Journal of Magnetism and Magnetic Materials 272–276 (2004) 1406–1407
Effects of the process parameters on the microstructure and
magnetic properties of nanocrystalline FeTaCN films
C.Y. Chou
a,*, P.C. Kuo
a, Y.D. Yao
b, S.C. Chen
c, C.T. Lie
a, A.C. Sun
aa
Institute of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan
b
Institute of Physics, Academia Sinica, Taipei 115, Taiwan
c
Department of Mechanical Engineering, De Lin Institute of Technology, Taipei 236, Taiwan
Abstract
FeTaCN films were prepared by DC-magnetron reactive co-sputtering of Fe target and TaC composite target with Ar þ N2sputtering gas. Effects of annealing temperature and sputtering power density of the Fe target on the magnetic
properties and microstructure of the FeTaCN film were investigated. Transmission electron microscopy analysis indicated that the FeTaCN film was nanocrystalline structure. The in-plane coercivity Hcjj is about 123 Oe and
saturation magnetization 4pMsis about 12215 kG for the as-deposited film.
r2003 Elsevier B.V. All rights reserved.
PACS: 75.50.Bb; 75.50.Kj; 75.70.Ak
Keywords: FeTaCN film; Soft magnetic; Nanocrystalline film
We have reported that the as-deposited FeTaCN film with nanocrystalline structure and good soft magnetic properties (in-plane coercivity Hcjj ¼ 122 Oe and
4pMs¼ 12214 kG) can be obtained by simultaneous
addition of C and N to FeTa alloy film as well as controlling the N2flow rate ratio and film thickness[1].
In this work, the effect of the sputtering power density of the Fe target ðSPDFeÞ on the magnetic properties and
microstructure of the FeTaCN thin film was investi-gated.
FeTaCN films were deposited on quartz substrates by DC-magnetron reactive co-sputtering of TaC composite target and Fe target at room temperature. The N2flow
rate ratio ðN2=Ar þ N2Þ in the sputtering gas was fixed
at 5%. The TaC composite target was made by Ta disk overlaid with C chips which covers 18% of the disk surface area. The sputtering power density of the TaC target was fixed at 1:97 W=cm2: The SPDFe was varied
from 3.2 to 4:44 W=cm2: The film thickness was fixed at 200 nm: An SiNx cap layer of about 20 nm was
deposited on the FeTaCN film to prevent the oxidation of magnetic film. After deposition, the films were post-annealed in vacuum below 1 105Torr for 30 min at
temperature between 200C and 500C; then quenched in ice water. Composition of the film was analyzed by X-ray photoelectron spectroscopy (XPS). The microstruc-ture and crystal strucmicrostruc-ture of the film were investigated by transmission electron microscopy (TEM). Magnetic properties of the films were measured by a vibrating sample magnetometer (VSM) at room temperature.
Fig. 1(a) and (b) shows the TEM bright field images and the corresponding selected area diffraction (SAD) patterns of the annealed Fe72:06Ta6:35C6:92N14:63 and
Fe77:75Ta5:85C6:16N10:25 films, respectively. The
anneal-ing temperature is 500C: The SPDFe is 3:7 W=cm2 for
the Fe72:06Ta6:35C6:92N14:63film and 4:44 W=cm2for the
Fe77:75Ta5:85C6:16N10:25 film. We can see that both
of the films have nanocrystalline structure, which consists of small a-Fe grains and more smaller Ta(C, N) precipitates. The average grain size of a-Fe is about 9 nm for the Fe72:06Ta6:35C6:92N14:63 film, which is
smaller than that of the Fe77:75Ta5:85C6:16N10:25 film.
The average grain size of a-Fe is about 11 nm for the Fe77:75Ta5:85C6:16N10:25film. During annealing at 500C;
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*Corresponding author. Tel.: 2-2364-8881; fax: +886-2-2363-4562.
E-mail address:a3150@ms3.hinet.net (C.Y. Chou).
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.141
the impeding of the a-Fe grain growth by high melting point TaC(N) precipitates was decreased as the SPDFe
was increased from 3.7 to 4:44 W=cm2: The decrease of the pinning effect of the TaC(N) precipitates results in the increase of a-Fe grain size. Since the magnetocrystal-line anisotropy is known to be averaged out by the refinement of grains, the coercivity of the film is decreased according to the random anisotropy model
[2]. Therefore, the randomly oriented fine a-Fe nano-grains together with TaC or TaN precipitates in the film will result to the low coercivity.
Fig. 2(a) and (b) shows the variations of the saturation magnetization 4pMs and in-plane coercivity
Hcjj with annealing temperature, respectively. In which
the FeTaCN films were deposited at different SPDFe:
We can see that the 4pMs value of the films was
increased with the SPDFeas shown inFig. 2(a). This is
due to the increase Fe content in the film or the increase of crystallinity of the film [3]. After anneal-ing at 500C; the 4pMs value is about 14 kG
when SPDFe is 3:2 W=cm2 (The film composition is
Fe69:22Ta7:07C8:53N15:18) and it will increase to 16 kG as
the SPDFe is increased to 4:44 W=cm2 (The film
composition is Fe77:75Ta5:85C6:16N10:25). FromFig. 2(b),
we can see that the Hcjj value could be decreased to
0:520:8 Oe if the film was annealed at 2002300C: This
is due to the stress relief resulting from the diffusing of C and N atoms out from a-Fe grains that will reduce the
Gibbs free energy [1]. After annealing at 500C; Hcjj
value of the film was increased slightly. The increase of Hcjj value was due to the large residual stress resulting
from quenching the film in ice water and the grain growth at high temperature annealing. As the grain grows, the larger value of the magnetocrystalline anisotropy results in higher value of the Hcjj [2].
In conclusion, 4pMsof the FeTaCN films is increased
with the SPDFe: The randomly oriented fine a-Fe
nanograins together with TaC or TaN precipitates in the film will result to the good soft magnetic properties.
This work was supported by the National Science Council and Ministry of Economic Affairs of ROC through Grant No. NSC 90-2216-E 002-036 and 92-EC-17-A-08-S1-0006, respectively.
References
[1] C.Y. Chou, et al., J. Appl. Phys. 93 (2003) 7205. [2] G. Herzer, IEEE Trans. Magn. 26 (1990) 1397. [3] M. Naoe, et al., IEEE Trans. Magn. 17 (1981) 3062.
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Fig. 1. TEM bright field image and electron diffraction pattern of the annealed (a) Fe72:06Ta6:35C6:92N14:63and (b) Fe77:75Ta5:85 C6:16N10:25films. 0 100 200 300 400 500 1 10 FeTaCN film, 200nm 3.2 W/cm2 3.95 W/cm2 3.46 W/cm2 4.2W/cm2 3.7 W/cm2 4.44 W/cm2 4 π Ms(kG) Hc // (Oe) Annealing Temperature(OC) 10 12 14 16 18 FeTaCN film, 200nm 3.2W/cm2 3.95 W/cm2 3.46 W/cm2 4.2 W/cm2 3.7W/cm2 4.44 W/cm2 (b) (a)
Fig. 2. Variations of (a) the saturation magnetization 4pMs and (b) the in-plane coercivity Hcjjwith annealing temperature
for the FeTaCN films with different SPDFe:
