- Email: [email protected]
Influence of transition elements doping on structural, optical and magnetic properties of BiFeO3 films fabricated by magnetron sputtering
Materials Letters 111 (2013) 123–125
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Influence of transition elements doping on structural, optical and magnetic properties of BiFeO3 films fabricated by magnetron sputtering Hurui Yan a, Hongmei Deng b, Nuofan Ding a, Jun He a, Lin Peng a, Lin Sun a, Pingxiong Yang a,n, Junhao Chu a a Key Laboratory of Polar Materials and Devices, Ministry of Education, Department of Electronics, East China Normal University, 500 Dongchuan Road, Shanghai 200241, China b Laboratory for Microstructures, Shanghai University, 99 Shangda Road, Shanghai 200444, China
art ic l e i nf o
a b s t r a c t
Article history: Received 13 May 2013 Accepted 18 August 2013 Available online 24 August 2013
Bi0.9La0.1Fe1 xCrxO3 (x ¼0.03, 0.05 and 0.07) thin films were deposited on LaNiO3/Si and quartz by RF magnetron sputtering, respectively. X-ray diffraction patterns indicate that all phases belong to BiFeO3, and no secondary phase is detected. Three A1 modes and six E modes of the films are observed in Raman scattering spectra, and the A1-1 peak position shows red shift with the increasing of x, which indicates that the Cr doping induces more structural distortion. The band gap of the films for x ¼0.03, 0.05 and 0.07 can be expressed by (2.99 x) eV, which is due to the Cr doping that increases the tailing of conduction band edge into the band gap. With the Cr content increasing from 3% to 7%, the remnant magnetization and the magnetization at 10 kOe of the films show about 202% and 55% addition, respectively. & 2013 Elsevier B.V. All rights reserved.
Keywords: BiFeO3 Ferroelectrics Thin films Optical properties Magnetic properties
1. Introduction Multiferroics is a kind of material which has the property of ferroelectric, ferromagnetism, ferroeleastic and ferrotoroidic simultaneously. Multiferroics has already attracted much attention due to its promising multifunctional device applications, such as magneto-electric sensor devices, memories spintronics [1,2]. As the only single-phase multiferroic material at room temperature, BiFeO3 (BFO) has high Curie temperature (TC 1103 K) and high Neel temperature (TN 643 K) [3,4]. BFO possesses spatially superimposed cycloid spin structure, which leads to no macroscopic magnetization and linear magneto-electric effect. Some groups have found the co-substitution of transition elements can suppress the spatially modulated spin structure, and have managed a way to enhance the magnetic properties of BFO [5,6]. The co-doping of La and Cr is also expected to improve the magnetic properties of BFO, and the effects of transition elements doping on the optical properties of BFO are also worth studying. In this paper, Bi0.9La0.1Fe1 xCrxO3 (xBLFCO, x¼0.03, 0.05 and 0.07) films were grown on LaNiO3 (LNO/Si) and quartz by RF magnetron sputtering, respectively. The microstructure, surface morphology, lattice vibrations modes, magnetic and optical properties were
n
Corresponding author. Tel.: þ 86 21 54345157; fax: þ86 21 54345119. E-mail address: [email protected] (P. Yang).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.08.075
analyzed. Especially, the optical properties of the xBLFCO films were first studied by transmittance spectra. 2. Experimental The xBLFCO (x¼ 0.03, 0.05 and 0.07) films were grown by RF magnetron sputtering. the xBLFCO (x¼0.03, 0.05 and 0.07) targets were synthesized by the solid-state reaction process, and high pure (99.99%) Bi2O3, La2O3, Fe2O3 and Cr2O3 were starting chemicals. Before the deposition of the xBLFCO films, 200 nm LNO buffer layer was deposited on Si substrate, then the xBLFCO films were deposited on LNO/Si. In order to study the optical properties, the xBLFCO films were also deposited on the quartz substrates. During the sputtering process, the Ar/O2 ratio was 5:1 and the power was controlled at 100 W. The crystal structures of the xBLFCO films grown on the LNO/Si and quartz substrate were identified by X-ray diffraction (XRD, D/MAX-2200, Rigaku Co.). The microstructure and surface morphologies of the xBLFCO/LNO/Si films were determined by scanning electron microscopy (SEM, Philips XL30FEG) and atomic force microscopy (AFM) (Digital Instruments Dimension 3100, Veeco), respectively. Raman scattering analysis of the films was carried out using micro-Raman spectrometer (Jobin-YvonLabRAM HR 800UV). The optical properties were characterized by transmittance spectra (PerkinElmer UV/VIS Lambda 2 S). The magnetic properties of the
124
H. Yan et al. / Materials Letters 111 (2013) 123–125
Fig. 1. (a) XRD patterns of the xBLFCO (x ¼0.03, 0.05 and 0.07) films deposited on quartz and LNO/Si substrates, respectively. (b) Surface and cross-section (inset) microscopy SEM image of 0.07BLFCO film on LNO/Si substrate. (c) AFM image with 5 μm 5 μm of 0.07BLFCO film on LNO/Si substrate.
