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Structure, magnetic and electrical properties of soft magnetic Co–C amorphous thin films
Physics Letters A 316 (2003) 122–125 www.elsevier.com/locate/pla
Structure, magnetic and electrical properties of soft magnetic Co–C amorphous thin films Hao Wang a,b,∗ , M.F. Chiah c , W.Y. Cheung c , S.P. Wong c a Key Laboratory for Thin Film and Microfabrication of Ministry of Education, Research Institute of Micro/Nanometer Science and
Technology, Shanghai Jiao Tong University, Shanghai 200030, PR China b Faculty of Physics and Electronic Technology, Hubei University, Wuhan 430062, PR China c Department of Electronic Engineering and Materials Science and Technology Research Center, The Chinese University of Hong Kong,
Shatin, N.T., Hong Kong, PR China Received 25 March 2003; accepted 10 July 2003 Communicated by J. Flouquet
Abstract Amorphous Cox C1−x thin films, with x in the range of 60–75% in atomic percentage, have been prepared by pulsed filtered vacuum arc deposition. The structures of the films were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The in-plane magnetic hysteresis loops were measured by a superconducting quantum interference device magnetometer at room temperature. The electrical transport properties were measured by the four-probe technique at various temperatures ranging from 20 to 300 K. The films were found to be magnetically soft with coercivities in the range of 2 to 12 Oe, resistivities in the range of 130 to 300 µ cm, and magnetic saturation flux densities in the range of 6 to 13 kG. The films also showed good thermal stability in their structural, electrical and magnetic properties upon annealing up to 200 ◦ C in a vacuum furnace. 2003 Elsevier B.V. All rights reserved. PACS: 75.50.Kj; 75.70.-i; 75.50.Ss Keywords: Magnetic properties; Resistivity; Microstructure; Co–C films; Magnetic recording
With the increase of magnetic recording area density, high coercivity media and high data rates are needed. As a consequence, it brings challenges to write head performance to write high coercivity media at high frequencies. The general requirements for thin film head core material are high saturation flux density (Bs ) to generate high field without saturation
* Corresponding author.
E-mail address: [email protected] (H. Wang). 0375-9601/$ – see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0375-9601(03)01135-6
of the core, low coercivity (Hc ) to reduce magnetic hysteresis loss, reasonable high permeability (µ) to be used at high frequency, high resistivity (ρ) to suppress eddy currents, high anisotropy (Hk ) to eliminate ferromagnetic resonance loss, zero magnetostriction (λs ) to ensure the magnetic field not producing stress in the film, high Curie temperature (Tc ) to sustain thermal stability, and good corrosion resistance to survive fabrication and file requirements. So far, the core material for commercial write head is electroplated permalloy developed by IBM in 1991
H. Wang et al. / Physics Letters A 316 (2003) 122–125
[1]. However, the moderate Bs (9–10 kG) and low ρ (20–25 µ cm) may limit its applications in the case of ultra high-density recording. The traditionally only choice of high frequency bulk core material is ferrite for its high ρ value, but it is not suitable for magnetic integrated circuit and thin film head applications due to the low Bs , low initial µ, and low Tc [2]. FeXN (X = Al, Zr, Ta, V, Ti, W, Hf) films have very high Bs (∼20 kG) and poses great potential as write head core materials for ultra high-density magnetic recording applications [3–6]. However, these films have been known to have problems at high frequencies due to the moderate ρ (∼100 µ cm). The very high Bs (20–21 kG) and near zero λs properties of Co rich CoFe and CoNiFe alloys make them promising materials for future write head core applications [7–9]. However, they are also metallic and sensitive to corrosion, which significantly lower their competitiveness for high frequency applications. Another attractive candidate developed more recently is the nanogranular or nanocomposite thin films, such as Fe–Al–O, Co–SiO2 , Co–Al–O, Co–Zr–O, Co–MF2 , CoFe–O, and CoFe–B–O [2,10–13]. These films consist of high moment transition metal or alloy nanograins encapsulated in an insulating matrix, which can have very high ρ in the range of 102 – 108 µ cm (depending on composition), good for GHz data rates applications. However, there are also problems with the nanogranular films. For examples, there is inherent trade-off between high ρ and low Hc and that between high ρ and high Bs . In this Letter, we shall report the structural, magnetic and electrical properties of Co–C granular films prepared by pulsed filtered vacuum arc deposition. Thin Cox C1−x (x = 60–75 at%) films of 20–27 nm thickness were prepared by a 3-source pulsed filtered vacuum arc deposition system, of which the details have been described elsewhere [14,15]. Two adjacent sources with pure graphite and cobalt as the cathode materials were operated simultaneously in a pulsed mode with a pulse duration of 2.5 ms. The substrate was placed at the center of the chamber facing to the bisector of the two sources and a negative bias voltage of −80 V was applied. The composition of the Co–C films was varied by adjusting the arc discharge conditions and was monitored by the integrated charges arriving at the sample holder from the respective arc sources. The as-deposited films were an-
123
Fig. 1. TEM plan-view bright field (BF) micrographs and electron diffraction (ED) pattern (insert) for the as-deposited Co65 C35 film.
