Elsevier

Materials Letters

Volume 79, 15 July 2012, Pages 65-68
Materials Letters

Giant magnetocapacitance effect in nickel zinc ferrite impregnated mesoporous silica

https://doi.org/10.1016/j.matlet.2012.03.076Get rights and content

Abstract

Mesoporous silica with a pore diameter of around 5 nm was synthesized by a solution technique. Nickel zinc ferrite (NZF) phase was grown within these nanochannels. The dielectric permittivity showed dispersion as a function of frequency characteristic of a Maxwell–Wagner capacitor. The nanocomposite exhibited a large magneto-capacitance coefficient of 44% at room temperature at an applied magnetic field of 1.5 T. The dielectric loss of the nanocomposite was fairly low (~ 0.01). The present strategy of composite synthesis will lead to the preparation of materials having large values of magneto-capacitive coefficients for device applications.

Highlights

► Synthesis of nickel zinc ferrite supported mesoporous silica nanocomposite (NC). ► The NC exhibits a magneto-capacitance coefficient of 44% at room temperature. ► The dielectric loss of the nanocomposites was fairly low (~0.01).

Introduction

Multiferroic materials constitute an important area of research because of a wide variety of application possibilities e.g., multiple state memory systems, magnetic field sensors, signal processing devices [1], 2, [3]. The interest on these materials essentially grew out of their unique property of possessing both ferroelectric and ferromagnetic order as well as the associated magneto-electric coupling [4], [5], [6]. Single phase multiferroic materials being few in nature have low values of magneto-electric coupling coefficient [7], [8]. A number of nanocomposites were synthesized comprising ferroelectric and ferromagnetic phases with nanodimensions of different morphologies [9], [10], [11] e.g., multilayers or laminates, core–shell, nanopillars or nanoparticles in a matrix. Recently it was predicted by theoretical analysis that a large magneto-dielectric effect can be achieved in a heterogeneous sample system assuming the presence of magnetoresistance in one of the phases [12], [13]. The effect was shown to owe its origin to Maxwell–Wagner space charge polarization at the interfaces of two phases having widely different values of electrical conductivities. Recently the study of silica based ordered mesoporous materials achieved a great interest due to its potential application in many fields like as absorbents, catalysts, optically active materials, humidity and gas sensor technologies and some other field [14], [15], [16], [17], [18], [19] due to their high surface area, tunable pore size, large pore volume and stable mesoporous structure. Due to its unique property ordered mesoporous silica has potential applications in biomedicine as a drug delivery system [20]. Our approach has been to prepare a composite of nanoferrite and a porous insulator. A large value of magnetocapacitive coefficient was achieved. The effect was due to a giant magnetoresistance change in the ferrite phase. The details are reported in this paper.

Section snippets

Experimental

We have synthesized mesoporous silica template KIT-6 according to a method reported earlier [21] having pore size of the order of 5 nm and impregnated these by Ni0.5Zn0.5Fe2O4 through a solution route with a view to generating magneto-dielectric response by the above mentioned mechanism. In this procedure KIT-6 powder was immersed into ethanolic solution of nitrate salts and was stirred for a day. The KIT-6 was collected through filtration and washed with ethanol and distilled water. After

Results and discussions

Fig. 1(a) shows the transmission electron micrograph of the KIT-6 mesoporous silica template. The pore channels can be seen to have diameters around 5 nm. In Fig. 1(b) the microstructure of the composite is given which shows some of the channels filled up by nickel zinc ferrite. This is confirmed by the electron diffraction obtained from Fig. 1(b) and shown in Fig. 1(c). The interplanar spacings were calculated from Fig. 1(c). These values are found to be in satisfactory agreement with the JCPDS

Conclusions

In summary, NZF phase was grown within the nanochannels of mesoporous silica having a channel diameter of around 5 nm. The dielectric permittivity (real and imaginary parts) showed dispersion as a function of frequency which is characteristic of a Maxwell–Wagner capacitor. The nanocomposite exhibited a large magneto-capacitance coefficient viz., 44% at room temperature for an applied magnetic field of 1.5 T. Though nickel zinc ferrite is supposed to be a bad insulator the sparsely distributed

Acknowledgment

The work was carried out under an Indo-Australian project supported by DST, New Delhi. SB thanks CSIR, New Delhi for awarding a senior research fellowship. The help of Dhriti Ranjan Saha in carrying out some calculations is gratefully acknowledged. DC thanks INSA, New Delhi for giving him an honorary scientist's position.

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