Multiferroic properties of a BiCrO3/BiFeO3 double-layered thin film prepared by chemical solution deposition

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Abstract

This study involved an investigation of the structural, electrical, and multiferroic properties of a BiCrO3/BiFeO3 (BCO/BFO) double-layered thin film that was prepared on a Pt(1 1 1)/Ti/SiO2/Si(1 0 0) substrate by using a chemical solution deposition method. X-ray diffraction and Raman spectroscopy studies revealed the formation of tetragonal and rhombohedral structures for the BCO/BFO double-layered thin film without any detectable secondary phases. A saturated ferroelectric hysteresis loop with a remnant polarization (2Pr) of 37 μC/cm2 and a coercive field (2Ec) of 1004 kV/cm at an applied electric field of 1154 kV/cm and a ferromagnetic hysteresis loop with a 2Mr value of 0.044 emu/cm2 and a 2Hc value of 276 Oe at a magnetic field of 10 kOe were observed for the BCO/BFO double-layered thin film at room temperature. The leakage current density of the BCO/BFO double-layered thin film was 2.88×10−4 A/cm2 at an external electric field of 100 kV/cm. The enhanced multiferroic properties observed for the BiCrO3/BiFeO3 thin film correlated with its net effects, such as a decrease in the oxygen vacancy density, a stabilization of the perovskite structure, and small changes in the lattice parameter caused by compressive strain resulting from the coupling of the BiFeO3 and BiCrO3 layers.

Introduction

A multiferroic material is described as a material that possesses two or more ferroic order parameters, such as ferroelectricity, ferromagnetism, and ferroelasticity in a single phase. The co-existence of strong ferroelectric and ferromagnetic properties in multiferroic materials is considered crucial for achieving magneto-electric coupling [1]. Multiferroic materials are expected to play an important role in the fabrication of magnetic sensors, data storage, spintronics, energy harvesting, and energy conversion devices [2], [3]. The existing classes of multiferroic systems are the RMnO3 (R=Dy, Tb, Ho, Y, Lu, for example), RMn2O5 (R=Nd, Sm, Dy, and Tb), and BiMO3 (M=Sc, Cr, Mn, Fe, Co, and Ni) families [4].

Among these, bismuth ferrite BiFeO3 (BFO) is the only known single-phase room-temperature multiferroic material with high ferroelectric (Tc~1103 K) and antiferromagnetic (TN~643 K) transition temperatures [5]. Although BFO exhibits excellent ferroelectric properties, its large leakage current density and weak magnetic properties limit its use in practical devices. Furthermore, the large leakage current of BFO leads to a decrease in the remnant polarization and an increase in the coercive electric field. Therefore, it is essential to control the leakage current to improve the multiferroic properties of BFO thin films. The factors that cause the large leakage current density in BFO are Bi deficiency, oxygen vacancies, valence fluctuation of the Fe (Fe2+/Fe3+) ion, and a poor microstructure [6], [7]. The weak magnetization of the BFO has been attributed to the cycloid spin structure. Recently, special attention has been paid to the combination of perovskite structures, such as BaTiO3 and Pb(Zr,Ti)O3, with BFO to form a double-layer thin film with the ultimate aim of obtaining potential multiferroic properties with a low leakage current density [8], [9].

BiCrO3 (BCO) is another ABO3-type perovskite multiferroic material with active lone pair electrons on the A-site and a magnetic transition metal (Cr) on the B-site, similar to BFO [10]. Thin films of BCO have been reported to exhibit ferroelectric properties at room temperature and antiferroelectric properties at 10 K, indicating the existence of a phase transition. However, similar to BFO, BCO thin films have been found to show poor magnetization [11]. According to a previous report the interaction between Fe3+ and Cr3+ plays a constructive role in the overall enhancement of the magnetization [12]. The above interaction would be more plausible if the BFO and the BCO were combined as a double-layered thin film. Furthermore, the highly resistive BCO should be able to act as a buffer layer. However, BCO is highly unstable; therefore, many efforts have been devoted to its synthesis using high-temperature and high-pressure techniques [13].

In this study, conditions were optimized for the formation of a BiCrO3/BiFeO3 (BCO/BFO) double-layered thin film with enhanced multiferroic properties and a low leakage current density. The BCO/BFO double-layered thin film was deposited on a Pt(1 1 1)/Ti/SiO2/Si(1 0 0) substrate by using a chemical solution deposition method to investigate the structural, electrical, and multiferroic properties and the results are discussed in detail.

Section snippets

Experimental procedure

The BiCrO3/BiFeO3 (BCO/BFO) double-layered thin film was prepared on a Pt(1 1 1)/Ti/SiO2/Si(1 0 0) substrate by using a chemical solution deposition method. Bismuth nitrate pentahydrate [Bi(NO3)3·5H2O], iron nitrate nonahydrate and chromium nitrate nonahydrate [Cr(NO3)3·9H2O] were used as raw materials. The solvent was prepared by mixing 2-methoxyethanol (CH3OCH2CH2OH) (2-MOE) and ethylene glycol (OHCH2CH2OH) (EG) at room temperature. Acetic acid was used as a catalyst. First, the acetic acid was

Results and discussion

Fig. 1 shows the X-ray diffraction (XRD) pattern of the BiCrO3/BiFeO3 (BCO/BFO) double-layered thin film deposited on a Pt(1 1 1)/Ti/SiO2/Si(1 0 0) substrate using a chemical solution deposition method. All peaks were indexed with reference to the distorted rhombohedral BFO [JCPDS no: 72-2035] and the tetragonal BCO [JCPDS no: 040570] phases. The BiCrO3 layer, generally known to be unstable as mentioned elsewhere in this paper, was stabilized by deposition on the BiFeO3 layer. The XRD pattern of

Conclusions

A BiCrO3/BiFeO3 (BCO/BFO) double-layered thin film was prepared on a Pt(1 1 1)/Ti/SiO2/Si(1 0 0) substrate by using a chemical solution deposition method, and its structural, electrical and multiferroic properties were investigated. The BCO/BFO double-layered thin film showed good multiferroic properties, such as well-saturated ferroelectric P-E hysteresis loops with 2Pr of 37 μC/cm2 and 2Ec of 1004 kV/cm at an applied electric field of 1154 kV/cm, well-saturated MH hysteresis loops with 2Mr of 0.044 

Acknowledgments

This work was supported by the Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0029634).

References (20)

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