nealed in a vacuum furnace (∼8 × 10−4 Pa) at various temperatures ranging from 200 to 400 ◦ C for 1 h to see the thermal annealing effects on the structural and magnetic properties. The composition of the films was determined by non-Rutherford backscattering spectrometry (NRBS). The microstructures of the films were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and Xray photoelectron spectroscopy (XPS). The magnetic properties were measured by a SQUID magnetometer. The resistivity was measured by the conventional fourprobe technique. Carbon coated Cu grids and Si (100) wafers with 50 nm thermally grown SiO2 on top were used as the substrates. Samples on copper grids were used for TEM studies, and those on Si substrates were used for the other measurements. Both TEM and XRD results showed that the asdeposited Cox C1−x films were amorphous even the carbon concentration was as high as 75% in atomic ratio. Fig. 1 is the plan-view bright field (BF) micrographs and electron diffraction (ED) pattern (insert) for the as-deposited Co65 C35 film. As shown in Fig. 1, the ED pattern shows halos, indicating that the film is amorphous. The BF micrograph shows granular structure though the contrast is weak. Judging from the micrograph, the typical granule size is about 3–4 nm. As reported in our previous papers [16,17], upon thermal annealing to a temperature (dependent on composition) between about 250 to 350 ◦ C, the as-deposited amorphous films went through a metastable stage at which a cobalt carbide phase and the
124
H. Wang et al. / Physics Letters A 316 (2003) 122–125
Fig. 2. XRD patterns for the Co70 C30 films, as-deposited and annealed at 300 and 400 ◦ C.
hexagonal close-packed (hcp) crystalline cobalt phase co-existed according to the TEM ED patterns. Upon further annealing to a sufficiently higher temperature (dependent on composition) between about 350 to 400 ◦ C, the carbide phase decomposed into hcp crystalline cobalt grains and graphite-like carbon. Such a change in crystalline phase against thermal treatment for these Co–C systems was also verified by XRD experiments. Typically, Fig. 2 is the X-ray diffraction pattern for the Co70 C30 film. The as-deposited sample shows a broadened peak centered at about 44◦ , indicating an amorphous-like structure. Also shown in Fig. 2 are the XRD patterns for the annealed samples. After annealing at 300 ◦ C, small diffraction peaks originating from hcp Co and δ –Co2 C appear, showing the co-existence of nanocrystals for the two phases in the film. Upon further increase of annealing temperature to 400 ◦ C, only those diffraction peaks belonging to hcp Co are observed due to the complete decomposition of the metastable carbide phase. On the other hand, XPS is helpful for the understanding of the phase transition of Cox C1−x films against thermal annealing. While the binding energies of the Co–2p peak in pure cobalt and cobalt carbides almost coincide with each other, those of the C–1s peak in cobalt carbide and amorphous carbon or graphite are different. Fig. 3 shows the C–1s spectra for the Co75 C25 film, as-deposited and annealed at various temperatures. The spectra were deconvoluted into two Gaussian peaks centered at about 283.1 and 284.5 eV, respectively. The peak at 283.1 eV corre-
Fig. 3. C–1s spectrum for the Co75 C25 film, the as-deposited and annealed at 300 and 400 ◦ C. The solid lines are experimental data and the dash lines are fitting results.