samples were investigated by physical property measurement system (PPMS-9, Quantum Design).
3. Results and discussion Fig. 1(a) shows the XRD patterns of the xBLFCO (x ¼0.03, 0.05 and 0.07) films grown on LNO/Si and quartz substrates, respectively. The xBLFCO films have rhombohedral perovskite structure. The xBLFCO films on LNO/Si were dominantly oriented along the (101) direction, which is due to the LNO buffer layer [7]. The average crystallite sizes of the xBLFCO films on LNO/Si were estimated to be 45.0–55.2 nm using the Scherrer formula. In terms of the standard XRD patterns (PDF #14-0181), diffraction peaks (101), (110), (021), (202), (211) and (300) are found in the xBLFCO films deposited on quartz. No secondary phase is detected in the XRD patterns of films grown on both LNO/Si and quartz, which reveals that the La-modified BFO were optimized [8]. The peaks position shows insignificant shift, which means that the lattice parameters of the xBLFCO films are less affected by the doping of Cr3 þ ions, due to the similar radii of Cr3 þ and Fe3 þ ions [9]. The microstructure and surface morphologies of the xBLFCO (x ¼0.03, 0.05 and 0.07) films on LNO/Si were analyzed by SEM and AFM. Fig. 1(b–c) is a typical surface morphology and cross-section microscopy of SEM and the AFM image for 0.07BLFCO film on LNO/ Si substrate. As Fig. 1(b) shows, the film appears dense and crackfree in all scanned areas of the sample. The interface between the BLFCO film, LNO and substrate was very abrupt in cross-section microscopy, as shown in the inset of Fig. 1(b). The average thickness of the xBLFCO films are 360–390 nm from SEM images. The surface of 0.07BLFCO film on LNO/Si is uniform and dense as seen in the AFM image of Fig. 1(c). The root-mean-square roughness of the films is 4.8–5.8 nm determined by the AFM. Fig. 2 represents the Raman spectra of the xBLFCO films deposited on LNO/Si at room temperature. Through fitting the measured spectra and decomposing the fitted curves into individual Lorentzian components, we obtain the natural frequency of each Raman active mode in all samples. Group theory predict that there are 13(4A1 þ9E) Raman active modes being presented in the (R3c) BFO crystal [10]. Yuan et al. reported 9 Raman modes, containing three A1 modes at 152.6, 177.5 and 224.2 cm 1,
Fig. 2. Measured Raman scattering spectra (open circles), together with their fitted spectra (thick solid line) and the decomposed active modes (green solid lines) for the xBLFCO (x ¼0.03, 0.05 and 0.07) films grown on LNO/Si. The intensity of the 0.07BLFCO spectra has been amplified for better illustration; the inset shows the variation of A1-1 mode peak position.
