Applied Surface Science 220 (2003) 30–39
Growth, structural, and magnetic properties of iron nitride
thin films deposited by dc magnetron sputtering
X. Wanga, W.T. Zhenga,*, H.W. Tiana, S.S. Yua, W. Xua, S.H. Mengb,
X.D. Heb, J.C. Hanb, C.Q. Sunc, B.K. Tayc
a
Department of Materials Science, Key Lab of Automobile Materials of MOE,
and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023, PR China
b
Research Institute of Composite Material, Harbin Institute of Technology, Harbin 150001, PR China
c
School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore
Received 29 October 2002; accepted 20 May 2003
Abstract
FeN thin films were deposited on glass substrates by dc magnetron sputtering at different Ar/N2 discharges. The composition,
structure and the surface morphology of the films were characterized using X-ray photoelectron spectroscopy (XPS), X-ray
diffraction (XRD), and atomic force microscopy (AFM). Films deposited at different nitrogen pressures exhibited different
structures with different nitrogen contents, and the surface roughness depended on the mechanism of the film growth. Saturation
magnetization and coercivity of all films were determined using superconducting quantum interference device, which showed
that if N2/(Ar þ N2 ) flow ratio was equal to or larger than 30% the nonmagnetic single-phase g00 -FeN appeared. If N2/(Ar þ N2 )
flow ratio was less than 10%, the films consisted of the mixed phases of FeN0.056 and g0 -Fe16N2, whose saturation magnetizations
were larger than that of a-Fe. If N2/(Ar þ N2 ) flow ratio was 10%, the phases of g0 -Fe4N and e-Fe3N appeared, whose saturation
magnetizations were lower than that of a-Fe.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Iron nitride thin films; Magnetron sputtering; Structure; Magnetic property
1. Introduction
Iron nitride films have received attention for many
years. Initially, they have been studied because of their
ability to improve surface hardness and wear resistance [1]. Recently, the FeN thin films have been
widely investigated since they show a variety of
structures and magnetic properties [2–23]. It is
known that nitrogen-poor phases such as g0 -Fe4N,
e-Fe2–3N, a0 -Fe8N and a00 -Fe16N2 are ferromagnetic
*
Corresponding author.
E-mail address: [email protected] (W.T. Zheng).
stoichiometric compounds, which are attractive substances for application as magnetic functional materials [24–26]. In particular, a00 -Fe16N2 phase is the most
important compound and can be a possible candidate
for high-density magnetic recording media owing to
its very high magnetic moment [11–13,27–29], which
is even larger than that of the pure a-Fe. The saturation
magnetization and the coercivity of these ferromagnetic phases for iron thin films have been studied by
many researchers [30–39], since the saturation magnetization is an intrinsic property of materials. Except
for the phases of a-Fe8N and a00 -Fe16N2, the saturation
magnetization of the other ferromagnetic phases is
0169-4332/$ – see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0169-4332(03)00752-9
X. Wang et al. / Applied Surface Science 220 (2003) 30–39
generally lower than that of the a-Fe, which has been
proved by most above-mentioned researchers. However, Ding et al. [40,41] found that both the saturation
magnetization and the coercivity of the FeN films with
any nitrogen content, grown using a reactive ion beam
sputtering method, were higher than those of pure iron
film. Furthermore, no direct relationship between the
higher saturation magnetization values and the phase
a0 þ a00 could be found in the as-synthesized iron
nitride films. On the other hand, as the coercivity is
an extrinsic property of material and is closely related
to the magnetic reversal mechanism for the samples,
different values are obtained for the same ferromagnetic phases. For example, in the case of e-Fe3N,
Leineweber et al. [22] failed to detect any significant
hysteresis effect at 4.5 K, and classified the phase as a
soft ferromagnetic material, while the coercivity of the
e-Fe3N deposited at 923.15 K by Takahashi et al. [38]
was found to be 9.01 mT (1132 Oe). Iwatsubo and
Naoe [30] observed that the coercivity was about
80 Oe, which was too large for a soft magnetic material. The various values of the coercivity for the same
phase were not fully understood. It might reasonably
be attributed to the concentration of nitrogen atoms in
the iron nitride thin films [30].