sponds to the binding energy of C–1s in cobalt carbide, and the peak at 284.5 eV corresponds to that of carbon–carbon bonds. As shown in Fig. 3, both carbide bonds and C–C bonds exist in the samples, asdeposited and annealed at 300 ◦ C. For the sample annealed at 400 ◦ C, the C–1s spectrum basically consists of only one peak at about 284.5 eV corresponding to C–C bonds, indicating the complete decomposition of the carbide phase. The in-plane magnetic hysteresis loops for the Cox C1−x films show that the as-deposited amorphous films are magnetically soft. The round shape hysteresis loops with squareness (remaneance ratio) smaller than 0.28 were observed in the films with Co content smaller than 65 at%. On the other hand, rectangular hysteresis loops with squareness in the range of 0.98 to 1 were obtained in the films with Co content larger than 70 at% [16]. Fig. 4 is the saturation flux density and coercivity as functions of Co concentration for the amorphous Cox C1−x films. With increasing Co concentration, while Bs increases almost linearly, Hc increases only slightly. The highest Bs value of 13 kG was achieved in the Co75 C25 film due to the largest amount of Co content. The slight increase of Hc with Co concentration maybe caused by the weak nanocrystallization of the Co grains leading to an enhancement of magnetocrystalline anisotropy.
H. Wang et al. / Physics Letters A 316 (2003) 122–125
125
In summary, we have prepared Cox C1−x (x = 60– 75 at%) thin films by pulsed filtered vacuum arc deposition. The as-deposited films are amorphous and magnetically soft. For a Co75 C25 film, the saturation flux density is 13 kG, the coercivity is 12 Oe, and the room temperature resistivity is 130 µ cm. The films are thermally stable upon vacuum annealing up to 200 ◦ C. These newly reported films may seek their applications as high-density magnetic recording head. Acknowledgements Fig. 4. The Bs and Hc as functions of Co concentration for the amorphous Cox C1−x films.
This work is supported in part by the Research Grants Council of Hong Kong SAR (Ref. No. CUHK4216/00E) and the China Education Ministry (Ref. No. 2001345). References
Fig. 5. The Co concentration dependence of resistivity for the as-deposited Cox C1−x films.
The temperature dependence of the resistivity for the amorphous Cox C1−x films showed metallic properties. The room-temperature resistivity is in the range of 130–300 µ cm, which is larger than those of magnetically soft alloys and FeN films. Fig. 5 shows the Co concentration dependence of room-temperature resistivity for these films. The resistivity increases with decreasing Co content. The ρ value is larger than 1000 µ cm when the Co content is smaller than about 35 at%. The microstructure results suggested that the high resistivity in the film is related to the partial surface oxidation of Co grains as inferred from the XPS results and the high resistivity of the amorphous carbon prepared by filtered vacuum arc deposition [14,18]. The as-deposited amorphous Cox C1−x films also showed good thermal stabilities in their structural, magnetic and electrical properties upon vacuum annealing up to 200 ◦ C.