six E modes at 270, 298.8, 354.9, 473.3, 554.3 and 618.3 cm 1 [11]. The active mode at 77 cm 1 (E-1 in Fig. 2) associates with Bi ions, whereas the mode at 136 cm 1 (A1-1 in Fig. 2) mode associates with Fe ions [12,13]. The inset of Fig. 2 shows the A1-1 peak position versus x. With the increase of Cr content, the A1-1 peak position shifts towards the lower wavenumber, revealing more structural distortion on Fe site happened. The red shift of A1-1 mode may be due to the Cr doping, as the mass of Cr3þ is smaller than Fe3þ . The xBLFCO films are direct band gap material, and the relationship of α constant and band gap energy (Eg) for the films can be described by Tauc representation [14,15]: αhνp (hν Eg)1/2, where α is the absorption coefficient and hν is photon energy. The (αhν)2 versus hν was plotted in Fig. 3. By extrapolating straight line, we can obtain the optical band gap. The determined Eg value of the xBLFCO films for x ¼0.03, 0.05 and 0.07 are 2.66, 2.64 and 2.61 eV. The results agree well with the reported values [16,17]. The band gap versus Cr content is plotted in the inset of Fig. 3, and the experimental values and fitting curves are displayed as dots and solid lines, respectively. With the increasing of Cr content, the band gap of the xBLFCO films decreases, which can be expressed
H. Yan et al. / Materials Letters 111 (2013) 123–125
125
4. Conclusions The xBLFCO films were successfully fabricated on LNO/Si and quartz substrates by RF magnetron sputtering, respectively. The XRD patterns show the lattice parameters are little affected by the increase of Cr content. SEM and AFM images show that the surface of the xBLFCO films is smooth. The A1-1 peak position of Raman spectra for the xBLFCO films shifts to lower wavenumber. The optical band gap of the xBLFCO (x ¼0.03, 0.05 and 0.07) films are 2.66, 2.64 and 2.61 eV, respectively, which may be expressed by Eg ¼(2.99 x) eV. The remnant magnetization of the films increases with Cr content, which indicates that the xBLFCO films have promising applications in data storage media. Fig. 3. (αE)2 plotted as function of photon energy for the xBLFCO (x ¼0.03, 0.05 and 0.07) thin films on quartz substrate. The inset shows the optical band gap of the xBLFCO (x¼ 0.03, 0.05 and 0.07) thin films versus Cr composition.
M (emu/cm3)
10
Acknowledgments This work was supported by the National Natural Science Foundation of China (60990312 and 61076060), Science and Technology Commission of Shanghai Municipality (10JC1404600).
xBLFCO
5 References
0
x=0.03 x=0.05 x=0.07
-5 -10 -10000
-5000
0
5000
10000
H (Oe) Fig. 4. M–H hysteresis loops of the xBLFCO (x¼ 0.03, 0.05 and 0.07) films on LNO/Si.
by Eg ¼(2.99 x) eV. The addition of Cr causes the absorption edge to shift toward lower photon energy, and to increase consequently tailing of conduction band edge into the band gap [18]. The magnetization hysteresis (M–H) loops of the xBLFCO films at room temperature are plotted in Fig. 4. Compared with Codoped BFO films [19,20], La/Cr co-doped BFO films exhibit larger magnetization at room temperature. It may be attributed to that La3 þ substituted to Bi3 þ which can suppress the spin spiral structure, then release weak ferromagnetism of BFO [11]. All films exhibit saturated magnetization with clear M–H hysteresis loops in Fig. 4. The saturation magnetization of the xBLFCO films increases with the addition of x from 0.03 to 0.07, and the remnant magnetization of the xBLFCO films are 1.75, 2.15 and 5.29 emu/ cm3 for x¼0.03, 0.05 and 0.07, respectively. The enhancement of magnetic properties is attributed to the increase of Cr content inducing more structure distortion and thus suppressing cycloid spin structure in the xBLFCO films [21,22], which is demonstrated by the Raman results.
