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Magnetic Properties of Sol-gel Deposited Magnetite Thin Films
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 2 (2015) 5395 – 5399
International Conference on Solid State Physics 2013 (ICSSP’13)
Magnetic properties of sol-gel deposited magnetite thin films Aseya Akbar*, Saira Riaz, Syed Sajjad Hussain and Shahzad Naseem Centre of Excellence in Solid State Physics, University of the Punjab, Lahore-54590, Pakistan
Abstract
Iron oxide has found wide applications in spintronic materials / devices. Iron oxide exists in three crystallographic phases namely magnetite, maghemite and hematite. Among these phases synthesis of magnetite phase is extremely difficult due to its complex oxidation kinetics. We here report preparation of magnetite thin films using sol-gel method. The concentration of sol is varied as 1.6mM, 1.2mM and 0.8mM. Pure magnetite phase is formed with sol concentration of 1.2mM. The films change their preferred orientation from (400) to (220) plane with phase transition from magnetite to maghemite. This phase transition from maghemite to maghemite is accompanied by an increase in saturation magnetization of the films. © 2015 2015Elsevier ElsevierLtd. Ltd. rights reserved. © AllAll rights reserved. Selectionand andPeer-review Peer-review under responsibility the Committee Members of International Conference on Solid State Physics Selection under responsibility of theofCommittee Members of International Conference on Solid State Physics 2013 2013(ICSSP’13) (ICSSP’13). Keywords: Thin films; Magnetic materials; Magnetite; Sol-gel
* Corresponding author. Tel.: +92-423-5839387. E-mail address: [email protected]
2214-7853 © 2015 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the Committee Members of International Conference on Solid State Physics 2013 (ICSSP’13) doi:10.1016/j.matpr.2015.11.057
5396
Aseya Akbar et al. / Materials Today: Proceedings 2 (2015) 5395 – 5399
1. Introduction Synthesis, progress and utilization of nanomaterials have become very broad and vigorously growing field of research in recent years. Out of the materials of interest in nano-regime iron oxide offers potential capability as building block for a very broad range of applications such as magnetic materials, chemical, electronic and biological sensors, data storage materials, MRI contrast agent and drug delivery facilitator [1-4]. Hence, synthesis of iron oxide on large scale with controlled particle size and morphology has become one of the most important research areas in the field of nanomaterial synthesis [5-10]. Magnetite (Fe3O4), hematite (Fe2O3) and Wustite (FeO) occur naturally while all other phases of iron oxide are formed artificially [1]. The oldest known iron oxide is hematite (α-Fe2O3) which is extensively found in rocks and salts. In finely divided form it is blood red in color and black or grey if roughly crystalline. It is also called ferric oxide, kidney ore, red ochre or martite [1]. It is the most thermally stable iron oxide present and is formed often by the transformation of other forms of iron oxide. The strongest magnetism is shown by magnetite (Fe3O4 or FeO.Fe2O3) which is also known as ferrous ferrite, black iron oxide, load stone. Maghemite occurs in soils as the result of weathering of magnetite or as the result of heating of other forms of iron oxide. It is the transition phase between magnetite (Fe3O4) and hematite (Fe2O3) [1, 11-13]. Fe3O4 has inverse spinel structure and γ-Fe2O3 has defect inverse spinel structure while α-Fe2O3 crystallizes in corundum structure [1-4]. Maghemite (γ-Fe2O3) and hematite (α-Fe2O3) contain only Fe2+ ions while Magnetite (Fe3O4) contains Fe2+ and Fe3+ ions. Fe3O4 and γ-Fe2O3 are ferrimagnetic while α-Fe2O3 is a weak ferromagnetic at room temperature [1]. Fe3O4 has certain advantages over other iron oxide phases. Fe3O4 is half metallic and has a high curie temperature as compared to other half metals. Moreover, Fe3O4 is a