As to the nitrogen-rich phases, the cubic iron nitride
phase FeN has been paid much attention these years
[39], whose crystalline structure has been found to be
of ZnS-type with lattice parameters of a ¼ 0:4355 nm
(g-FeN) and/or NaCl-type with lattice parameters of
a ¼ 0:4524 nm (g-FeN). Due to nonmagnetic and
strong covalent nature of g00 -FeN, the iron nitride films
are expected to have low self-diffusion of iron. These
are two important requirements for the multilayer
superstructure of nuclear Bragg monochromator
[39,42–44]. Therefore, g00 -FeN films can be incorporated in the multilayer superstructure of nuclear Bragg
monochromator of type 56 FeN/57 FeN [44]. However,
although FeN films have many potential applications
and can be produced by many ways, preparing a pure
phase turned out to be rather difficult [44–47].
In this paper, using dc magnetron sputtering of pure
iron, we deposited iron nitride films on glass substrates
at room temperature by changing N2 flow rate in a
mixture of N2/Ar discharge. The composition, structure, surface roughness, and magnetic properties will
be explored as the N2 fraction in a mixture of N2/Ar
gas flow varies. In particular, the correlation among
31
the composition, structure, surface roughness, and
magnetic properties for the iron nitride films will be
investigated.
2. Experimental details
Iron nitride films were deposited on Corning glass
substrates in mixed Ar/N2 discharges using dc magnetron sputtering high purity (99.99%) a-iron (60 mm
in diameter). The distance between the substrate
holder and the target is 6.5 cm. The base pressure
was 5 105 Pa. Prior to deposition, the substrates
were cleaned ultrasonically in acetone and alcohol
consecutively, and then baked in a vacuum chamber at
250 8C for 2 h and cooled down to room temperature.
During sputtering, the dc power was kept constant
at 110 W, and the total pressure was fixed at 2.0 Pa.
At room temperature, the substrate holder was watercooled. The pure argon (99.999) and nitrogen (99.999)
gases were inlet into the chamber, controlled by two
independent mass-flow controllers. The argon gas flow
was fixed at 47.4 sccm, while the nitrogen fractions
in whole gas flow were 60% (N60), 50% (N50),
30% (N30), 10% (N10), 5% (N5), and 0% (N0),
respectively. The film thickness measurements were
carried out using Surface Profile Measuring System
(DEKTAK3). The thickness for all samples was found
to be about 200 nm, and the deposition rate is about
0.11 nm/s.
The structures of the films were analyzed using
X-ray diffraction (XRD) with Cu Ka radiation using
a current of 150 mA and voltage of 40 kV (Rigaku,
D/MAX-rA). The diffraction patterns were recorded
using a monochromatic wavelength l ¼ 0:15406 nm,
filtered by a graphite monochromator. The measurements were done in the range 20 2y 100 in the
y/2y mode with a 2y angle scanning rate of 0.02 8/s.
The experimental errors of the D2y was about 2%. To
determine the chemical binding state and composition,
X-ray photoelectron spectroscopy (XPS) (VG ESCALAB MK II) was performed with Mg Ka radiation and
hemisphere detector with an energy resolution of
0.5 eV, and power is given by emission of 15 mA
and voltage of 15 kV. Argon ion sputtering was used to
clean the surface. The surface morphology of the films
was characterized using atomic force microscopy
(AFM) (Digital Instruments Nanoscope III scanning
X. Wang et al. / Applied Surface Science 220 (2003) 30–39
probe microscopy). Magnetic properties of the films
were measured by SQUIDS magnetometer (MPMS5S, Quantum Design, San Diego, CA, USA) in magnetic fields up to 5 T with HgCo(NCS) and Ni as
standards. It is necessary to measure the film mass
precisely for evaluating the saturation magnetization.
The film mass was measured before and after the films
were dissolved in 15% HCl solution. The mass of
the samples was measured using analytical balance
(Sartorius BS210S).
N30
710.7
N60
710.7
Intensity ( A. U. )
32
N50
710.7
N10
711.0
707.8
707.3
N5
711.0
3. Results and discussion
705
3.1. Film composition and chemical bonding
The wide scan in XPS measurements for the FeN
samples can be used to determine the film composition, and the narrow scan to analyze the chemical
bonding among atoms. The wide scan of the samples
exhibits that the presence of a very small O 1s content.
The O 1s intensity decreased constantly with depth
during sputter cleaning of the film surface with Arþ
ions, consistent with the presence of a small amount of
oxygen-containing surface contamination. Table 1
lists the results of the atomic ratio of nitrogen atom
over iron atom and binding energies for the iron nitride
films deposited at N2 fraction of 60, 50, 30, 10, and 5%,
respectively. The nitrogen content (CN) is calculated
using the formula, CN ¼ ðIN SFe Þ=ðIFe SN þ IN SFe Þ,
where IN (IFe) is the intensity of N 1s (Fe 2p) peak,
and SN (SFe) is the sensitivity factor of element N (Fe). It
can be seen that the atomic ration of N/Fe for sample
N60, N50 and N30 is close to the ideal value for the
phase of FeN, and that for sample N10 is almost the
Table 1
Binding energies and atomic ratios for sample N60, N50, N30, N10
and N5
Samples
N 1s(eV)
Fe 2p2/3 (eV)
N/Fe
N60
N50
N30
396.7
396.5
396.9
710.7
710.7
710.7
1.06
1.19
1.10
N10
396.4
397.2
707.8
711.0
0.34
N5
396.3
397.2
707.3
711.0
0.11
710
715
720
725
730
Binding Energy (eV)
Fig. 1. X-ray photoelectron Fe 2p spectra for sample N60, N50,
N30, N10, and N5.
same as the value of e-Fe3N, since e-Fe3N is a dominant
phase compared to g0 -Fe4N in the film. As for the sample
N5, the atomic ratio N/Fe is 0.11, which is between the
value for a00 -Fe16N2 and the value for FeN0.056. Since
the N 1s signal is very weak in the XPS spectrum for the
film grown at N2 fraction of 5%, it is difficult to obtain
the precise value of atomic ratio N/Fe. Thus, the atomic
ratio of 0.11 only qualitatively indicates that the nitrogen content in FeN film is very low.
Figs. 1 and 2 show the XPS Fe 2p and N 1s spectra
for sample N60, N50, N30, N10 and N5. The most
prominent component of the Fe 2p peak (Fig. 1) for
sample N5 at binding energy of about 707.0 eV is
associated with Fe0 [46,47], while the peaks at about
710.7 eV or the higher energy in XPS Fe 2p3/2 spectra
for sample N60, N50, N30, N10 and N5 are related to
Fe2þ and Fe3þ [48–50]. XPS N 1s spectra (Fig. 2) for
the sample N60, N50 and N30 show a pronounced
peak at about 396.7 eV, while XPS N 1s spectra for
sample N10 and N5 exhibit two components which are
in the range of 396.3–397.9 eV, as shown in Fig. 2. All
these N 1s peaks correspond to a nitride layer [48–50].
The different N 1s bonding energies represent the
different environments around the nitrogen atoms in
the film. For sample N60, N50 and N30, there is only
one main peak for Fe 2p and N 1s, which means the
presence of only one chemical bonding state in the
film. However, as for the sample N10 and N5, there are
X. Wang et al. / Applied Surface Science 220 (2003) 30–39
more than one peak for Fe 2p and N 1s, which
indicates the presence of more than one chemical
bonding state in the film. From the XPS N 1s spectra
it can also be seen that the intensities of the N 1s peaks
decrease sharply as N2 fraction decreases. This is due
to the decrease in nitrogen content in the films with
decreasing the N2 fraction. The inaccuracy in all the
peak position is estimated to be 0.05 eV.
396.5
Intensity ( A. U. )
396.7
N50
396.9
396.4
N60
N30
397.2
3.2. Film structure
N10
396.3
396
33
397.2
N5
398
400
402
Binding Energy ( eV )
Fig. 2. X-ray photoelectron N 1s spectra for sample N60, N50,
N30, N10, and N5.
Fig. 3 shows the XRD patterns of the FeN films
deposited on glass substrates at different N2 fractions.
The diffraction spectra of sample N60, N50, and N30
could be indexed as belonging to new cubic-type
nitrides (FeN), Fe3þ cations in the fcc g00 -ZnS type
structure with lattice parameter of a ¼ 0:4310 0:0001 nm, which is slightly smaller than the value
Fig. 3. The XRD spectra for iron nitride films grown at different N2 fraction.