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]
Eerenstein W, Mathur DD, Scott JF. Nature 2006;442:759–65. Catalan C, Scott JF. Advanced Materials 2009;21:2463–85. Kim JK, Su S, Kim KW. Mater Lett 2005;59:4006. Nalwa KS, Garg A, Upadhyaya A. Materials Letters 2008;62:878–81. Yang KG, Zhang YL, Yang SH, Wang B. Journal of Applied Physics 2010;107:124109. Jayakumar OD, Achary SN, Girija KG, Tyagi AK, Sudakar C. Applied Physics Letters 2010;96:032903. Huang DJ, Deng HM, Yang PX, Chu JH. Materials Letters 2010;64:2233–5. Singh SK, Maruyama K, Ishiwara H. Applied Physics Letters 2007;91:112913. Zhang YH, Yu SW, Cheng JR. Journal of the European Ceramic Society 2009;30:271–5. Fukumura H, Harima H, Kisoda K, Tamada M, Noguchi Y, Miyayama M. Journal of Magnetism and Magnetic Materials 2007;310:e367. Yuan GL, Or SW, Chan HLW. Journal of Applied Physics 2007;101:24106. Yasui S, Uchida H, Nakaki H, Nishida K. Applied Physics Letters 2007;91:022906. Kharel P, Talebi S, Ramachandran B, Dixit A. Journal of Physics: Condensed Matter 2009;21:036001. Tauc J, Grigorovici R, Vancu A. Physica Status Solidi 1966;15:627–37. Pankove JI. Optical Processes in Semiconductors. 2nd Ed. New Jersey: PrenticeHall; 1971. Luo BC, Chen CL, Jin KX, Zhou CC. Thin Solid Films 2011;519:3632–5. Ding NF, Deng HM, Yang PX, Chu JH. Materials Letters 2012;82:71–3. Qi XD, Dho J, Blamire M, Jia Q, Lee JS, Foltyn S, et al. Journal of Magnetism and Magnetic Materials 2004;283:415. Arya GS, Sharma RK, Negi NS. Materials Letters 2013;93:341–4. Yang CH, Sui HT, Jiang H, Xiong W, Xu HY. Materials Letters 2012;88:54–6. Bhushan B, Wang ZX, Tol JV, Dalal NS, Basumallick A, Vasanthacharya NY, et al. Journal of the American Ceramic Society 2012;95:1985. Wang N, Cheng J, Pyatokov A, Zvezdin AK, Li JF, Cross LE, et al. Physical Review B 2005;72:104434.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Influence of transition elements doping on structural, optical and magnetic properties of BiFeO3 films fabricated by magnetron sputtering Hurui Yan a, Hongmei Deng b, Nuofan Ding a, Jun He a, Lin Peng a, Lin Sun a, Pingxiong Yang a,n, Junhao Chu a a Key Laboratory of Polar Materials and Devices, Ministry of Education, Department of Electronics, East China Normal University, 500 Dongchuan Road, Shanghai 200241, China b Laboratory for Microstructures, Shanghai University, 99 Shangda Road, Shanghai 200444, China
art ic l e i nf o
a b s t r a c t
Article history: Received 13 May 2013 Accepted 18 August 2013 Available online 24 August 2013
Bi0.9La0.1Fe1 xCrxO3 (x ¼0.03, 0.05 and 0.07) thin films were deposited on LaNiO3/Si and quartz by RF magnetron sputtering, respectively. X-ray diffraction patterns indicate that all phases belong to BiFeO3, and no secondary phase is detected. Three A1 modes and six E modes of the films are observed in Raman scattering spectra, and the A1-1 peak position shows red shift with the increasing of x, which indicates that the Cr doping induces more structural distortion. The band gap of the films for x ¼0.03, 0.05 and 0.07 can be expressed by (2.99 x) eV, which is due to the Cr doping that increases the tailing of conduction band edge into the band gap. With the Cr content increasing from 3% to 7%, the remnant magnetization and the magnetization at 10 kOe of the films show about 202% and 55% addition, respectively. & 2013 Elsevier B.V. All rights reserved.