[1] C. Tsang, M.M. Chen, T. Yogi, K. Ju, IEEE Trans. Magn. 26 (1990) 1689. [2] H. Fujimori, Scripta Metallurgica Materialia 33 (1995) 1625. [3] W.P. Jayasedara, S. Wang, M.H. Kryder, J. Appl. Phys. 79 (1996) 5880. [4] Y.K. Liu, M.H. Kryder, Appl. Phys. Lett. 77 (2000) 426. [5] V.R. Inturi, J.A. Barnard, J. Appl. Phys. 81 (1997) 4504. [6] L. Vrga, H. Jiang, T.J. Klemmer, W.D. Doyle, E.A. Payzant, J. Appl. Phys. 83 (1998) 5955. [7] C.L. Platt, A.E. Berkowitz, D.J. Smith, M.R. McCartney, J. Appl. Phys. 88 (2000) 2058. [8] T. Osaka, M. Takai, K. Hayashi, K. Ohashi, M. Saito, K. Yamada, Nature 392 (1998) 796. [9] X. Liu, P. Evans, G. Zangari, IEEE Trans. Magn. 36 (2000) 3479. [10] S. Ohnuma, H.J. Lee, N. Kobayashi, H. Fujimori, T. Masumoto, IEEE Trans. Magn. 37 (2001) 2251. [11] K.S. Kim, K.S. Byon, S.C. Yu, S.R. Kim, S.H. Han, Scripta Mater. 44 (2001) 1447. [12] Y.D. Zhang, S.H. Wang, D.T. Xiao, J.I. Budnick, W.A. Hines, IEEE Trans. Magn. 37 (2001) 2275. [13] G.S.D. Beach, A.E. Berkowitz, F.T. Parker, D.J. Smith, Appl. Phys. Lett. 79 (2001) 224. [14] S.P. Wong, H. Wang, N. Ke, W.Y. Cheung, M.F. Chiaf, D.H. Chen, Q.J. Li, H. Liu, X.X. Zhang, Int. J. Mod. Phys. B 14 (2000) 321. [15] H. Wang, S.P. Wong, W.Y. Cheung, N. Ke, W.F. Lau, M.F. Chiah, X.X. Zhang, Mater. Sci. Engrg. C 16 (2001) 145. [16] H. Wang, S.P. Wong, W.Y. Cheung, N. Ke, G.H. Wen, X.X. Zhang, W.M. Kwok, J. Appl. Phys. 88 (2000) 4919. [17] H. Wang, S.P. Wong, W.Y. Cheung, N. Ke, M.F. Chiaf, H. Liu, X.X. Zhang, J. Appl. Phys. 88 (2000) 2063. [18] H. Wang, S.P. Wong, W.Q. Li, M.F. Chiaf, C.Y. Poon, W.Y. Cheung, N. Ke, Thin Solid Films 405 (2002) 304.
Structure, magnetic and electrical properties of soft magnetic Co–C amorphous thin films Hao Wang a,b,∗ , M.F. Chiah c , W.Y. Cheung c , S.P. Wong c a Key Laboratory for Thin Film and Microfabrication of Ministry of Education, Research Institute of Micro/Nanometer Science and
Technology, Shanghai Jiao Tong University, Shanghai 200030, PR China b Faculty of Physics and Electronic Technology, Hubei University, Wuhan 430062, PR China c Department of Electronic Engineering and Materials Science and Technology Research Center, The Chinese University of Hong Kong,
Shatin, N.T., Hong Kong, PR China Received 25 March 2003; accepted 10 July 2003 Communicated by J. Flouquet
Abstract Amorphous Cox C1−x thin films, with x in the range of 60–75% in atomic percentage, have been prepared by pulsed filtered vacuum arc deposition. The structures of the films were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The in-plane magnetic hysteresis loops were measured by a superconducting quantum interference device magnetometer at room temperature. The electrical transport properties were measured by the four-probe technique at various temperatures ranging from 20 to 300 K. The films were found to be magnetically soft with coercivities in the range of 2 to 12 Oe, resistivities in the range of 130 to 300 µ cm, and magnetic saturation flux densities in the range of 6 to 13 kG. The films also showed good thermal stability in their structural, electrical and magnetic properties upon annealing up to 200 ◦ C in a vacuum furnace. 2003 Elsevier B.V. All rights reserved. PACS: 75.50.Kj; 75.70.-i; 75.50.Ss Keywords: Magnetic properties; Resistivity; Microstructure; Co–C films; Magnetic recording
With the increase of magnetic recording area density, high coercivity media and high data rates are needed. As a consequence, it brings challenges to write head performance to write high coercivity media at high frequencies. The general requirements for thin film head core material are high saturation flux density (Bs ) to generate high field without saturation
* Corresponding author.
E-mail address: [email protected] (H. Wang). 0375-9601/$ – see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0375-9601(03)01135-6
of the core, low coercivity (Hc ) to reduce magnetic hysteresis loss, reasonable high permeability (µ) to be used at high frequency, high resistivity (ρ) to suppress eddy currents, high anisotropy (Hk ) to eliminate ferromagnetic resonance loss, zero magnetostriction (λs ) to ensure the magnetic field not producing stress in the film, high Curie temperature (Tc ) to sustain thermal stability, and good corrosion resistance to survive fabrication and file requirements. So far, the core material for commercial write head is electroplated permalloy developed by IBM in 1991
H. Wang et al. / Physics Letters A 316 (2003) 122–125
[1]. However, the moderate Bs (9–10 kG) and low ρ (20–25 µ cm) may limit its applications in the case of ultra high-density recording. The traditionally only choice of high frequency bulk core material is ferrite for its high ρ value, but it is not suitable for magnetic integrated circuit and thin film head applications due to the low Bs , low initial µ, and low Tc [2]. FeXN (X = Al, Zr, Ta, V, Ti, W, Hf) films have very high Bs (∼20 kG) and poses great potential as write head core materials for ultra high-density magnetic recording applications [3–6]. However, these films have been known to have problems at high frequencies due to the moderate ρ (∼100 µ cm). The very high Bs (20–21 kG) and near zero λs properties of Co rich CoFe and CoNiFe alloys make them promising materials for future write head core applications [7–9]. However, they are also metallic and sensitive to corrosion, which significantly lower their competitiveness for high frequency applications. Another attractive candidate developed more recently is the nanogranular or nanocomposite thin films, such as Fe–Al–O, Co–SiO2 , Co–Al–O, Co–Zr–O, Co–MF2 , CoFe–O, and CoFe–B–O [2,10–13]. These films consist of high moment transition metal or alloy nanograins encapsulated in an insulating matrix, which can have very high ρ in the range of 102 – 108 µ cm (depending on composition), good for GHz data rates applications. However, there are also problems with the nanogranular films. For examples, there is inherent trade-off between high ρ and low Hc and that between high ρ and high Bs . In this Letter, we shall report the structural, magnetic and electrical properties of Co–C granular films prepared by pulsed filtered vacuum arc deposition. Thin Cox C1−x (x = 60–75 at%) films of 20–27 nm thickness were prepared by a 3-source pulsed filtered vacuum arc deposition system, of which the details have been described elsewhere [14,15]. Two adjacent sources with pure graphite and cobalt as the cathode materials were operated simultaneously in a pulsed mode with a pulse duration of 2.5 ms. The substrate was placed at the center of the chamber facing to the bisector of the two sources and a negative bias voltage of −80 V was applied. The composition of the Co–C films was varied by adjusting the arc discharge conditions and was monitored by the integrated charges arriving at the sample holder from the respective arc sources. The as-deposited films were an-
123
Fig. 1. TEM plan-view bright field (BF) micrographs and electron diffraction (ED) pattern (insert) for the as-deposited Co65 C35 film.
nealed in a vacuum furnace (∼8 × 10−4 Pa) at various temperatures ranging from 200 to 400 ◦ C for 1 h to see the thermal annealing effects on the structural and magnetic properties. The composition of the films was determined by non-Rutherford backscattering spectrometry (NRBS). The microstructures of the films were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and Xray photoelectron spectroscopy (XPS). The magnetic properties were measured by a SQUID magnetometer. The resistivity was measured by the conventional fourprobe technique. Carbon coated Cu grids and Si (100) wafers with 50 nm thermally grown SiO2 on top were used as the substrates. Samples on copper grids were used for TEM studies, and those on Si substrates were used for the other measurements. Both TEM and XRD results showed that the asdeposited Cox C1−x films were amorphous even the carbon concentration was as high as 75% in atomic ratio. Fig. 1 is the plan-view bright field (BF) micrographs and electron diffraction (ED) pattern (insert) for the as-deposited Co65 C35 film. As shown in Fig. 1, the ED pattern shows halos, indicating that the film is amorphous. The BF micrograph shows granular structure though the contrast is weak. Judging from the micrograph, the typical granule size is about 3–4 nm. As reported in our previous papers [16,17], upon thermal annealing to a temperature (dependent on composition) between about 250 to 350 ◦ C, the as-deposited amorphous films went through a metastable stage at which a cobalt carbide phase and the
124
H. Wang et al. / Physics Letters A 316 (2003) 122–125
Fig. 2. XRD patterns for the Co70 C30 films, as-deposited and annealed at 300 and 400 ◦ C.