conductor at room temperature. Its conductivity is because of electron hopping between Fe2+ and Fe3+ cations present on the octahedral sites [1, 12-15]. Thin films of magnetite Fe3O4 are used in magnetic recording and data storage applications. For data storage devices the particles must have a switchable but stable magnetic state that must not be influenced by changes in temperature. In addition, for optimal performance in recording devices the particles must be uniform and possess high remanence and coercivity. Magnetite is also used in TMR (tunnelling magneto resistance) and room temperature GMR (giant magneto resistance) devices [1]. We here report the synthesis of magnetite thin films using sol-gel method. The concentration of sol was varied as 1.6mM, 1.2mM and 0.8mM. The sol concentration had a tremendous effect not only on the phase stability of iron oxide thin films but also affected the magnetic properties. 2. Experimental Details For preparation of iron oxide thin films iron chloride was dissolved in DI water. Another solution composed of NaOH and ethanol was added to the above solution. The solution was heated at 60˚C to obtain stable sol. Details of sol-gel synthesis have been reported earlier [9, 10]. The concentration of sol was varied as 1.6mM, 1.2mM and 0.8mM. The sols were spin coated on copper substrate. Before spin coating, substrates were etched using diluted HCl and then rinsed in deionized water. Substrates were then placed in ultrasonic bath in acetone and isopropyl alcohol for 10mins and 15mins respectively. Spin coating of sols on copper substrates was carried out using Delta 6RC spin coater. Films were dried at room temperature and were annealed in the presence of vacuum under the application of 500Oe magnetic field. The films were characterized structurally using Bruker D8 Advance X-ray Diffractometer. Magnetic properties were studied using Lakeshore’s 7407 Vibrating Sample Magnetometer. 3. Results and Discussion Fig. 1 shows XRD patterns of iron oxide thin films prepared using sol-gel method. Films are indexed according to JCPDS card no. 72-2303 and 39-1346 for magnetite and maghemite phases respectively. At sol concentration of 1.6mM presence of diffraction peaks corresponding to both magnetite and maghemite were present. It is
Aseya Akbar et al. / Materials Today: Proceedings 2 (2015) 5395 – 5399
5397
exceedingly complicated to differentiate magnetite from maghemite based on XRD pattern but comparison of JCPDS card no. 72-2303 and 39-1346 reveal that there are some diffraction peaks corresponding to maghemite that are not present in magnetite [9]. These diffraction peaks were observed in Fig 1(a) at 2θ˚=43.05˚ and 46.5˚. The presence of these diffraction peaks at sol concentration of 1.6mM (Fig. 1(a)) indicates mixed magnetite and maghemite phases. With decrease in sol concentration to 1.2mM formation of pure magnetite phase resulted as no peaks corresponding to maghemite can be observed in Fig. 1(b). Further decreasing the sol concentration to 0.8mM again resulted in formation of magnetite and maghemite mixed phases. As the only difference in magnetite and maghemite crystal structure is the presence of vacancies on cationic sublattice in maghemite so it can be predicted that both low and high concentration (1.6mM and 0.8mM) of sols results in creation of vacancies i.e. less conversion of Fe3+ to Fe2+ cations thus leading to presence of mixed phases [1].
Fig. 1. XRD pattern of iron oxide thin films with sol concentration (a) 1.6mM (b) 1.2mM (c) 0.8mM
Fig. 2. Room temperature M-H curves for iron oxide thin films
The films are oriented preferentially along (400) plane. Change in sol concentration to 1.2mM results in change in preferred orientation from (400) to (220) plane. This preferred orientation changes back to (400) as the sol concentration was decreased to 0.8mM. Crystallite size, dislocation density, strain, stacking fault probability and lattice parameters were calculated using Eqs. (1-5).
t=
0.9 λ B cos θ
(1)
δ=
1 t2
(2)
⎡ 2π 2 ⎤ ⎥ Δ 2θ SFP = ⎢ ⎢⎣ 45 3 tan θ ⎥⎦ Strain =
Δd d exp − d pdf = d d pdf
(3)
(4)
5398
Aseya Akbar et al. / Materials Today: Proceedings 2 (2015) 5395 – 5399
a2 =
λ2
⎛⎜ h 2 + k 2 + l 2 ⎞⎟ 2 ⎠ 4 sin θ ⎝
(5)
Where, λ is the wavelength taken as 1.5406Å, B is full width at half maximum, θ is the diffraction angle, (hkl) represent miller indices, d is the d-spacing. Calculated structural parameters of iron oxide thin films are listed in table 1. With increase in sol concentration as 0.8mM, 1.2mM and 1.6mM crystallite size increases as 18nm, 22nm and 28nm. As sol concentration is increased in case of sol-gel method number of colloidal particles increases. This increases the collision between the particles that causes increase in crystallite size with increase in sol concentration. Increased crystallite size with increased sol concentration resulted in decreased line dislocations in thin films along with reduced strain and stacking fault probability. In addition crystallite size in thin films is also strongly affected by neighboring grains as each grain in polycrystalline thin films have different energy due to curvature of energetic grain boundaries [14, 17-21]. Lattice parameter calculated using Eq. 5 is close to that of bulk magnetite. Table 1. Structural parameters for ron oxide thin films with sol concentration 0.8mM, 1.2mM, 1.6mM Strain Stacking Lattice Unit Sol Crystallite Dislocation paramet cell concentr size (nm) density (1015 (10-3) fault lines/m2) probabili er (Å) volume ation ty (Å3) 0.8mM 18 3.086 4.36 0.25 8.3568 583.60 1.2mM 22 2.066 3.26 0.21 8.3546 583.14 1.6mM 28 1.275 3.06 0.19 8.3543 583.08 Fig. 2 shows room temperature magnetization curves for films deposited using sol concentration of 1.6mM, 1.2mM and 0.8mM. Ferromagnetic behavior indicative of magnetite phase is observed for sol concentration of 1.2mM with high saturation magnetization. However, at sol concentration of 1.6mM and 0.8mM saturation magnetization is tremendously reduced. This reduction in saturation magnetization occurs due to two reasons (1) change of preferred orientation from (400) to (220) plane (2) phase transition from magnetite maghemite mixed phases to pure magnetite phase as was observed in Fig. 1(b). 4. Summary In summary: (1) Iron oxide thin films were prepared using sol-gel method with sol concentration of 1.6mM to 0.8mM. (2) Pure magnetite phase was formed with sol concentration of 1.2mM whereas 1.6mM and 0.8mM sol concentrations resulted in magnetite and maghemite mixed phases. (3) This phase transformation was accompanied by change in preferred orientation from (400) to (220) plane. (4) Highest saturation magnetization was observed for films with sol concentration of 1.2mM whereas the saturation magnetization decreased at sol concentration of 1.6mM and 0.8mM due to phase transition from magnetite to maghemite phase. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
D.J. Craik (ed.), Magnetic Oxides (John Wiley & Sons, New York, 1975) G. Schmidt, J. Phys. D: Appl. Phys. 38, R107 (2005) H. Yanagihara, M. Myoka, D. Isaka, T. Niizeki, K. Mibu, E. Kita, J. Phys. D: Appl. Phys. 46, 175004 (2013) M. F. Al-Kuhaili, M. Saleem, S. M. A. Durrani, J. Alloy. Compd. 521, 178 (2012) M. Monti, B. Santos, A. Mascaraque, O. R. Fuente, M. A. Nino, T. O. Mentes¸, A. Locatelli, K. F. McCarty, J. F. Marco, J. Figuera, Phys. Rev. B 85, 020404 (2012) O. Karaagac, H. Kockar, IEEE Trans. Magn. 48, 1532 (2012) O. Karaagac, H. Kockar, S. Beyaz, T. Tanrisever, IEEE. Tansc. Magn. 46, 3978 (2010) P. Kumar, R. K. Singh, N. Rawat, P. B. Barman, S. C. Katyal, H. Jang, H. N. Lee, R. Kumar, J. Nanopart. Res. 15, 1532 (2013) S. Riaz, A. Akbar, S. Naseem, Adv. Sci. Lett. 19, 828 (2013) S. Riaz, A. Akbar, S. Naseem, IEEE Trans. on Magn. 50, 2300204 (2014) W. Jiang, K. L. Lai, H. Hu, X. B. Zeng, F. Lan, K. X. Liu, Y. Wu, Z. W. Gu, J. Nanopart. Res. 13, 5135 (2011) X. J. Wu, Z. Z. Zhang, Q. S. Liang, J. Meng, J. Cryst. Growth 340, 74 (2012)
Aseya Akbar et al. / Materials Today: Proceedings 2 (2015) 5395 – 5399
[13] [14] [15] [16] [17] [18] [19] [20] [21]
X. Liu, H. Lu, M. He, L. Wang, H. Shi, K. Jin, C. Wang, G. Yang, J. Phys. D: Appl. Phys. 47, 105004 (2014) S. Riaz, S. Naseem, J. Mater. Sci. Technol. 23(4), 499 (2007) K. Joy, L. V. Maneeshya, J. K. Thomas, P. V. Thomas, Thin Solid Films 520, 2683 (2012) S. Riaz, M. Bashir, S. Naseem, IEEE Trans. Magn. 50, 4003304 (2014) S. Riaz, R. Ashraf, A. Akbar, S. Naseem, IEEE Trans. Magn. 50, 2201504 (2014) A. Akbar, S. Riaz, R. Ashraf, S. Naseem, IEEE Trans. Magn. 50, 2201204 (2014) S. Riaz, A. Akbar, S. Naseem, IEEE Trans. Magn. 50, 2200704 (2014) A. Akbar, S. Riaz, M. Bashir, S. Naseem, IEEE Trans. Magn. 50, 2200804 (2014) A. Akbar, S. Riaz, R. Ashraf, S. Naseem, J. Sol-Gel Sci. Technol., DOI 10.1007/s10971-014-3528-9 (2014)
5399
ScienceDirect Materials Today: Proceedings 2 (2015) 5395 – 5399
International Conference on Solid State Physics 2013 (ICSSP’13)
Magnetic properties of sol-gel deposited magnetite thin films Aseya Akbar*, Saira Riaz, Syed Sajjad Hussain and Shahzad Naseem Centre of Excellence in Solid State Physics, University of the Punjab, Lahore-54590, Pakistan
Abstract
Iron oxide has found wide applications in spintronic materials / devices. Iron oxide exists in three crystallographic phases namely magnetite, maghemite and hematite. Among these phases synthesis of magnetite phase is extremely difficult due to its complex oxidation kinetics. We here report preparation of magnetite thin films using sol-gel method. The concentration of sol is varied as 1.6mM, 1.2mM and 0.8mM. Pure magnetite phase is formed with sol concentration of 1.2mM. The films change their preferred orientation from (400) to (220) plane with phase transition from magnetite to maghemite. This phase transition from maghemite to maghemite is accompanied by an increase in saturation magnetization of the films. © 2015 2015Elsevier ElsevierLtd. Ltd. rights reserved. © AllAll rights reserved. Selectionand andPeer-review Peer-review under responsibility the Committee Members of International Conference on Solid State Physics Selection under responsibility of theofCommittee Members of International Conference on Solid State Physics 2013 2013(ICSSP’13) (ICSSP’13). Keywords: Thin films; Magnetic materials; Magnetite; Sol-gel
* Corresponding author. Tel.: +92-423-5839387. E-mail address: [email protected]
2214-7853 © 2015 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the Committee Members of International Conference on Solid State Physics 2013 (ICSSP’13) doi:10.1016/j.matpr.2015.11.057
5396
Aseya Akbar et al. / Materials Today: Proceedings 2 (2015) 5395 – 5399
1. Introduction Synthesis, progress and utilization of nanomaterials have become very broad and vigorously growing field of research in recent years. Out of the materials of interest in nano-regime iron oxide offers potential capability as building block for a very broad range of applications such as magnetic materials, chemical, electronic and biological sensors, data storage materials, MRI contrast agent and drug delivery facilitator [1-4]. Hence, synthesis of iron oxide on large scale with controlled particle size and morphology has become one of the most important research areas in the field of nanomaterial synthesis [5-10]. Magnetite (Fe3O4), hematite (Fe2O3) and Wustite (FeO) occur naturally while all other phases of iron oxide are formed artificially [1]. The oldest known iron oxide is hematite (α-Fe2O3) which is extensively found in rocks and salts. In finely divided form it is blood red in color and black or grey if roughly crystalline. It is also called ferric oxide, kidney ore, red ochre or martite [1]. It is the most thermally stable iron oxide present and is formed often by the transformation of other forms of iron oxide. The strongest magnetism is shown by magnetite (Fe3O4 or FeO.Fe2O3) which is also known as ferrous ferrite, black iron oxide, load stone. Maghemite occurs in soils as the result of weathering of magnetite or as the result of heating of other forms of iron oxide. It