34
X. Wang et al. / Applied Surface Science 220 (2003) 30–39
of 0.4355 nm obtained by Rissanen et al. [46]. It
can be seen that this single phase of FeN is formed
when the N2 fraction is equal to or above 30%. All the
samples have preferred orientation of FeN(1 1 1).
With increasing N2 fraction in N2/Ar mixture gasflow rate, the intensities of the phase FeN(2 0 0),
FeN(2 2 0) and FeN(2 2 2) decrease, and the width
of the FeN(1 1 1) peak also decreases. When N2
Fig. 4. Atomic force microscope images for sample N30, N10, and N5, respectively. (a) The image for sample N30, (b) the image for sample
N10, (c) the image for sample N5.
X. Wang et al. / Applied Surface Science 220 (2003) 30–39
fraction decreases to 10%, the magnetic phases of
e-Fe3N with hcp structure and e-Fe4N with fcc structure appear. The lattice parameters for e-Fe3N are
a ¼ 0:4698 0:0001 nm, c ¼ 0:4379 0:0001 nm
(space group: P6322), while that for g0 -Fe4N is a ¼
0:3795 0:0001 nm. The lattice constants of e-Fe3N
and g0 -Fe4N are in agreement with those Kiriake
et al. [31] reported. The mixture phases of FeN0.056
(tetragonal structure with the lattice parameters, a ¼
0:2859 nm and c ¼ 0:3016 nm) and a00 -Fe16N2 (bct
structure with the lattice parameters, a ¼ 0:5720 nm
and c ¼ 0:6290 nm) are formed for the film deposited
at N2 fraction of 5%. The two small X-ray diffraction
peaks present at the 2y positions of about 44.5
and 77.98 are due to the a -Fe16N2(2 2 0) and
a00 -Fe16N2(1 0 5). At N2 fraction of 0 (only Ar gas
discharge), the films contain only a single phase of
a-Fe. Its lattice constant equals the value of 0.2866 nm
for bulk a-Fe. The results from the structure analyses
in XRD are in agreement with what is obtained from
XPS spectra.
3.3. Film surface morphology
Fig. 4(a)–(c) shows the AFM images for sample
N30, N10, and N5 with the same thickness, respectively. The roughness rms as a function of N2 fraction
for an area of 4:5 mm 4:5 mm is given in Fig. 5. For
the film deposited at N2 fraction of 30%, the roughness
rms is 2.17 nm, which is almost as low as that of
Fig. 5. AFM roughness rms as a function of N2 fraction for FeN
films.
35
substrate (rms ¼ 1:97 nm). As for the samples grown
at N2 fraction of 10 and 5%, respectively, the roughness rms increases up to 4.20 and 11.40 nm, respectively. The different roughness for different samples
may be due to the different growth mechanism of
the iron nitride films. There are three types of film
growth morphologies: layer-by-layer growth, unstable
growth, and self-affine surface [51]. Solid films grown
under far from equilibrium conditions are predicted to
have self-affine surfaces, and the roughness can be
characterized by appealing to a dynamic form [51]: If
the height of the surface at a location x, and time t, is
described by a function h(x, t), its average correlations
g(r, t) may scale as
D
E
gðr; tÞ ½hðx; tÞ hðx þ r; t þ tÞ2
!
t
2a
(1)
¼ jrj f
jrja=b
where the angle brackets denote an ensemble average,
which is realized by an average over time t and position x. The exponent a in Eq. (1) is known as the
‘‘static scaling’’ exponent or ‘‘roughness exponent’’,
which is a measure of the surface roughness, s:
D
E1=2
sðLÞ ¼ ½hðx; tÞ hhi2
La ; for t @ La=b
where L is the length parameter. The parameter b is the
growth exponent, which describes the growth rate of
the surface width:
D
E1=2
sðtÞ ¼ ½hðx; tÞ hhi2
tb ; for t ! La=b
We refer to two models as being in the same
universality class if they share the same exponents
a and b in all dimensions. But many growth models,
such as Eden model, ballistic deposition, which have
different values of the growth exponents, all belong to
the KPZ universality class [52,53]. There is also an
exact scaling relation that characterizes the KPZ
problem, i.e. a þ ða=bÞ ¼ 2. The KPZ universality
class appears to describe the asymptotic behavior of
most local, random growth processes, which allow the
formation of overhangs or voids, and desorption is the
dominant relaxation process.