Keywords: BiFeO3 Ferroelectrics Thin films Optical properties Magnetic properties
1. Introduction Multiferroics is a kind of material which has the property of ferroelectric, ferromagnetism, ferroeleastic and ferrotoroidic simultaneously. Multiferroics has already attracted much attention due to its promising multifunctional device applications, such as magneto-electric sensor devices, memories spintronics [1,2]. As the only single-phase multiferroic material at room temperature, BiFeO3 (BFO) has high Curie temperature (TC 1103 K) and high Neel temperature (TN 643 K) [3,4]. BFO possesses spatially superimposed cycloid spin structure, which leads to no macroscopic magnetization and linear magneto-electric effect. Some groups have found the co-substitution of transition elements can suppress the spatially modulated spin structure, and have managed a way to enhance the magnetic properties of BFO [5,6]. The co-doping of La and Cr is also expected to improve the magnetic properties of BFO, and the effects of transition elements doping on the optical properties of BFO are also worth studying. In this paper, Bi0.9La0.1Fe1 xCrxO3 (xBLFCO, x¼0.03, 0.05 and 0.07) films were grown on LaNiO3 (LNO/Si) and quartz by RF magnetron sputtering, respectively. The microstructure, surface morphology, lattice vibrations modes, magnetic and optical properties were
n
Corresponding author. Tel.: þ 86 21 54345157; fax: þ86 21 54345119. E-mail address: [email protected] (P. Yang).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.08.075
analyzed. Especially, the optical properties of the xBLFCO films were first studied by transmittance spectra. 2. Experimental The xBLFCO (x¼ 0.03, 0.05 and 0.07) films were grown by RF magnetron sputtering. the xBLFCO (x¼0.03, 0.05 and 0.07) targets were synthesized by the solid-state reaction process, and high pure (99.99%) Bi2O3, La2O3, Fe2O3 and Cr2O3 were starting chemicals. Before the deposition of the xBLFCO films, 200 nm LNO buffer layer was deposited on Si substrate, then the xBLFCO films were deposited on LNO/Si. In order to study the optical properties, the xBLFCO films were also deposited on the quartz substrates. During the sputtering process, the Ar/O2 ratio was 5:1 and the power was controlled at 100 W. The crystal structures of the xBLFCO films grown on the LNO/Si and quartz substrate were identified by X-ray diffraction (XRD, D/MAX-2200, Rigaku Co.). The microstructure and surface morphologies of the xBLFCO/LNO/Si films were determined by scanning electron microscopy (SEM, Philips XL30FEG) and atomic force microscopy (AFM) (Digital Instruments Dimension 3100, Veeco), respectively. Raman scattering analysis of the films was carried out using micro-Raman spectrometer (Jobin-YvonLabRAM HR 800UV). The optical properties were characterized by transmittance spectra (PerkinElmer UV/VIS Lambda 2 S). The magnetic properties of the
124
H. Yan et al. / Materials Letters 111 (2013) 123–125
Fig. 1. (a) XRD patterns of the xBLFCO (x ¼0.03, 0.05 and 0.07) films deposited on quartz and LNO/Si substrates, respectively. (b) Surface and cross-section (inset) microscopy SEM image of 0.07BLFCO film on LNO/Si substrate. (c) AFM image with 5 μm 5 μm of 0.07BLFCO film on LNO/Si substrate.
samples were investigated by physical property measurement system (PPMS-9, Quantum Design).
