Sputter-prepared (001) BiFeO3 thin films with ferromagnetic L10-FePt(001) electrode on glass substrates
© Chang et al.; licensee Springer. 2012
Received: 9 May 2012
Accepted: 14 July 2012
Published: 3 August 2012
Highly textured BiFeO3(001) films were formed on L10-FePt(001) bottom electrodes on glass substrates by sputtering at reduced temperature of 400°C. Good electric polarization 2Pr = 80 and 95 μC/cm2, comparable to that of the reported epitaxial films, and coercivity Ec = 415 and 435 kV/cm are achieved in the samples with 20-nm- and 30-nm-thick electrodes. The BiFeO3(001) films show different degrees of compressive strain. The relation between the variations of strain and 2Pr suggests that the enhancement of 2Pr resulted from the strain-induced rotation of spontaneous polarization. The presented results open possibilities for the applications based on electric-magnetic interactions.
KeywordsMultiferroic BiFeO3 (001) films L10-FePt(001) underlayer Glass substrate
BiFeO3 (BFO) with a rhombohedral perovskite structure has attracted considerable attention due to its multiferroic properties above room temperature (RT) including high ferroelectric (TC = 830°C) and G-type antiferromagnetic (AFM) (TN = 370°C) transition temperatures[1–4]. Different from the spiral spin structure in bulk, BFO thin film exhibits an antiparallel AFM structure along , allowing coupling to the spins of a ferromagnetic (FM) layer at the interface. The coupling permits the possibilities of various advanced spintronic and memory devices based on the electric-magnetic interactions[2–5].
Ferroelectric properties of BFO films highly depend on preferred orientation[6–11]. (111)-textured BFO shows the highest remanent polarization 2Pr of approximately 200 μC/cm2[6–10]. Nevertheless, BFO(001) (2Pr = 40 to 120 μC/cm2) shows more advantages for practical uses, such as lower electrical coercive field (Ec), better fatigue resistance, and higher piezoelectric coefficient[9–12]. For the BFO films prepared by either pulsed laser deposition (PLD) or sputtering, the preferred orientation can be well controlled by either using proper single crystal substrates or controlling the texture of the perovskite electrode underlayers[2, 5–13].
However, the high processing temperature (Tp > 600°C)[6–10] as well as the cost of using perovskite substrates is not favorable to industry. Although it has been reported that the use of the metal electrode Pt can reduce Tp to about 500°C, single crystal substrates are still necessary for texture control of both Pt and BFO. Considering that the electric-magnetic coupling is the fundamental mechanism to function the related spintronic devices, development of FM electrode that can induce a specific texture of BFO is thus one of the most effective ways to facilitate this coupling.
However, no related investigation has been reported prior to the presented study. In this letter, we demonstrate the induction of the BFO(001) preferred orientation for the sputter-prepared thin films by strongly textured ferromagnetic electrode of L10(001) FePt on glass substrates. Structural as well as ferroelectric properties are reported in detail.
Results and discussion
The induction of strong (001) texture of BFO films using the ferromagnetic FePt(001) bottom electrode with thicknesses of 20 and 30 nm on glass substrates by rf sputtering is reported. A degree of preferred orientation (LOF = 0.79) higher than that of the film prepared by PLD on SrTiO3(001) is achieved in the sample with 30-nm-thick electrode at a reduced temperature of 400°C. 2Pr values of 80 and 95 μC/cm2 are obtained in the films with 20-nm- and 30-nm-thck electrodes, respectively, much higher than that of the BFO(001) epitaxial films with Pt(001) bottom electrode grown on single crystal substrates. The BFO(001) films with 20-nm- and 30-nm-thick electrodes exhibit different compressive strains of 0.19% and 0.84%, respectively, and the relation between the increments of 2Pr and biaxial strain suggests that the strain-induced polarization rotation mechanism reported previously is responsible for the variation of 2Pr. The results of this study demonstrate the advantages of fabricating BFO(001) films using ferromagnetic bottom electrode on non-textured substrates and open wide possibilities for advanced applications based on electric-magnetic couplings.
This research was supported by the National Science Council of Taiwan under grant nos. NSC-98-2112-M-029-001-MY3 and NSC-100-2112-M-029-002-MY3 and Tunghai Green Energy Development and Management Institute (TGEI).