is the transition phase between magnetite (Fe3O4) and hematite (Fe2O3) [1, 11-13]. Fe3O4 has inverse spinel structure and γ-Fe2O3 has defect inverse spinel structure while α-Fe2O3 crystallizes in corundum structure [1-4]. Maghemite (γ-Fe2O3) and hematite (α-Fe2O3) contain only Fe2+ ions while Magnetite (Fe3O4) contains Fe2+ and Fe3+ ions. Fe3O4 and γ-Fe2O3 are ferrimagnetic while α-Fe2O3 is a weak ferromagnetic at room temperature [1]. Fe3O4 has certain advantages over other iron oxide phases. Fe3O4 is half metallic and has a high curie temperature as compared to other half metals. Moreover, Fe3O4 is a conductor at room temperature. Its conductivity is because of electron hopping between Fe2+ and Fe3+ cations present on the octahedral sites [1, 12-15]. Thin films of magnetite Fe3O4 are used in magnetic recording and data storage applications. For data storage devices the particles must have a switchable but stable magnetic state that must not be influenced by changes in temperature. In addition, for optimal performance in recording devices the particles must be uniform and possess high remanence and coercivity. Magnetite is also used in TMR (tunnelling magneto resistance) and room temperature GMR (giant magneto resistance) devices [1]. We here report the synthesis of magnetite thin films using sol-gel method. The concentration of sol was varied as 1.6mM, 1.2mM and 0.8mM. The sol concentration had a tremendous effect not only on the phase stability of iron oxide thin films but also affected the magnetic properties. 2. Experimental Details For preparation of iron oxide thin films iron chloride was dissolved in DI water. Another solution composed of NaOH and ethanol was added to the above solution. The solution was heated at 60˚C to obtain stable sol. Details of sol-gel synthesis have been reported earlier [9, 10]. The concentration of sol was varied as 1.6mM, 1.2mM and 0.8mM. The sols were spin coated on copper substrate. Before spin coating, substrates were etched using diluted HCl and then rinsed in deionized water. Substrates were then placed in ultrasonic bath in acetone and isopropyl alcohol for 10mins and 15mins respectively. Spin coating of sols on copper substrates was carried out using Delta 6RC spin coater. Films were dried at room temperature and were annealed in the presence of vacuum under the application of 500Oe magnetic field. The films were characterized structurally using Bruker D8 Advance X-ray Diffractometer. Magnetic properties were studied using Lakeshore’s 7407 Vibrating Sample Magnetometer. 3. Results and Discussion Fig. 1 shows XRD patterns of iron oxide thin films prepared using sol-gel method. Films are indexed according to JCPDS card no. 72-2303 and 39-1346 for magnetite and maghemite phases respectively. At sol concentration of 1.6mM presence of diffraction peaks corresponding to both magnetite and maghemite were present. It is
Aseya Akbar et al. / Materials Today: Proceedings 2 (2015) 5395 – 5399
5397
exceedingly complicated to differentiate magnetite from maghemite based on XRD pattern but comparison of JCPDS card no. 72-2303 and 39-1346 reveal that there are some diffraction peaks corresponding to maghemite that are not present in magnetite [9]. These diffraction peaks were observed in Fig 1(a) at 2θ˚=43.05˚ and 46.5˚. The presence of these diffraction peaks at sol concentration of 1.6mM (Fig. 1(a)) indicates mixed magnetite and maghemite phases. With decrease in sol concentration to 1.2mM formation of pure magnetite phase resulted as no peaks corresponding to maghemite can be observed in Fig. 1(b). Further decreasing the sol concentration to 0.8mM again resulted in formation of magnetite and maghemite mixed phases. As the only difference in magnetite and maghemite crystal structure is the presence of vacancies on cationic sublattice in maghemite so it can be predicted that both low and high concentration (1.6mM and 0.8mM) of sols results in creation of vacancies i.e. less conversion of Fe3+ to Fe2+ cations thus leading to presence of mixed phases [1].