hexagonal close-packed (hcp) crystalline cobalt phase co-existed according to the TEM ED patterns. Upon further annealing to a sufficiently higher temperature (dependent on composition) between about 350 to 400 ◦ C, the carbide phase decomposed into hcp crystalline cobalt grains and graphite-like carbon. Such a change in crystalline phase against thermal treatment for these Co–C systems was also verified by XRD experiments. Typically, Fig. 2 is the X-ray diffraction pattern for the Co70 C30 film. The as-deposited sample shows a broadened peak centered at about 44◦ , indicating an amorphous-like structure. Also shown in Fig. 2 are the XRD patterns for the annealed samples. After annealing at 300 ◦ C, small diffraction peaks originating from hcp Co and δ –Co2 C appear, showing the co-existence of nanocrystals for the two phases in the film. Upon further increase of annealing temperature to 400 ◦ C, only those diffraction peaks belonging to hcp Co are observed due to the complete decomposition of the metastable carbide phase. On the other hand, XPS is helpful for the understanding of the phase transition of Cox C1−x films against thermal annealing. While the binding energies of the Co–2p peak in pure cobalt and cobalt carbides almost coincide with each other, those of the C–1s peak in cobalt carbide and amorphous carbon or graphite are different. Fig. 3 shows the C–1s spectra for the Co75 C25 film, as-deposited and annealed at various temperatures. The spectra were deconvoluted into two Gaussian peaks centered at about 283.1 and 284.5 eV, respectively. The peak at 283.1 eV corre-
Fig. 3. C–1s spectrum for the Co75 C25 film, the as-deposited and annealed at 300 and 400 ◦ C. The solid lines are experimental data and the dash lines are fitting results.
sponds to the binding energy of C–1s in cobalt carbide, and the peak at 284.5 eV corresponds to that of carbon–carbon bonds. As shown in Fig. 3, both carbide bonds and C–C bonds exist in the samples, asdeposited and annealed at 300 ◦ C. For the sample annealed at 400 ◦ C, the C–1s spectrum basically consists of only one peak at about 284.5 eV corresponding to C–C bonds, indicating the complete decomposition of the carbide phase. The in-plane magnetic hysteresis loops for the Cox C1−x films show that the as-deposited amorphous films are magnetically soft. The round shape hysteresis loops with squareness (remaneance ratio) smaller than 0.28 were observed in the films with Co content smaller than 65 at%. On the other hand, rectangular hysteresis loops with squareness in the range of 0.98 to 1 were obtained in the films with Co content larger than 70 at% [16]. Fig. 4 is the saturation flux density and coercivity as functions of Co concentration for the amorphous Cox C1−x films. With increasing Co concentration, while Bs increases almost linearly, Hc increases only slightly. The highest Bs value of 13 kG was achieved in the Co75 C25 film due to the largest amount of Co content. The slight increase of Hc with Co concentration maybe caused by the weak nanocrystallization of the Co grains leading to an enhancement of magnetocrystalline anisotropy.
H. Wang et al. / Physics Letters A 316 (2003) 122–125
125
In summary, we have prepared Cox C1−x (x = 60– 75 at%) thin films by pulsed filtered vacuum arc deposition. The as-deposited films are amorphous and magnetically soft. For a Co75 C25 film, the saturation flux density is 13 kG, the coercivity is 12 Oe, and the room temperature resistivity is 130 µ cm. The films are thermally stable upon vacuum annealing up to 200 ◦ C. These newly reported films may seek their applications as high-density magnetic recording head. Acknowledgements Fig. 4. The Bs and Hc as functions of Co concentration for the amorphous Cox C1−x films.