3. Results and discussion Fig. 1(a) shows the XRD patterns of the xBLFCO (x ¼0.03, 0.05 and 0.07) films grown on LNO/Si and quartz substrates, respectively. The xBLFCO films have rhombohedral perovskite structure. The xBLFCO films on LNO/Si were dominantly oriented along the (101) direction, which is due to the LNO buffer layer [7]. The average crystallite sizes of the xBLFCO films on LNO/Si were estimated to be 45.0–55.2 nm using the Scherrer formula. In terms of the standard XRD patterns (PDF #14-0181), diffraction peaks (101), (110), (021), (202), (211) and (300) are found in the xBLFCO films deposited on quartz. No secondary phase is detected in the XRD patterns of films grown on both LNO/Si and quartz, which reveals that the La-modified BFO were optimized [8]. The peaks position shows insignificant shift, which means that the lattice parameters of the xBLFCO films are less affected by the doping of Cr3 þ ions, due to the similar radii of Cr3 þ and Fe3 þ ions [9]. The microstructure and surface morphologies of the xBLFCO (x ¼0.03, 0.05 and 0.07) films on LNO/Si were analyzed by SEM and AFM. Fig. 1(b–c) is a typical surface morphology and cross-section microscopy of SEM and the AFM image for 0.07BLFCO film on LNO/ Si substrate. As Fig. 1(b) shows, the film appears dense and crackfree in all scanned areas of the sample. The interface between the BLFCO film, LNO and substrate was very abrupt in cross-section microscopy, as shown in the inset of Fig. 1(b). The average thickness of the xBLFCO films are 360–390 nm from SEM images. The surface of 0.07BLFCO film on LNO/Si is uniform and dense as seen in the AFM image of Fig. 1(c). The root-mean-square roughness of the films is 4.8–5.8 nm determined by the AFM. Fig. 2 represents the Raman spectra of the xBLFCO films deposited on LNO/Si at room temperature. Through fitting the measured spectra and decomposing the fitted curves into individual Lorentzian components, we obtain the natural frequency of each Raman active mode in all samples. Group theory predict that there are 13(4A1 þ9E) Raman active modes being presented in the (R3c) BFO crystal [10]. Yuan et al. reported 9 Raman modes, containing three A1 modes at 152.6, 177.5 and 224.2 cm 1,
Fig. 2. Measured Raman scattering spectra (open circles), together with their fitted spectra (thick solid line) and the decomposed active modes (green solid lines) for the xBLFCO (x ¼0.03, 0.05 and 0.07) films grown on LNO/Si. The intensity of the 0.07BLFCO spectra has been amplified for better illustration; the inset shows the variation of A1-1 mode peak position.
six E modes at 270, 298.8, 354.9, 473.3, 554.3 and 618.3 cm 1 [11]. The active mode at 77 cm 1 (E-1 in Fig. 2) associates with Bi ions, whereas the mode at 136 cm 1 (A1-1 in Fig. 2) mode associates with Fe ions [12,13]. The inset of Fig. 2 shows the A1-1 peak position versus x. With the increase of Cr content, the A1-1 peak position shifts towards the lower wavenumber, revealing more structural distortion on Fe site happened. The red shift of A1-1 mode may be due to the Cr doping, as the mass of Cr3þ is smaller than Fe3þ . The xBLFCO films are direct band gap material, and the relationship of α constant and band gap energy (Eg) for the films can be described by Tauc representation [14,15]: αhνp (hν Eg)1/2, where α is the absorption coefficient and hν is photon energy. The (αhν)2 versus hν was plotted in Fig. 3. By extrapolating straight line, we can obtain the optical band gap. The determined Eg value of the xBLFCO films for x ¼0.03, 0.05 and 0.07 are 2.66, 2.64 and 2.61 eV. The results agree well with the reported values [16,17]. The band gap versus Cr content is plotted in the inset of Fig. 3, and the experimental values and fitting curves are displayed as dots and solid lines, respectively. With the increasing of Cr content, the band gap of the xBLFCO films decreases, which can be expressed
H. Yan et al. / Materials Letters 111 (2013) 123–125
125
4. Conclusions The xBLFCO films were successfully fabricated on LNO/Si and quartz substrates by RF magnetron sputtering, respectively. The XRD patterns show the lattice parameters are little affected by the increase of Cr content. SEM and AFM images show that the surface of the xBLFCO films is smooth. The A1-1 peak position of Raman spectra for the xBLFCO films shifts to lower wavenumber. The optical band gap of the xBLFCO (x ¼0.03, 0.05 and 0.07) films are 2.66, 2.64 and 2.61 eV, respectively, which may be expressed by Eg ¼(2.99 x) eV. The remnant magnetization of the films increases with Cr content, which indicates that the xBLFCO films have promising applications in data storage media. Fig. 3. (αE)2 plotted as function of photon energy for the xBLFCO (x ¼0.03, 0.05 and 0.07) thin films on quartz substrate. The inset shows the optical band gap of the xBLFCO (x¼ 0.03, 0.05 and 0.07) thin films versus Cr composition.