Fig. 1. XRD pattern of iron oxide thin films with sol concentration (a) 1.6mM (b) 1.2mM (c) 0.8mM
Fig. 2. Room temperature M-H curves for iron oxide thin films
The films are oriented preferentially along (400) plane. Change in sol concentration to 1.2mM results in change in preferred orientation from (400) to (220) plane. This preferred orientation changes back to (400) as the sol concentration was decreased to 0.8mM. Crystallite size, dislocation density, strain, stacking fault probability and lattice parameters were calculated using Eqs. (1-5).
t=
0.9 λ B cos θ
(1)
δ=
1 t2
(2)
⎡ 2π 2 ⎤ ⎥ Δ 2θ SFP = ⎢ ⎢⎣ 45 3 tan θ ⎥⎦ Strain =
Δd d exp − d pdf = d d pdf
(3)
(4)
5398
Aseya Akbar et al. / Materials Today: Proceedings 2 (2015) 5395 – 5399
a2 =
λ2
⎛⎜ h 2 + k 2 + l 2 ⎞⎟ 2 ⎠ 4 sin θ ⎝
(5)
Where, λ is the wavelength taken as 1.5406Å, B is full width at half maximum, θ is the diffraction angle, (hkl) represent miller indices, d is the d-spacing. Calculated structural parameters of iron oxide thin films are listed in table 1. With increase in sol concentration as 0.8mM, 1.2mM and 1.6mM crystallite size increases as 18nm, 22nm and 28nm. As sol concentration is increased in case of sol-gel method number of colloidal particles increases. This increases the collision between the particles that causes increase in crystallite size with increase in sol concentration. Increased crystallite size with increased sol concentration resulted in decreased line dislocations in thin films along with reduced strain and stacking fault probability. In addition crystallite size in thin films is also strongly affected by neighboring grains as each grain in polycrystalline thin films have different energy due to curvature of energetic grain boundaries [14, 17-21]. Lattice parameter calculated using Eq. 5 is close to that of bulk magnetite. Table 1. Structural parameters for ron oxide thin films with sol concentration 0.8mM, 1.2mM, 1.6mM Strain Stacking Lattice Unit Sol Crystallite Dislocation paramet cell concentr size (nm) density (1015 (10-3) fault lines/m2) probabili er (Å) volume ation ty (Å3) 0.8mM 18 3.086 4.36 0.25 8.3568 583.60 1.2mM 22 2.066 3.26 0.21 8.3546 583.14 1.6mM 28 1.275 3.06 0.19 8.3543 583.08 Fig. 2 shows room temperature magnetization curves for films deposited using sol concentration of 1.6mM, 1.2mM and 0.8mM. Ferromagnetic behavior indicative of magnetite phase is observed for sol concentration of 1.2mM with high saturation magnetization. However, at sol concentration of 1.6mM and 0.8mM saturation magnetization is tremendously reduced. This reduction in saturation magnetization occurs due to two reasons (1) change of preferred orientation from (400) to (220) plane (2) phase transition from magnetite maghemite mixed phases to pure magnetite phase as was observed in Fig. 1(b). 