Synthesis and spectroscopic characterization of copper zinc aluminum nanoferrite particles

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Highlights

  • Basic unit of (Zn1xCux)(AlxFe2x)O4 is made up of octahedral and tetrahedral units.

  • EPR spectra at low Cu content is dominated by Fe(III) and higher Cu content is dominated by Cu(II) only.

  • SAED indicating that crystallinity increases with increase of Cu/Al composition.

  • Non linear optics measurements indicating that the compound is good potential material for optical limiting applications.

Abstract

Copper doped zinc aluminum ferrites CuxZn1x.(AlxFe2x)O4 are synthesized by the solid-state reaction route and characterized by XRD, TEM, EPR and non linear optical spectroscopy techniques. The average particle size is found to be from 35 to 90 nm and the unit cell parameter “a” is calculated as from 8.39 to 8.89 Å. The cation distributions are estimated from X-ray diffraction intensities of various planes. The XRD studies have verified the quality of the synthesis of compounds and have shown the differences in the positions of the diffraction peaks due to the change in concentration of copper ions. TEM pictures clearly indicating that fundamental unit is composed of octahedral and tetrahedral blocks and joined strongly. The selected area electron diffraction (SAED) of the ferrite system shows best crystallinity is obtained when Cu content is very. Some of the d-plane spacings are exactly coinciding with XRD values. EPR spectra is compositional dependent at lower Al/Cu concentration EPR spectra is due to Fe3+ and at a higher content of Al/Cu the EPR spectra is due to Cu2+. Absence of EPR spectra at room temperature indicates that the sample is perfectly ferromagnetic. EPR results at low temperature indicate that the sample is paramagnetic, and that copper is placed in the tetragonal elongation (B) site with magnetically non-equivalent ions in the unit cell having strong exchange coupling between them. This property is useful in industrial applications. Nonlinear optical properties of the samples studied using 5 ns laser pulses at 532 nm employing the open aperture z-scan technique indicate that these ferrites are potential candidates for optical limiting applications.

Graphical abstract

Copper doped zinc aluminium ferrites are synthesized by the solid-state reaction route is cubic crystalline with unit cell parameter varying from 8.39 to 8.89 Å. TEM pictures clearly indicating that fundamental unit is composed of octahedral and tetrahedral blocks and joined strongly shown in (a). EPR spectra is compositional dependent at lower Al/Cu concentration EPR spectra is due to Fe3+ and at a higher content of Al/Cu the EPR spectra is due to Cu2+. Absence of EPR spectra at room temperature indicates that the sample is perfectly ferromagnetic. EPR results at low temperature indicate that the sample is paramagnetic, and that copper is placed in the tetragonal elongation (B) site with magnetically non-equivalent ions in the unit cell having strong exchange coupling between them. This is shown in (b). (a) TEM image of ferrite with x = 0.15. (b) EPR spectrum of ferrite with x = 0.75.

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Introduction

The spinel is a mixed metal oxide with a general formula (M2+)(M3+)2(O2)4 where M is a transition metal ion or a combination of ions. Many compounds adopt this type of structure. Generally magnetic ferrites are denoted by the formula AB2O4 where A and B refer to tetrahedral and octahedral sites respectively in the Fcc oxygen lattice. The unit cell contains eight formula units. Each unit cell consists of eight tetrahedral (A) sites and four octahedral (B) sites in the Fcc lattice. Hence half of the octahedral interstitial sites are occupied by trivalent metal ions and 1/8 of the tetrahedral interstitial sites are occupied by divalent ions in a normal spinel. In A site the divalent metal ion is in the center of a tetrahedron surrounded by four oxygens, whereas in B site the trivalent metal ion is in the center of an octahedron and is surrounded by six oxygens [1]. The equilibrium distribution of cations in the nanospinel compound structure depends on ionic radii, electronic configuration, chemical composition, method of preparation, grain size, electrostatic/crystal field stabilization energies (CFSE), and polarization effects [2], [3]. Cations like Zn2+, Mg2+ and Cd2+ show a strong preference for the A site, whereas Fe3+ ions prefer the B-sites. In inverse spinels cations like Mn2+, Ni2+, Co2+, Cu2+ occupy one of the B sites and hence one of the trivalent ion occupies tetrahedral sites thus inverting the structure. It is reported that the method of preparation plays a very important role with regard to the chemical, structural and magnetic properties of spinel ferrites [4].