M (emu/cm3)
10
Acknowledgments This work was supported by the National Natural Science Foundation of China (60990312 and 61076060), Science and Technology Commission of Shanghai Municipality (10JC1404600).
xBLFCO
5 References
0
x=0.03 x=0.05 x=0.07
-5 -10 -10000
-5000
0
5000
10000
H (Oe) Fig. 4. M–H hysteresis loops of the xBLFCO (x¼ 0.03, 0.05 and 0.07) films on LNO/Si.
by Eg ¼(2.99 x) eV. The addition of Cr causes the absorption edge to shift toward lower photon energy, and to increase consequently tailing of conduction band edge into the band gap [18]. The magnetization hysteresis (M–H) loops of the xBLFCO films at room temperature are plotted in Fig. 4. Compared with Codoped BFO films [19,20], La/Cr co-doped BFO films exhibit larger magnetization at room temperature. It may be attributed to that La3 þ substituted to Bi3 þ which can suppress the spin spiral structure, then release weak ferromagnetism of BFO [11]. All films exhibit saturated magnetization with clear M–H hysteresis loops in Fig. 4. The saturation magnetization of the xBLFCO films increases with the addition of x from 0.03 to 0.07, and the remnant magnetization of the xBLFCO films are 1.75, 2.15 and 5.29 emu/ cm3 for x¼0.03, 0.05 and 0.07, respectively. The enhancement of magnetic properties is attributed to the increase of Cr content inducing more structure distortion and thus suppressing cycloid spin structure in the xBLFCO films [21,22], which is demonstrated by the Raman results.
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]
Eerenstein W, Mathur DD, Scott JF. Nature 2006;442:759–65. Catalan C, Scott JF. Advanced Materials 2009;21:2463–85. Kim JK, Su S, Kim KW. Mater Lett 2005;59:4006. Nalwa KS, Garg A, Upadhyaya A. Materials Letters 2008;62:878–81. Yang KG, Zhang YL, Yang SH, Wang B. Journal of Applied Physics 2010;107:124109. Jayakumar OD, Achary SN, Girija KG, Tyagi AK, Sudakar C. Applied Physics Letters 2010;96:032903. Huang DJ, Deng HM, Yang PX, Chu JH. Materials Letters 2010;64:2233–5. Singh SK, Maruyama K, Ishiwara H. Applied Physics Letters 2007;91:112913. Zhang YH, Yu SW, Cheng JR. Journal of the European Ceramic Society 2009;30:271–5. Fukumura H, Harima H, Kisoda K, Tamada M, Noguchi Y, Miyayama M. Journal of Magnetism and Magnetic Materials 2007;310:e367. Yuan GL, Or SW, Chan HLW. Journal of Applied Physics 2007;101:24106. Yasui S, Uchida H, Nakaki H, Nishida K. Applied Physics Letters 2007;91:022906. Kharel P, Talebi S, Ramachandran B, Dixit A. Journal of Physics: Condensed Matter 2009;21:036001. Tauc J, Grigorovici R, Vancu A. Physica Status Solidi 1966;15:627–37. Pankove JI. Optical Processes in Semiconductors. 2nd Ed. New Jersey: PrenticeHall; 1971. Luo BC, Chen CL, Jin KX, Zhou CC. Thin Solid Films 2011;519:3632–5. Ding NF, Deng HM, Yang PX, Chu JH. Materials Letters 2012;82:71–3. Qi XD, Dho J, Blamire M, Jia Q, Lee JS, Foltyn S, et al. Journal of Magnetism and Magnetic Materials 2004;283:415. Arya GS, Sharma RK, Negi NS. Materials Letters 2013;93:341–4. Yang CH, Sui HT, Jiang H, Xiong W, Xu HY. Materials Letters 2012;88:54–6. Bhushan B, Wang ZX, Tol JV, Dalal NS, Basumallick A, Vasanthacharya NY, et al. Journal of the American Ceramic Society 2012;95:1985. Wang N, Cheng J, Pyatokov A, Zvezdin AK, Li JF, Cross LE, et al. Physical Review B 2005;72:104434.