Our previous study [54] showed that for the iron
nitride film deposited at N2 fraction of being equal
to or greater than 30%, the values of a 0:39,
36
X. Wang et al. / Applied Surface Science 220 (2003) 30–39
b 0:28 0:01, and a þ ða=bÞ ¼ 2 were obtained,
which means that impinging atoms may stick overhangs, vacancies, and also on the tops of the substrate
atoms to lead to lateral growth of the FeN films. The
exponents belong to the KPZ universality class. For
the films grown at 10% N2 fraction for different
deposition times, a 0:56 and b 0:37 0:01 are
obtained. Although the exponents do not conform to
any of the presently known models, the a þ ða=bÞ 2
implied that the films growth probably also be controlled by the KPZ equation. The values of a 0.65,
b 0:53 0:02, and a þ ða=bÞ 2 observed at the
5% N2 fraction are in good agreement with the
improved KPZ exponents a 2/3, b 1/2, and
a þ ða=bÞ 2. In this improved model, Kardar [51]
considered the possibility of introducing an ordered
parameter describing the local degree of crystallinity,
and the application of Kolmogorov’s energy cascade
concepts leads to a 2/3, b 1/2, a þ ða=bÞ 2.
3.4. Magnetic properties
The magnetic measurements of sample N30, N50,
and N60 exhibit that they are nonmagnetic. Due to
strong covalent nature of Fe–N bonds, as mentioned as
above, the iron nitride films are expected to have low
0.08
0.008
N10
0.06
0.006
0.04
0.004
Long Moment (emu)
Long Moment (emu)
N0
0.02
0.00
-0.02
-0.04
-0.06
-0.08
-4000 -3000 -2000 -1000
(a)
0
0.000
-0.002
-0.004
-0.006
-0.008
1000 2000 3000 4000
Field (Oe)
0.002
-3000 -2000 -1000
0
1000
2000
3000
Field (Oe)
(b)
0.06
N5
Long Monent (emu)
0.04
0.02
0.00
-0.02
-0.04
-0.06
-4000 -3000 -2000 -1000
(c)
0
1000 2000 3000 4000
Field (Oe)
Fig. 6. Magnetization measurements for the sample N0, N10 and N5, respectively. (a) The hysteresis loop for sample N0, (b) the hysteresis
loop for sample N10, (c) the hysteresis loop for sample N5.
X. Wang et al. / Applied Surface Science 220 (2003) 30–39
260
240
220
Ms ( emu/g )
self-diffusion of iron. These are two important requirements for the multilayer superstructure of nuclear
Bragg monochromator [44]. Therefore, the films with
a g-ZnS type structure can be incorporated in the
multilayer superstructure of nuclear Bragg monochromator of type 56 FeN/57 FeN.
Fig. 6(a)–(c) show the in-plane hysteresis loops of
the sample N0, N10 and N5, respectively. The saturation magnetization of about 216 emu/g (1 emu ¼
103 A m2; 1 g ¼ 103 kg) for the sample N0 is
obtained in Fig. 6(a). This value is slightly lower than
the value of 1700 emu/cm3 (218 emu/g; 1 cm3 ¼
106 m3) for pure a-Fe thin film [55], which may
be due to the error in mass measurement of the film.
The hysteresis effect of the pure iron film of sample
N0 is detected, and its coercivity is 95 Oe (1 Oe ¼
(103/4p)A/m). The saturation magnetization of
the sample N10 is 130 emu/g, which is lower
than that of either the phase of e-Fe3N (153 emu/g,
r ¼ 7:204 g/cm3) or the g0 -Fe4N (186 emu/g, r ¼
7:242 g/cm3) [50,55,56]. Since the saturation magnetization of sample N10 is near to that of e-Fe3N, it may
lead to the speculation on that the phase of e-Fe3N is
dominant in sample N10. From Fig. 6(b), the coercivity of the sample N10 is determined as 160 Oe. In the
case of the sample N5, the saturation magnetization is
246 emu/g, which is higher than that of the pure iron
film. In Fig. 6(c), the SQUIDS measurements also
revealed a hysteresis loop with a coercivity of about
320 Oe. By using molecular beam epitaxial (MBE),
Sugita et al. [57] have grown single-crystal Fe16N2
films, whose coercivity is 10–50 Oe, while as for
Borsa et al. [58], the value for multiphase film containing a00 -Fe16N2 is about 200 Oe. Since the coercivity is
an extrinsic property of materials, the precise reason
for this discrepancy still needs to be made clear.
