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Effect of Annealing on Structural and Magnetic Properties of Magnetite Fe3O4 Thin Films Using Radio Frequency Magnetron Sputtering
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 2 (2015) 5601 – 5606
International Conference on Solid State Physics 2013 (ICSSP’13)
Effect of annealing on structural and magnetic properties of magnetite Fe3O4 thin films using radio frequency magnetron sputtering Haroon M. Jaral, Syed Sajjad Hussain*, Saira Riaz, Shahzad Naseema Centre of Excellence in Solid State Physics, University of the Punjab, Lahore-54590, Pakistan
Abstract
This research work discusses the effect of magnetic annealing time on the structural and magnetic properties of magnetite thin films. Thin films were made using Radio Frequency Magnetron Sputtering technique in Argon atmosphere. The samples were then annealed magnetically at constant temperature of 300 0C. The structural properties of Fe3O4 thin films were investigated using X-Ray Diffraction (XRD) while magnetic properties were studied using Vibrating Sample Magnetometer (VSM). The XRD results of these films confirmed the presence of the Fe 3O4. Experimental results indicated the change of alignment of all the atoms of thin film parallel to the direction of applied field. 2015Elsevier Elsevier Ltd. rights reserved. ©©2015 Ltd. AllAll rights reserved. Conference on Solid State Physics Selectionand and Peer-review under responsibility the Committee Members of International Selection Peer-review under responsibility of theofCommittee Members of International Conference on Solid State Physics 2013 2013(ICSSP’13) (ICSSP’13). Keywords: Magnetic annealing; Magnetic anisotropy, Magnetic properties, Soft magnetic materials, Magnetite thin films
* 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.2015.11.094
5602
Haroon M. Jaral et al. / Materials Today: Proceedings 2 (2015) 5601 – 5606
1. Introduction From past two decade, the study of magnetic properties of magnetite thin films has captivated many researchers. Due to its half-metallic response, it has so many applications in the field of spintronics [1]. Half metallicity refers to those mate-rials that response like metal in one spin orientation and insulator for other spin orientation at Fermi level. Band structure results have shown that Fe3O4 has 100% spin polarization [2]. Fe3O4 has higher Curie temperature (TC) of about 850 K. It is a mixed valence compound with ferric ions totally affiliated with the tetrahedral (A) sublattices, whereas half of the lattice sites are affiliated with Fe 2+ ions and other half by Fe3+ ions in octahedral (B) sublattices. Thus, magnetite indicates ferri-magnetic properties with A-site magnetic moment aligned anti-parallel to B-site magnetic moments below Cu-rie temperature [2]. Hence, due to its spectacular characteristics, it has numerous applications in tunnel magneto-resistance (TMR), giant magneto-resistance (GMR), physical optics, magnetic sensing technology, mass storage devices, high density magnetic recording devices, microwave devices [2], and in medical applications like magnetic resonance imaging (MRI), radio frequency hyperthermia, and medical diagnostic devices [3] 2. Experimental Before deposition, the glass substrate surface should be contamination free. We used Ultrasonic bathing method for surface cleaning. The substrates were first uncontaminated by isopropyl alcohol and acetone, and then placed in beaker for ultrasonic bathing which cleaned the surface of the substrate up to desired level. There are multiple techniques that are being used for deposit Fe 3O4 thin films on glass substrate e.g. reactive ion sputtering from iron target [4], plasma assisted molecular beam epitaxial growth [2,5], pulsed laser deposition from iron oxide target [4], sol-gel technique[6,7] and radio frequency magnetron sputtering from magnetite target [8,9] . Depending on deposition conditions, other oxides such as FeO and Fe2O3 have also been detected in as-deposited film. In this work, we deposited Fe3O4 thin film using radio frequency magnetron sputtering from Fe3O4 as target material. Thin films were fabricated directly on glass substrate with film thickness of the range of 50 nm. After deposition, the temperature of thin films was reduced to room temperature at rate of 10oC/min. Thin films were then annealed for 30 min, 60 min, and 90 min in magnetic annealing system at constant temperature of 300 oC in vacuum of about 10-2 torr. The films were then cooled very slowly to prevent cracking. The film thickness, structural and magnetic properties were analyzed by X-ray Diffraction (XRD) and Vibrating Sample Magnetometry (VSM). Table 1. Sputtering conditions of Fe3O4 thin films. Power (watt)
Argon inflow (sccm)
Base pressure (Pa)
Working pressure (Pa)
100
50
0.0019
0.425
3. Results and discussion Figure 1 is shows X-ray diffraction results of Fe3O4 thin film on glass substrate. The results indicated that the film was grown without any preferential direction. Thus XRD of as-deposited Fe3O4 thin films implied the amorphous structure of thin films. Figure 2 shows the XRD results of Fe3O4 thin film after magnetic annealing. It is observed that the thin film still do not have any sharp peak referring amorphous structure.