In general spinels are classified into three types; viz. normal, inverse and mixed spinel. (Zn/Mg)Fe2O4 is a normal spinel, (Zn/Mg)(Al/Mn/CrNi/Fe)2O4 is a mixed spinel, and examples of inverse spinel include magnetite, NiFe2O4 etc., In all inverse spinels one of the trivalent ion is in tetrahedral hole and the divalent metal ion is in the octahedral hole. There are a total of 56 ions in the unit cell of a spinel, of which 8 are M2+ ions, 16 are M3+ ions and 32 are O2 ions. This is calculated as: 64 tetrahedral A site (8 × 8 = 64), 32 octahedral B site. Moreover, in normal spinel 8 M2+ are in the A site and 16 M3+ are in the B site, while in inverse spinel 8 M3+ are in the A site, and 8 M2+ and 8 M3+ are in the B site. In mixed spinels the cation distribution in the A and B sites is not exactly similar to that in the normal and inverse structures. The structural and the magnetic environments of these two sites are quite different from each other.

The substitution of nonmagnetic ions such as Al3+ ions in simple and mixed ferrites has received substantial attention over the past few years [5], [6], [7]. The introduction of paramagnetic copper is found to enhance the formation of mixed spinels. It has been reported that the presence of nonmagnetic ions reduces magnetic interactions between the two interstitial sites and weakens hyperfine magnetic fields, thereby changing the magnetic and electronic properties. In recent years, research on spinel ferrites has received renewed attention due to the availability of new and sophisticated techniques for the synthesis and characterization of nanoparticles. Normal ferrites are widely used for microwave and non-crystalline (powder) ferrites for high frequency applications but the nanoferrites have several uses in heat transfer devices, drug delivery systems, solar cell applications and medical diagnostics, including cancer treatment [8], [9]. It is well known that when ferrites are sufficiently diluted with non-magnetic atoms they can show a wide spectrum of magnetic structures, ferromagnetic order etc. [10]. From an application point of view, it is quite meaningful to investigate how the magnetic and electronic properties and the structure of mixed spinels change by the introduction of paramagnetic and non-magnetic atoms into the lattice. In fact to the best of our knowledge, EPR studies are not reported so far on ferrite systems which contain paramagnetic metal ions. Therefore, in the present work, we have synthesized copper doped zinc aluminum ferrites of nano-size via a solid-state route. XRD, EPR and TEM measurements have been carried out in order to determine the cation distribution in the ferrite system under study. Moreover, open aperture z-scan measurements have been done using 5 ns laser pulses at 532 nm to measure the nonlinear optical transmission of the samples, to calculate the nonlinear absorption coefficient, and estimate their potential for optical limiting applications.

Section snippets

Synthesis of nano-sized copper doped zinc aluminum ferrite

Samples of the mixed spinel ferrites (Zn1xCux)(AlxFe2x)O4 with variable composition (x = 0.15, 0.45, 0.75 and 0.90) are synthesized by using standard solid state route method. Mostly in the synthetic ferrite systems, Zn composition remains constant and is at its regular lattice site while Fe3+ was replaced by aluminum. But in the present syntheses composition of all Zn, Cu, Al and Fe ions are changed. All the chemicals used are of analytical grade only. Distilled water is used for the

X-ray diffraction results

Fig. 1 presents the X-ray diffraction patterns of all copper doped zinc aluminum ferrite samples recorded on Philips diffractometer up to 25°. In Fig. 1 all major peaks were indexed to the standard pattern for ferrite, Fe3O4. These peaks show the cubic spinel ferrite system. The values of the crystal lattice constant “a” for all the samples determined from X ray data are listed in Table 2. The lattice constant (a) is found to increase linearly with copper/aluminum concentration (x). This

Conclusions

  • 1.

    Ferrite compound is synthesized by standard solidstate route method shows crystallinity.

  • 2.

    XRD results suggest that a higher content of Cu result in the substitution of octahedral sites compared to tetrahedral sites. Further several crystal parameters are evaluated which are coinciding with TEM and SAED results.

  • 3.

    TEM images shows that the basic unit is composed of both tetrahedral and octahedral geometries and joined together to build the unit cell. TEM pictures are clearly shows both octahedral and

References (42)

  • N.R. Pawaskar et al.

    Mater. Res. Bull.

    (2002)
  • Q. Wang et al.

    Mater. Res. Bull.

    (2001)
  • H.C. Sampath Kumar et al.

    Chem. Phys. Lett.

    (2010)
  • B. Karthikeyan et al.

    Opt. Commun.

    (2008)
  • W.E. Ford

    A Text Book of Mineralogy

    (1989)
  • S. Son et al.

    J. Appl. Phys.

    (2002)
  • R.L. Dhiman, S.P. Taneja, V.R. Reddy, Advances in Condensed Matter Physics Volume 2008, Article ID 839536, 7 pages,...
  • J. Smith et al.

    Ferrites

    (1959)
  • Q.A. Pankhurst et al.

    Applications of magnetic nanoparticles in biomedicine

    J. Phys. D

    (2003)
  • R. Jurgons et al.

    Drug loaded magnetic nanoparticles for cancer therapy

    J. Phys.: Condens. Matter

    (2006)
  • J.L. Dormann et al.

    J. Phys.: Condens. Matter

    (1990)
  • Cited by (0)

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