Raman scattering spectra, magnetic and ferroelectric properties of BiFeO 3 –CoFe 2 O 4 nanocomposite thin films structure Mintu Tyagi a , Mukesh Kumari b , Ratnamala Chatterjee b , Puneet Sharma a,n a School of Physics & Materials Science, Thapar University, Patiala 147004, Punjab, India b Magnetics & Advanced Ceramics Laboratory, Department of Physics, Indian Institute of Technology, Delhi 110016, India article info Keywords: Ferrite films Composite films Sol–gel Raman spectroscopy Ferroelectric materials Magnetic properties abstract Multiferroic (1 x)BiFeO 3 (BFO)–xCoFe 2 O 4 (CFO) (x ¼0 and 0.1) nanocomposite thin films were deposited on ITO coated glass using sol–gel spin coating technique. X-ray diffraction and transmission electron microscopy examinations confirm the coexistence of both perovskite BFO and spinel CFO phases. The effect of addition of CFO in BFO matrix has been studied on Raman spectra, magnetic and ferroelectric properties. BFO/CFO nanocomposite showed good magnetic behavior (M s 40.3 emu/cm 3 , M r 12.9 emu/cm 3 , H c 90 Oe) with no change in ferroelectric properties. The strain analysis carried out by Raman spectroscopy reveals that both BFO and CFO bands are found to be strained in BFO/CFO composite nanostructure. The strain of the bands is discussed on the basis of lattice mismatch (interfacial stress) between CFO (a ¼0.839 nm) and BFO (a ¼0.396 nm) phases. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Multiferroic materials combining ferroelectric and magnetic order have gained considerable attention because of their potential applicability in spintronics, information storage and sensor tech- nologies [1–3]. Till date, several studies are reported on single and multiple phase multiferroic but very few of them have significant magnetoelectric (ME) coupling due to principle reasons [4]. Therefore, to overcome the scarcity of these multiferroics, the composite type artificial multiferroic materials or thin films nanos- tructures have generated particular interest because of their natu- rally stronger ME response [5–7]. BiFeO 3 (BFO) being a room temperature multiferroic (T C ¼ 1123 K and T N ¼ 643 K), has been widely studied [5,6]. It is known to exhibit excellent ferroelectric properties [8,9]. However, despite of this, the weak magnetic behavior of BFO limits its multifunctional applications [10]. To improve its magnetic properties, attempts have been made to develop composite nanostructures with spinel ferrites (AB 2 O 4 ). Recently, Sone et. al. reported an enhancement in magnetic behavior of BFO by distributing CoFe 2 O 4 (CFO) nanoparticles in its matrix [11]. In such systems, the elastic type interaction between the magnetostrictive CFO phase and the ferroelectric BFO phase leads to improve the magnetic properties as well as the magnetoelectric coupling between the two [12]. It has been reported by Zavaliche that elastic coupling between the two order parameters plays a major role in determining the magnetoelectric coupling of the nanocomposite structures [13]. Yan et al. has investigated the local probing of electromechanical coupling in BFO/CFO nanocomposite thin films [14]. Therefore, the study of lattice strain using the Raman scattering may reveal the strain mediation in BFO/CFO nanocomposite thin films. In this study, we have successfully realized a composite structure of BFO and CFO. The effects of CFO addition on structural, magnetic and ferroelectric properties of BFO/CFO nanocomposite films are investigated. The strain states of BFO and CFO in BFO/CFO nanocomposite films were studied using Raman scattering. 2. Experimental procedure The multiferroic BFO/CFO nanocomposite thin films were pre- pared by a sol–gel spin-coating technique. The solutions of BFO and CFO were prepared as discussed elsewhere [15]. Solution of both BFO and CFO were mixed in desired proportion and spin coated onto ITO coated glass substrate at 3000 rpm and subse- quently baked at 300 1C for 5 min. Finally, the thin films were obtained by repeating this spin-coating-baking process twice. The films were annealed at 600 1C for 20 min in ambient atmosphere. Phase analysis of the nanocomposite thin films was done by X-ray diffraction (XRD) using CuKα radiation (λ ¼ 1.54178 Ǻ) (Philips X-pert PRO). The microstructure of the BFO/CFO nanocomposite thin films was observed by plane view transmission electron microscopy (TEM TECNAI G2 20 S-TWIN). The standard ion beam milling procedure Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physb Physica B http://dx.doi.org/10.1016/j.physb.2014.03.014 0921-4526/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ91 9779533474; fax: 0175 2364498, 0175 2393005. E-mail address: puneet.sharma@thapar.edu (P. Sharma). Please cite this article as: M. Tyagi, et al., Physica B (2014), http://dx.doi.org/10.1016/j.physb.2014.03.014i Physica B ∎ (∎∎∎∎) ∎∎∎–∎∎∎