceramics. The relaxation time and spread factor obtained from ε′ dispersion are ∼10 −3 s and ∼0.50 (±0.10), respectively. The complex impedance analyses confirm a graininterior mechanism contributing to the dielectric properties. Semiconducting behavior and small polaron conduction mechanism were evident in electrical transport properties of CFEO materials.

Effect of Molybdenum Incorporation on the Structure and Magnetic Properties of Cobalt Ferrite

“…Cobalt ferrite CoFe2O4 (CFO), one among these spinel ferrites, is the most useful hard ferrimagnetic material, which exhibits unique properties such as strong spin-orbit (L-S) coupling, high Curie temperature, high coercivity, high magneto-crystalline anisotropy, moderate saturation magnetization, large Kerr effect and Faraday rotation, good mechanical hardness and chemical stability. [1][2][3][4][5][6][7] Cobalt ferrite based materials find attractive applications in microwave and spintronic devices, solar cells, magnetostrictive sensors, drug delivery, transducers, actuators, lithium batteries, super capacitors and memory devices for computers. [1][2][3][4][5][6][7][8][9][10][11][12] Currently, nanoparticles and nano-architectures of CFO-based materials are gaining tremendous interest in view of their ability to exhibit tunable electrical and magnetic properties, which could be exploited in numerous technological applications.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12] Currently, nanoparticles and nano-architectures of CFO-based materials are gaining tremendous interest in view of their ability to exhibit tunable electrical and magnetic properties, which could be exploited in numerous technological applications. 2,3,8,10 Furthermore, higher values of magnetostriction make CFO a potential candidate material for 'strain sensor and actuator' applications. 11 Cobalt ferrites can be combined with a piezoelectric/ferroelectric material resulting in the multiferroic/magnetoelectric hetero-structures for application in multifunctional and tunable magneto-electronic devices.…”

“…For instance, partial substitution of Fe 3+ by rare earth (RE) ion, such as Er, Dy, La, Nd, Ho, leads to structural distortion in spinel structure which in turn induces strain and significantly modifies the electrical and dielectric properties. 2,6,9,12,16,17,19,[26][27][28] In addition, it has been reported in the literature that inclusion of transition metal (TM) ion, such as Zn, Cu, Co and Cd, in ferrites increase the dielectric constant due to the formation of excess Fe 2+ which eventually increase the hopping of electrons between Fe 2+ and Fe 3+ . 17,21,28 Recently, substitution for Fe 3+ in spinel ferrites has been gaining tremendous importance to design materials for utilization in high-density magnetic recording, enhanced memory storage, magnetic fluids, and catalyst applications.…”

“…17,21,28 Recently, substitution for Fe 3+ in spinel ferrites has been gaining tremendous importance to design materials for utilization in high-density magnetic recording, enhanced memory storage, magnetic fluids, and catalyst applications. 2,6,9,[12][13][14][15][16][17][18][19][26][27][28] In general, the chemical and physical nature of the ion/dopant into CFO matrix allows tuning the final magnetic, dielectric and electrical characteristics. [13][14][15][16][17][18][19][20][21][22][23][24][25] Specifically, the degree of modification that can result in the properties and phenomena of CFO depends on the ionic radius, the electronic configuration of the substituting ion, its site preference (A versus B site), and the extent of distribution at the specific sites within the spinel structure.…”

“…It has been already recognized that, among many possible ways of engineering the advanced functional materials based on ferrites, doping with different RE/TM-ions is a well-adopted, straightforward and versatile way to tune the structure and properties. 2,5,6,9,12,[16][17][18][19][20] Depending on the ionic size and concentration, incorporation of RE/TM-ions in spinel ferrite results in an improved dielectric constant, increase in resistivity and a decrease in dielectric and magnetic losses. 2,5,[16][17][18][19][20] However, understanding the effect of a refractory metal, such as Mo in this case, incorporation on the structure and the extent to which the electrical, magnetic and dielectric properties of CFO can be tuned is of primary interest in this work.…”