- Teague JR, Gerson R, James WJ: Dielectric hysteresis in single crystal BiFeO3. Solid State Commun 1970, 8: 1073. 10.1016/0038-1098(70)90262-0View Article
- Wang J, Neaton JB, Zheng H, Nagarajan V, Ogale SB, Liu B, Viehland D, Vaithyanathan V, Schlom DG, Waghmare UV, Spaldin NA, Rabe KM, Wuttig M, Ramesh R: Epitaxial BiFeO3 multiferroic thin film heterostructures. Science 2003, 299: 1719. 10.1126/science.1080615View Article
- Catalan G, Scott JF: Physics and applications of bismuth ferrite. Adv Mater 2009, 21: 2463. 10.1002/adma.200802849View Article
- Bea H, Gajek M, Bibe M, Barthelemy A: Spintronics with multiferroics. J Phys Condens Matter 2008, 20: 434221. 10.1088/0953-8984/20/43/434221View Article
- Bea H, Bibes M, Fusil S, Bouzehouane K, Jacquet E, Rode K, Bencok P, Barthelemy A: Investigation on the origin of the magnetic moment of BiFeO3 thin films by advanced x- ray characterizations. Phys. Rev. B 2006, 74: 020101.View Article
- Li J, Wang J, Wuttig M, Ramesh R, Wang N, Ruette B, Pyatakov AP, Zvezdin AK, Viehland D: Dramatically enhanced polarization in (001), (101), and (111) BiFeO3 thin films due to epitiaxial-induced transitions. Appl Phys Lett 2004, 84: 5261. 10.1063/1.1764944View Article
- Das RR, Kim DM, Beak SH, Eom CB, Zavaliche F, Yang SY, Ramesh R, Chen YB, Pan XQ, Ke X, Rzchowski MS, Streiffer SK: Synthesis and ferroelectric properties of epitaxial BiFeO3 thin films grown by sputtering. Appl Phys Lett 2006, 88: 242904. 10.1063/1.2213347View Article
- Chu YH, Martin LW, Holcomb MB, Ramesh R: Controlling magnetism with multiferroics. Mater. Today 2007, 10: 16.View Article
- Jang HW, Beak SH, Ortiz D, Folkman CM, Eom CB, Chu YH, Shafer P, Ramesh R, Vaithyanathan V, Schlom DG: Epitaxial (001) BiFeO3 membranes with substantially reduced fatigue and leakage. Appl Phys Lett 2008, 92: 062910. 10.1063/1.2842418View Article
- Wu J, Wang J: Orientation dependence of ferroelectric behavior of BiFeO3 thin films. J Appl Phys 2009, 106: 104111. 10.1063/1.3261841View Article
- Ryu S, Son JY, Shih YH, Jang HM, Scott JF: Polarization switching characteristics of BiFeO3 thin films epitaxially grown on Pt/MgO at a low temperature. Appl Phys Lett 2009, 95: 242902. 10.1063/1.3275012View Article
- Wang J, Zheng H, Ma Z, Prasertchoung S, Wuttig M, Droopad R, Yu J, Eisenbeiser K, Ramesh R: Epitaxial BiFeO3 thin films on Si. Appl Phys Lett 2004, 85: 2574. 10.1063/1.1799234View Article
- Jang HW, Beak SH, Ortiz D, Folkman CM, Das RR, Chu YH, Shafer P, Zhang JX, Choudhury S, Vaithyanathan V, Chen YB, Felker DA, Biegalski MD, Rzchowski MS, Pan XQ, Schlom DG, Chen LQ, Ramesh R, Eom CB: Strain-induced polarization rotation in epitaxial (001) BiFeO3 thin films. Phys Rev Lett 2008, 101: 107602.View Article
- Villars P, Calvert LD: Pearson's Handbook of Crystallographic Data for Intermetallic Phase. Meta Park, OH: ASM; 2000.
- Hsiao N, Yuan FT, Chang HW, Huang HW, Chen SK, Lee HY: Effect of initial stress/strain state on order–disorder transformation of FePt thin films. Appl Phys Lett 2009, 94: 232505. 10.1063/1.3153513View Article
- Mei JK, Yuan FT, Liao WM, Sun AC, Yao YD, Lin HM, Hsu JH, Lee HY: Critical thickness of (001) texture induction in FePt thin films on glass substrates. IEEE Trans Magn 2011, 47: 3633.View Article
- Lotgering FK: Topotactical reactions with ferrimagnetic oxides having hexagonal crystal structures-I. J Inorg Nucl Chem 1959, 9: 113. 10.1016/0022-1902(59)80070-1View Article
- Bark CW, Cho KC, Koo YM, Tamura N, Ryu S, Jang HM: Two-dimensional mapping of triaxial strain fields in a multiferroic BiFeO3 thin film using scanning x-ray microdiffraction. Appl Phys Lett 2007, 90: 102904. 10.1063/1.2711530View Article
- Zheng RY, Gao XS, Zhou ZH, Wang J: Multiferroic BiFeO3 thin films deposited on SrRuO3 buffer layer by rf sputtering. J Appl Phys 2007, 101: 054104. 10.1063/1.2437163View Article
- Lee YH, Wu JM, Chueh YL, Chou LJ: Low-temperature growth and interface characterization of BiFeO3 thin films with reduced leakage current. Appl Phys Lett 2005, 87: 172901. 10.1063/1.2112181View Article
- Lee YH, Wu JM, Lai CH: Influence of La doping in multiferroic properties of BiFeO3 thin films. Appl Phys Lett 2006, 88: 042903. 10.1063/1.2167793View Article
- Ederer C, Spaldin NA: Effect of epitaxial strain on the spontaneous polarization of thin film ferroelectrics. Phys Rev Lett 2005, 95: 257601.View Article
- Zhang JX, Li YL, Wang Y, Liu ZK, Chen LQ, Chu YH, Zavaliche F, Ramesh R: Effect of substrate-induced strains on the spontaneous polarization of epitaxial BiFeO3 thin films. J Appl Phys 2007, 101: 114105. 10.1063/1.2743733View Article
- Fitzpatric ME, Lodini A (Eds): Analysis Of Residual Stress By Diffraction Using Neutron And Synchrotron Radiation. London: Taylor & Francis; 2003.
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.