The study of the electric and magnetic properties of PbZr0.2Ti0.8O3–BiFeO3 multilayers

doi:10.1016/j.tsf.2011.03.136

Thin Solid Films

Volume 519, Issue 19, 29 July 2011, Pages 6269-6277

https://doi.org/10.1016/j.tsf.2011.03.136 Get rights and content

Abstract

The results of the electric and magnetic measurements performed on PbZr_0.2Ti_0.8O₃–BiFeO₃ symmetric structures, deposited on Pt/Si wafers, were compared for different number of layers in order to analyse the effect of interfaces over the macroscopic properties. It was found that the shape and magnitude of the capacitance–voltage characteristic, as well as the shape and parameters of the ferroelectric and magnetic hysteresis, depend on the number of interfaces in the intended multilayer structure. A temperature induced gradual transition from a magnetically disordered spin glass like phase of low temperature to an uncompensated antiferromagnetic phase at room temperature takes place in the BiFeO₃ films, under low applied magnetic fields. A partial ferromagnetic like order can be obtained at low temperatures by increasing the field. The observed changes in the electric and magnetic behaviour of the systems were related to an increased degree of disorder for electric dipoles and magnetic moments, due to the increased number of layers and crystallization treatments.

Introduction

The interest to study oxide multilayers and superlattices made from materials with different characteristics had increased very much in the last decade due to the fact that the super-structure may present new or enhanced properties, valuable for the design of the next generation of memory devices [1]. The presence of the interfaces can change the expected physical properties due to strain and charge effects [2]. Especially the combination of different ferroelectric, ferromagnetic and/or multiferroic materials is very attractive, being possible to obtain “artificial multiferroics” or ferroelectrics with intriguing properties (antiferroelectricity, enhanced dielectric constant, etc.) [3], [4], [5], [6]. One very interesting property of natural or “artificial” multiferroics is the presence of the magneto-electric effect, consisting in the ability to generate a voltage by applying a magnetic field, and vice-versa. In other words, it should be possible to control the ferroelectric polarization with a magnetic field and the magnetization with an electric field [3]. Another interesting phenomenon is the magnetocapacitive effect, offering the possibility to control the capacitance with a magnetic field [7]. Of increased interest are those materials and structures for which the capacitance can be controlled by both electric and magnetic fields. Such properties, which are very valuable for applications in the field of information storage or microwave telecommunications, can be offered by either a mixtures of ferroelectric and ferromagnetic materials [8], [9] or single composition multiferroic materials like for example BiFeO₃ [10], [11].

“Artificial multiferroics” may be obtained also by combining ferroelectrics with single composition multiferroics. Among ferroelectrics, lead zirconate–titanate (Pb(Zr,Ti)O₃, shortly PZT) offers a unique set of ferroelectric–electric properties, making it very useful for the electronic and optoelectronic industry [12], [13], [14]. As mentioned above, bismuth ferrite BiFeO₃ (BFO) is a single composition multiferroic with useful applications in the emerging field of spintronics [3]. It has a high transition temperature for the ferroelectric phase (Curie temperature T_C ~ 1100 K), as well as for the G-type antiferromagnetic phase (Neel temperature T_N ~ 650 K) [15]. The theoretical calculations show that BFO should have high polarization value, possibly higher than 100 μC/cm². Experimental results show that, indeed, the ferroelectric polarization in single crystal BFO is around 100 μC/cm² [16]. This value is comparable with that reported for epitaxial, tetragonal Pb(Zr_1 − xTi_x)O₃ films [17].

The combination of the two materials in multilayer thin films offer the possibility to obtain structures with new and superior properties compared to the component materials. Several methods have been developed to prepare epitaxial and polycrystalline films of PZT or BFO type, such as pulsed laser deposition, chemical solution deposition and magnetron sputtering [18], [19], [20]. Among these methods, the sol–gel method [13], [21], [22], is very popular because it provides good reproducibility, low cost and uniform thickness.

The electric and magnetic properties of BiFeO₃–PbZr_0.2Ti_0.8O₃ multilayers were investigated in this paper, in relation with the number of interfaces. All the samples were deposited by sol–gel on Pt/TiO₂/SiO₂/Si wafers (Pt/Si). The effect of multiple interfaces on the ferroelectric and magnetic hysteresis is analyzed and explained in terms of increased disorder in the dipole or spin networks. On the other hand, interfaces induce an additive contribution to the measured capacitance, leading to an apparent increase of the dielectric constant.

Section snippets

Experimental methods

The synthesis of 0.5 M PZT sol with a Zr/Ti ratio of 20/80 starts from alcoxide precursors: lead acetate Pb(CH₃COO)₂·3H₂O (Reactivul Bucuresti), zirconium n-propoxide Zr[O(CH₂)₂CH₃]₄ and titanium isopropoxide Ti[OCH(CH₃)₂]₄ (Alfa) dissolved in solvent 2-methoxyethanol (Aldrich). The conditions for the deposition of the PZT film are presented in previous publications [23], [24]. The stock solution of 0.3 M BFO was prepared starting from bismuth nitrate [Bi(NO₃)₃·5H₂O] (Fluka) and iron nitrate

Structure

The XRD diffraction patterns for the three multilayer structures are shown in Fig. 1, together with the pattern for a single composition BFO film. In all cases the diffraction peaks correspond to perovskite structures of BFO and PZT (the characteristic peaks of rhombohedral BFO and tetragonal PZT structures). The single BFO phase was indexed after JCPDS 01-086-1518. The presence of some parasitic phases can be observed in this case (e. g. Bi₂₅FeO₃₉, possible Fe₂O₃). In the case of multilayer

Conclusions

PZT-BFO-PZT multilayers have been prepared by sol–gel method on platinized silicon wafer. The properties of multilayers were studied function of number of interfaces and compared, when necessary, with the properties of single composition BFO films. The electric measurements had revealed and AFE-like behavior of multilayers, although the component materials are both FE. A monotonic increase of capacitance with the number of interfaces was observed, while the tunability is reduced by increasing

Acknowledgements

The work was financed through the PNCDI2 contracts No. 72 149-HETOX and No. 71 032-VALS (Romanian Ministry of Education and Research), and FP7 project IFOX (grant agreement no. 246102).

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The study of the electric and magnetic properties of PbZr0.2Ti0.8O3–BiFeO3 multilayers

Abstract

Introduction

Section snippets

Experimental methods

Structure

Conclusions

Acknowledgements

J. Eur Ceram. Soc.

Mater. Sci. Eng. B

Thin Solid Films

Nat. Mater.

Annu. Rev. Mater. Res.

Nature

Nat. Mater.

New J. Phys.

Appl. Phys. Lett.

Appl. Phys. Lett.

Science

Thin Solid Films

Appl. Phys. Lett.

Appl. Surf. Sci.

Ferroelectric Memories

Thin Solid Films

Phys. Rev. B

Adv. Mater.

Appl. Phys. Lett.

J. Korean Phys. Soc.

Appl. Phys. Lett.

Appl. Phys.

Appl. Phys. Lett.

J. Optoel. Adv. Mat.

J. Optoel. Adv. Mat.

J. Appl. Phys.

Appl. Phys. Lett.

The study of the electric and magnetic properties of PbZr_0.2Ti_0.8O₃–BiFeO₃ multilayers