Elsevier

Materials Research Bulletin

Volume 49, January 2014, Pages 338-344
Materials Research Bulletin

Effect of Eu–Ni substitution on electrical and dielectric properties of Co–Sr–Y-type hexagonal ferrite

https://doi.org/10.1016/j.materresbull.2013.09.012Get rights and content

Highlights

  • Single phase nanostructured Sr2Co2−xNix EuyFe12−yO22 were synthesized by the microemulsion method.

  • The materials show semiconducting behavior.

  • The high resistivity makes these materials useful for high frequency applications.

  • The Curie temperature decreases with the substituents.

Abstract

Single phase nanostructured Eu–Ni substituted Y-type hexaferrites with nominal composition Sr2Co2−xNix EuyFe12−yO22 (x = 0.0–1, y = 0.0–0.1) were synthesized by the normal microemulsion method. X-ray diffraction (XRD) technique was employed for phase analysis and indexing of each pattern corroborates that well defined Y-type crystalline phase is formed. It is observed that DC resistivity enhanced which is accredited to room temperature resistivity differences of dopant and host ions. The hopping of electrons and jumping of holes are responsible for conduction below Curie temperature (TC), whereas above Curie temperature is due to polaron hopping. The decrease in TC may be due to the fact that Eu–Fe interactions on the B sites are weaker than Fe–Fe interaction. The dispersion in the dielectric constant ɛ′(f) favor the occurrence of peaks in the tan δ(f). The extraordinary values of resistivity and small dielectric loss make these materials pre-eminent contestant for high frequency applications.

Introduction

Ferrites have continued to allure the attention of researchers over the years. As magnetic materials, ferrites cannot be replaced by any other magnetic material because they are relatively inexpensive and stable [1]. The physicochemical properties of particles in the size range of 1–100 nm are dramatically different from those of their bulk counterparts [2]. Strontium hexaferrites are extensively studied due to its perfect chemical stability, good thermal durability, corrosion resistivity, unique electrical and magnetic properties, has extensive applications in recording devices [3], magneto optical and microwave devices [4]. These materials cover a wide field of technological applications, from microwave to radio frequencies, due to its high electrical resistivity [5]. These materials are also used in transformer core, high quality filters and operating devices [6] due to the rapid development of information and communication technology. As more components are integrated in smaller space so electromagnetic compatibility and anti-electromagnetic interference (EMI) become one of the most challenging problems in electronic products. The importance of special surface mount components to resist EMI in integrated circuit is driven up that promotes a great demand of the chip soft-magnetic components (including multi-layer chip inductors (MLCI) and chip electromagnetic interference filters) in hyper frequency applications [7], [8]. The study of the dielectric properties and DC electrical resistivity reveals valuable information about the behavior of localized and free electrical charge carriers. This leads to a better understanding of the mechanism of electrical conduction. The physical properties of ferrites are controlled by the preparation conditions chemical composition, sintering temperature and time, type and amount of substitutions [9].

Gorter [10] made the first attempt to determine the position of the magnetic ions and orientations of the spins in the crystal lattice by considering exchange interactions. It was observed that the spins are collinear in the basal plane particularly in Y-type hexagonal structure having space group (R3m). The Y-type hexagonal ferrites structure built up as a superposition of S and T blocks. The unit cell is composed of the sequence STSTST including three formula units. Each formula unit consists of two layered spinel S block and four-layered antiferromagnetic T block [11]. The metallic cations are distributed among six sublattices [12].

Y-type can be synthesized by annealing at relatively lower temperatures of 900–1100 C° as compared with other hexaferrites [13]. The traditional spinel ferrites cannot provide high initial permeability in hyper-frequency range because of their low FMR frequency for MLCI applications. But the Y-type hexagonal ferrites exhibit excellent properties with high cut-off frequency, high and tunable initial permeability in high frequency range. Soft Y-type hexagonal ferrites have much higher cut-off frequency than spinel ferrites due to the planar magnetic anisotropy [14], [15].

Chief focus of the present investigation is to study the influence of Eu–Ni substitution in Sr2Co2Fe12O22 system on electrical and dielectric properties, in view of this it is thought that the systematic investigation of electrical transport properties such as electrical resistivity and dielectric properties would also be very much essential and advantageous for high frequency application. The study would also elucidate the conduction mechanism in these materials. The present investigation is designed to examine the electrical properties as function of temperature and composition.

Section snippets

Synthesis procedure

The Y-type hexaferrite samples with nominal composition Sr2Co2−xNix EuyFe12−yO22 (x = 0.0–1, y = 0.0–0.1) were prepared by the normal Microemulsion method. The analytical regents Fe(NO3)3·9H2O (Riedel-de Haen, 97%), Co(NO3)2·6H2O (Merck, >99%), NiCl2.6H2O (Merck, 99%), Sr(No3)2 (Merck, 99%), Eu2O3 (Merck, 99%) (cetyltrimethyl ammonium bromide) CTAB (Merck, 97%) as a surfactant, NH3 (Fisher Scientific, 35%) as a precipitating agent and methanol (Merck, 99%) as washing agent were used to synthesize

Structural analysis

Typical X-ray diffractions patterns of Eu–Ni substituted Sr2Co2Fe12O22 samples at room temperature are shown in Fig. 1 and X’pert highscore was used to index the XRD patterns. The indexing of each pattern indicates that the well defined Y-type crystalline phase is formed. Enhanced intensity of peaks which is measure of improved crystalline phase suggests that Eu–Ni ions in the nominated substitution range are entirely dissolved in the Sr–Co–Y crystal lattice.

Minor deviations are observed in the

Conclusions

Nanostructured and single phase Y-type hexaferrites were synthesized by the normal microemulsion technique. The measured values of activation energies in the paramagnetic region (E2) are greater than 0.40 eV which obviously propose that the conduction is due to polaron hopping. The dielectric constant and loss factor vs frequency follow the Maxwell Wagner model with several resonance peaks at higher frequencies indicating anomalous dispersion. The enhancement in resistivity and small dielectric

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