Haroon M. Jaral et al. / Materials Today: Proceedings 2 (2015) 5601 – 5606
5603
Fig. 1. XRD result of as deposited Fe3O4 thin film on glass substrate
Fig. 2. XRD results of Fe3O4 thin films after (a) 30 min, (b) 60 min, and (c) 90 min magnetic annealing at 300 oC each.
This is due to the reason that in the absence of applied field, a magnetically isotropic Fe3O4 thin film has no preferential alignment for its magnetic moment, but when external field is applied, Fe3O4 thin film arranged its moment with one of the easy axis. Thus it can be inferred that after magnetic annealing, the spins of every single atom aligned with the applied external field such that easy axis became aligned with the applied field. When temperature is reduced, the thin film again bolted and gained a new magnetization direction with well defined easy-axis.
5604
Haroon M. Jaral et al. / Materials Today: Proceedings 2 (2015) 5601 – 5606
Fig. 3. Room temperature M-H curves of Fe3O4 thin films annealed for 0, 30 and 60min.
5605
Haroon M. Jaral et al. / Materials Today: Proceedings 2 (2015) 5601 – 5606
Fig. 4. Room temperature hysteresis curve of Fe3O4 thin films annealed for 90min.
It is also observed from figure. 3 and figure.4 that before annealing, there were no strong magnetic moment seen in graph, but by increasing annealing time and then cooling down to room temperature, there formed a permanent uniaxial anisotropy along the easy axis parallel to the orientation of the applied field during annealing. Table 2. VSM results of Fe3O4 film annealed at different temperatures.
Annealing time (min)
Annealing temperature
Coercivity Hc
Retentivity
(G)
(K0)
(emu)
0-00
573.15
266.52
224.02x 10-6
0-30
573.15
1301.6
85.72x 10-6
0-60
573.15
379.26
211.48x 10-6
0-90
573.15
54.215
36.119x 10-6
From Table 2, it is inferred that the coercivity of the as-deposited thin film was 266.52G but for 30min it first increased to 1301.6G and then reduced to 54.215G for 90min annealed thin film. Thus coercivity is decreased after increasing annealing time. Hence thin films became magnetically softer along this easy axis than they were before annealing [10]. We have also seen that for 0-30min and 60min annealing time, the thin films were not fully saturated but after 90min annealing, the thin film were saturated completely. This indicates that magnetic annealing and annealing time plays a remarkable role in inducing the axial anisotropy in magnetite thin films.
5606
Haroon M. Jaral et al. / Materials Today: Proceedings 2 (2015) 5601 – 5606
4. Conclusions Fe3O4 thin films were deposited on glass substrate by radio frequency magnetron sputtering. Thin films were then annealed at constant temperature of 573.15 OK in the presence of external field in vacuum. XRD results implied the amorphous structure of thin films. VSM results declared that magnetic properties of Fe 3O4 thin films were increased after magnetic annealing. The saturation in the thin film happened after 90 min annealing. The coercivity and retentivity are decreased by increasing annealing time indicating Fe3O4; a soft magnetic material. References [1] S. Jain, A. O. Adeyeye, D. Y. Dai, Jr. Appl. Phys. 95, (2004) 11. [2] W.B Mi, J.J. Shen, E.Y. Jiang, H.L. Bai, 55 (2007) 1919. [3] W. Cai, J. Wan, Journal of Colloid and Interface Science 305 (2007) 366. [4] T. Furubayashi, J. Magn. Magn. Material 272-276 (2004) E781-E786. [5] D. Reisinger, P. Majewski, M. Opel, L. Alff,, R. Gross Appl. Phys. Lett. 85 (2004) 4980-4982. [6] W. Pan, J. Gong, L. Zhang, L. Che, Mater. Sci. Forum, 423-425 (2003) 569-572. [7] N. J. Tang, W. Zhong, W. Liu, H. Y. Jiang, X. L. Wu. Y. W. Du, J. Magn. Magn. Mater. 15 (2004) 1756. [8] B. Mauvernay, L. Presmanes, C. Bonningue, Ph. Tailhades, J. Magn. Magn. Mater. 320 (2008) 58-62. [9] M. Bohra, N. Venkataramani, S. Prasad, N. Kumar, D. S. Misra, S. C. Sahoo, Jr. R. Krishnan, Nanosci. Nanotechnol. 7, (2007) 2055-2057. [10] B.D. Cullity, Elements of X-Ray Diffraction, 1st edn. (Addison-Wesley, New York, 1956), pp. 110-111.
ScienceDirect Materials Today: Proceedings 2 (2015) 5601 – 5606
International Conference on Solid State Physics 2013 (ICSSP’13)
Effect of annealing on structural and magnetic properties of magnetite Fe3O4 thin films using radio frequency magnetron sputtering Haroon M. Jaral, Syed Sajjad Hussain*, Saira Riaz, Shahzad Naseema Centre of Excellence in Solid State Physics, University of the Punjab, Lahore-54590, Pakistan
Abstract
This research work discusses the effect of magnetic annealing time on the structural and magnetic properties of magnetite thin films. Thin films were made using Radio Frequency Magnetron Sputtering technique in Argon atmosphere. The samples were then annealed magnetically at constant temperature of 300 0C. The structural properties of Fe3O4 thin films were investigated using X-Ray Diffraction (XRD) while magnetic properties were studied using Vibrating Sample Magnetometer (VSM). The XRD results of these films confirmed the presence of the Fe 3O4. Experimental results indicated the change of alignment of all the atoms of thin film parallel to the direction of applied field. 2015Elsevier Elsevier Ltd. rights reserved. ©©2015 Ltd. AllAll rights reserved. Conference on Solid State Physics Selectionand and Peer-review under responsibility the Committee Members of International Selection Peer-review under responsibility of theofCommittee Members of International Conference on Solid State Physics 2013 2013(ICSSP’13) (ICSSP’13). Keywords: Magnetic annealing; Magnetic anisotropy, Magnetic properties, Soft magnetic materials, Magnetite thin films
* 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.2015.11.094
5602
Haroon M. Jaral et al. / Materials Today: Proceedings 2 (2015) 5601 – 5606
1. Introduction From past two decade, the study of magnetic properties of magnetite thin films has captivated many researchers. Due to its half-metallic response, it has so many applications in the field of spintronics [1]. Half metallicity refers to those mate-rials that response like metal in one spin orientation and insulator for other spin orientation at Fermi level. Band structure results have shown that Fe3O4 has 100% spin polarization [2]. Fe3O4 has higher Curie temperature (TC) of about 850 K. It is a mixed valence compound with ferric ions totally affiliated with the tetrahedral (A) sublattices, whereas half of the lattice sites are affiliated with Fe 2+ ions and other half by Fe3+ ions in octahedral (B) sublattices. Thus, magnetite indicates ferri-magnetic properties with A-site magnetic moment aligned anti-parallel to B-site magnetic moments below Cu-rie temperature [2]. Hence, due to its spectacular characteristics, it has numerous applications in tunnel magneto-resistance (TMR), giant magneto-resistance (GMR), physical optics, magnetic sensing technology, mass storage devices, high density magnetic recording devices, microwave devices [2], and in medical applications like magnetic resonance imaging (MRI), radio frequency hyperthermia, and medical diagnostic devices [3] 2. Experimental Before deposition, the glass substrate surface should be contamination free. We used Ultrasonic bathing method for surface cleaning. The substrates were first uncontaminated by isopropyl alcohol and acetone, and then placed in beaker for ultrasonic bathing which cleaned the surface of the substrate up to desired level. There are multiple techniques that are being used for deposit Fe 3O4 thin films on glass substrate e.g. reactive ion sputtering from iron target [4], plasma assisted molecular beam epitaxial growth [2,5], pulsed laser deposition from iron oxide target [4], sol-gel technique[6,7] and radio frequency magnetron sputtering from magnetite target [8,9] . Depending on deposition conditions, other oxides such as FeO and Fe2O3 have also been detected in as-deposited film. In this work, we deposited Fe3O4 thin film using radio frequency magnetron sputtering from Fe3O4 as target material. Thin films were fabricated directly on glass substrate with film thickness of the range of 50 nm. After deposition, the temperature of thin films was reduced to room temperature at rate of 10oC/min. Thin films were then annealed for 30 min, 60 min, and 90 min in magnetic annealing system at constant temperature of 300 oC in vacuum of about 10-2 torr. The films were then cooled very slowly to prevent cracking. The film thickness, structural and magnetic properties were analyzed by X-ray Diffraction (XRD) and Vibrating Sample Magnetometry (VSM). Table 1. Sputtering conditions of Fe3O4 thin films. Power (watt)
Argon inflow (sccm)
Base pressure (Pa)
Working pressure (Pa)
100
50
0.0019
0.425
3. Results and discussion Figure 1 is shows X-ray diffraction results of Fe3O4 thin film on glass substrate. The results indicated that the film was grown without any preferential direction. Thus XRD of as-deposited Fe3O4 thin films implied the amorphous structure of thin films. Figure 2 shows the XRD results of Fe3O4 thin film after magnetic annealing. It is observed that the thin film still do not have any sharp peak referring amorphous structure.
Haroon M. Jaral et al. / Materials Today: Proceedings 2 (2015) 5601 – 5606
5603
Fig. 1. XRD result of as deposited Fe3O4 thin film on glass substrate
Fig. 2. XRD results of Fe3O4 thin films after (a) 30 min, (b) 60 min, and (c) 90 min magnetic annealing at 300 oC each.
This is due to the reason that in the absence of applied field, a magnetically isotropic Fe3O4 thin film has no preferential alignment for its magnetic moment, but when external field is applied, Fe3O4 thin film arranged its moment with one of the easy axis. Thus it can be inferred that after magnetic annealing, the spins of every single atom aligned with the applied external field such that easy axis became aligned with the applied field. When temperature is reduced, the thin film again bolted and gained a new magnetization direction with well defined easy-axis.
5604
Haroon M. Jaral et al. / Materials Today: Proceedings 2 (2015) 5601 – 5606
Fig. 3. Room temperature M-H curves of Fe3O4 thin films annealed for 0, 30 and 60min.
5605
Haroon M. Jaral et al. / Materials Today: Proceedings 2 (2015) 5601 – 5606
Fig. 4. Room temperature hysteresis curve of Fe3O4 thin films annealed for 90min.
It is also observed from figure. 3 and figure.4 that before annealing, there were no strong magnetic moment seen in graph, but by increasing annealing time and then cooling down to room temperature, there formed a permanent uniaxial anisotropy along the easy axis parallel to the orientation of the applied field during annealing. Table 2. VSM results of Fe3O4 film annealed at different temperatures.
Annealing time (min)
Annealing temperature
Coercivity Hc
Retentivity
(G)
(K0)
(emu)
0-00
573.15
266.52
224.02x 10-6
0-30
573.15
1301.6
85.72x 10-6
0-60
573.15
379.26
211.48x 10-6
0-90
573.15
54.215
36.119x 10-6
From Table 2, it is inferred that the coercivity of the as-deposited thin film was 266.52G but for 30min it first increased to 1301.6G and then reduced to 54.215G for 90min annealed thin film. Thus coercivity is decreased after increasing annealing time. Hence thin films became magnetically softer along this easy axis than they were before annealing [10]. We have also seen that for 0-30min and 60min annealing time, the thin films were not fully saturated but after 90min annealing, the thin film were saturated completely. This indicates that magnetic annealing and annealing time plays a remarkable role in inducing the axial anisotropy in magnetite thin films.
5606
Haroon M. Jaral et al. / Materials Today: Proceedings 2 (2015) 5601 – 5606
4. Conclusions Fe3O4 thin films were deposited on glass substrate by radio frequency magnetron sputtering. Thin films were then annealed at constant temperature of 573.15 OK in the presence of external field in vacuum. XRD results implied the amorphous structure of thin films. VSM results declared that magnetic properties of Fe 3O4 thin films were increased after magnetic annealing. The saturation in the thin film happened after 90 min annealing. The coercivity and retentivity are decreased by increasing annealing time indicating Fe3O4; a soft magnetic material. References [1] S. Jain, A. O. Adeyeye, D. Y. Dai, Jr. Appl. Phys. 95, (2004) 11. [2] W.B Mi, J.J. Shen, E.Y. Jiang, H.L. Bai, 55 (2007) 1919. [3] W. Cai, J. Wan, Journal of Colloid and Interface Science 305 (2007) 366. [4] T. Furubayashi, J. Magn. Magn. Material 272-276 (2004) E781-E786. [5] D. Reisinger, P. Majewski, M. Opel, L. Alff,, R. Gross Appl. Phys. Lett. 85 (2004) 4980-4982. [6] W. Pan, J. Gong, L. Zhang, L. Che, Mater. Sci. Forum, 423-425 (2003) 569-572. [7] N. J. Tang, W. Zhong, W. Liu, H. Y. Jiang, X. L. Wu. Y. W. Du, J. Magn. Magn. Mater. 15 (2004) 1756. [8] B. Mauvernay, L. Presmanes, C. Bonningue, Ph. Tailhades, J. Magn. Magn. Mater. 320 (2008) 58-62. [9] M. Bohra, N. Venkataramani, S. Prasad, N. Kumar, D. S. Misra, S. C. Sahoo, Jr. R. Krishnan, Nanosci. Nanotechnol. 7, (2007) 2055-2057. [10] B.D. Cullity, Elements of X-Ray Diffraction, 1st edn. (Addison-Wesley, New York, 1956), pp. 110-111.