This work is supported in part by the Research Grants Council of Hong Kong SAR (Ref. No. CUHK4216/00E) and the China Education Ministry (Ref. No. 2001345). References
Fig. 5. The Co concentration dependence of resistivity for the as-deposited Cox C1−x films.
The temperature dependence of the resistivity for the amorphous Cox C1−x films showed metallic properties. The room-temperature resistivity is in the range of 130–300 µ cm, which is larger than those of magnetically soft alloys and FeN films. Fig. 5 shows the Co concentration dependence of room-temperature resistivity for these films. The resistivity increases with decreasing Co content. The ρ value is larger than 1000 µ cm when the Co content is smaller than about 35 at%. The microstructure results suggested that the high resistivity in the film is related to the partial surface oxidation of Co grains as inferred from the XPS results and the high resistivity of the amorphous carbon prepared by filtered vacuum arc deposition [14,18]. The as-deposited amorphous Cox C1−x films also showed good thermal stabilities in their structural, magnetic and electrical properties upon vacuum annealing up to 200 ◦ C.
[1] C. Tsang, M.M. Chen, T. Yogi, K. Ju, IEEE Trans. Magn. 26 (1990) 1689. [2] H. Fujimori, Scripta Metallurgica Materialia 33 (1995) 1625. [3] W.P. Jayasedara, S. Wang, M.H. Kryder, J. Appl. Phys. 79 (1996) 5880. [4] Y.K. Liu, M.H. Kryder, Appl. Phys. Lett. 77 (2000) 426. [5] V.R. Inturi, J.A. Barnard, J. Appl. Phys. 81 (1997) 4504. [6] L. Vrga, H. Jiang, T.J. Klemmer, W.D. Doyle, E.A. Payzant, J. Appl. Phys. 83 (1998) 5955. [7] C.L. Platt, A.E. Berkowitz, D.J. Smith, M.R. McCartney, J. Appl. Phys. 88 (2000) 2058. [8] T. Osaka, M. Takai, K. Hayashi, K. Ohashi, M. Saito, K. Yamada, Nature 392 (1998) 796. [9] X. Liu, P. Evans, G. Zangari, IEEE Trans. Magn. 36 (2000) 3479. [10] S. Ohnuma, H.J. Lee, N. Kobayashi, H. Fujimori, T. Masumoto, IEEE Trans. Magn. 37 (2001) 2251. [11] K.S. Kim, K.S. Byon, S.C. Yu, S.R. Kim, S.H. Han, Scripta Mater. 44 (2001) 1447. [12] Y.D. Zhang, S.H. Wang, D.T. Xiao, J.I. Budnick, W.A. Hines, IEEE Trans. Magn. 37 (2001) 2275. [13] G.S.D. Beach, A.E. Berkowitz, F.T. Parker, D.J. Smith, Appl. Phys. Lett. 79 (2001) 224. [14] S.P. Wong, H. Wang, N. Ke, W.Y. Cheung, M.F. Chiaf, D.H. Chen, Q.J. Li, H. Liu, X.X. Zhang, Int. J. Mod. Phys. B 14 (2000) 321. [15] H. Wang, S.P. Wong, W.Y. Cheung, N. Ke, W.F. Lau, M.F. Chiah, X.X. Zhang, Mater. Sci. Engrg. C 16 (2001) 145. [16] H. Wang, S.P. Wong, W.Y. Cheung, N. Ke, G.H. Wen, X.X. Zhang, W.M. Kwok, J. Appl. Phys. 88 (2000) 4919. [17] H. Wang, S.P. Wong, W.Y. Cheung, N. Ke, M.F. Chiaf, H. Liu, X.X. Zhang, J. Appl. Phys. 88 (2000) 2063. [18] H. Wang, S.P. Wong, W.Q. Li, M.F. Chiaf, C.Y. Poon, W.Y. Cheung, N. Ke, Thin Solid Films 405 (2002) 304.