4. Summary In summary: (1) Iron oxide thin films were prepared using sol-gel method with sol concentration of 1.6mM to 0.8mM. (2) Pure magnetite phase was formed with sol concentration of 1.2mM whereas 1.6mM and 0.8mM sol concentrations resulted in magnetite and maghemite mixed phases. (3) This phase transformation was accompanied by change in preferred orientation from (400) to (220) plane. (4) Highest saturation magnetization was observed for films with sol concentration of 1.2mM whereas the saturation magnetization decreased at sol concentration of 1.6mM and 0.8mM due to phase transition from magnetite to maghemite phase. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
D.J. Craik (ed.), Magnetic Oxides (John Wiley & Sons, New York, 1975) G. Schmidt, J. Phys. D: Appl. Phys. 38, R107 (2005) H. Yanagihara, M. Myoka, D. Isaka, T. Niizeki, K. Mibu, E. Kita, J. Phys. D: Appl. Phys. 46, 175004 (2013) M. F. Al-Kuhaili, M. Saleem, S. M. A. Durrani, J. Alloy. Compd. 521, 178 (2012) M. Monti, B. Santos, A. Mascaraque, O. R. Fuente, M. A. Nino, T. O. Mentes¸, A. Locatelli, K. F. McCarty, J. F. Marco, J. Figuera, Phys. Rev. B 85, 020404 (2012) O. Karaagac, H. Kockar, IEEE Trans. Magn. 48, 1532 (2012) O. Karaagac, H. Kockar, S. Beyaz, T. Tanrisever, IEEE. Tansc. Magn. 46, 3978 (2010) P. Kumar, R. K. Singh, N. Rawat, P. B. Barman, S. C. Katyal, H. Jang, H. N. Lee, R. Kumar, J. Nanopart. Res. 15, 1532 (2013) S. Riaz, A. Akbar, S. Naseem, Adv. Sci. Lett. 19, 828 (2013) S. Riaz, A. Akbar, S. Naseem, IEEE Trans. on Magn. 50, 2300204 (2014) W. Jiang, K. L. Lai, H. Hu, X. B. Zeng, F. Lan, K. X. Liu, Y. Wu, Z. W. Gu, J. Nanopart. Res. 13, 5135 (2011) X. J. Wu, Z. Z. Zhang, Q. S. Liang, J. Meng, J. Cryst. Growth 340, 74 (2012)
Aseya Akbar et al. / Materials Today: Proceedings 2 (2015) 5395 – 5399
[13] [14] [15] [16] [17] [18] [19] [20] [21]
X. Liu, H. Lu, M. He, L. Wang, H. Shi, K. Jin, C. Wang, G. Yang, J. Phys. D: Appl. Phys. 47, 105004 (2014) S. Riaz, S. Naseem, J. Mater. Sci. Technol. 23(4), 499 (2007) K. Joy, L. V. Maneeshya, J. K. Thomas, P. V. Thomas, Thin Solid Films 520, 2683 (2012) S. Riaz, M. Bashir, S. Naseem, IEEE Trans. Magn. 50, 4003304 (2014) S. Riaz, R. Ashraf, A. Akbar, S. Naseem, IEEE Trans. Magn. 50, 2201504 (2014) A. Akbar, S. Riaz, R. Ashraf, S. Naseem, IEEE Trans. Magn. 50, 2201204 (2014) S. Riaz, A. Akbar, S. Naseem, IEEE Trans. Magn. 50, 2200704 (2014) A. Akbar, S. Riaz, M. Bashir, S. Naseem, IEEE Trans. Magn. 50, 2200804 (2014) A. Akbar, S. Riaz, R. Ashraf, S. Naseem, J. Sol-Gel Sci. Technol., DOI 10.1007/s10971-014-3528-9 (2014)
5399