The saturation magnetization as a function of the
N2 fraction for the films is shown in Fig. 7. The higher
value of the saturation magnetization of the sample N5
is caused by the formation of a00 -Fe16N2, which has a
higher saturation magnetization than that of pure a-Fe,
whereas the lower value of saturation magnetization
for sample N10 is caused by the formation of e-Fe3N
and -Fe4N, which have lower saturation magnetization
values than that of pure a-Fe. These results are in
agreement with what Utsushikawa and Niizuma [55]
reported, and disagreement with the results Ding et al.
[40,41] obtained. Ding et al. [40,41] found that as long
37
200
180
160
140
120
0
2
4
6
8
10
N2 Fraction
Fig. 7. Saturation magnetization as a function of the N2 fraction for
FeN films.
as the iron nitride films were formed their saturation
magnetization is higher than that of pure e-Fe. They
attributed the rise in saturation magnetization to the
presence of nitrogen in iron lattice, not directly related
to the a0 þ a00 phase.
4. Conclusions
The iron nitride films on glass substrates can be
synthesized using dc magnetron sputtering of pure
iron in a mixture N2/Ar discharge, and different phases
of FeN films can be obtained through changing N2
fraction in a mixture of N2/Ar gas flow. If the N2
fraction is equal to or above 30%, the single nonmagnetic phase g00 -FeN is formed, whose surface is
smooth nearly as that of the substrate. The films with
the phase g00 -FeN may have a potential application as a
nuclear Bragg monochromator since they can be
incorporated in the multilayer superstructure of
nuclear Bragg monochromator of type 56 FeN/57 FeN.
When N2 fraction decreases to 10%, the magnetic
phases of e-Fe3N (hcp structure) and g0 -Fe4N (fcc
structure) appear, whereas the mixture phases of
FeN0.056 and a00 -Fe16N2 are formed for the film deposited at N2 fraction of 5%. The surface roughness
increases as N2 fraction decreases, which ascribes
38
X. Wang et al. / Applied Surface Science 220 (2003) 30–39
to the different growth mechanisms for the films
deposited at different N2 fraction. The higher value
of the saturation magnetization of the FeN film grown
at N2 fraction of 5% is caused by the formation of a00 Fe16N2, which has a higher saturation magnetization
than that of pure a-Fe, whereas the lower value of
saturation magnetization for the FeN film deposited
at N2 fraction of 10% is caused by the formation of
e-Fe3N and g-Fe4N, which have lower saturation
magnetization values than that of pure a-Fe.
Acknowledgements
Funding support by the Teaching and Research
Award Program for OYTHEI of MOE and the special
foundation for Ph.D. program in High Education
Institutes, P.R.C., from Ministry of Chinese Education
and the Tan Chin Tuan Fellowship at Nanyang
Technological University, Singapore, are gratefully
acknowledged.
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
A. Fry, Stahl Eisen 43 (1923) 12.
K.H. Jack, Proc. R. Soc. A208 (1951) 200.
T.K. Kim, M. Takahashi, Appl. Phys. Lett. 20 (1972) 492.
S. Okamoto, O. Kitakami, Y. Shimada, J. Appl. Phys. 85
(1999) 4952.
T. Kacsich, M. Niederdrenk, P. Schaaf, K.P. Lieb, U. Geyer,
O. Schulte, Surf. Coat. Technol. 93 (1997) 32.
M. Niederdrenk, P. Schaaf, K.P. Lieb, O. Schulte, J. Alloy.
Comp. 237 (1996) 81.
T. Weber, L. de-Wit, F.W. Saris, P. Schaaf, Thin Solid Films
279 (1996) 216.
W.Y. Ching, N.X. Yong, P. Rulis, Appl. Phys. Lett. 80 (2002)
2904.
Z. Hei, Z. Liu, X. Xu, D. Li, R. Guan, Acta Metall. Sinica 37
(2001) 697.
L.A. Chebotkevich, Y.D. Vorobev, I.V. Pisarenko, Phys. Solid
State 40 (1998) 650.
T. Hinomura, S. Nasu, Mater. Trans. JIM 39 (1998) 700.
T. Hinomura, S. Nasu, Hyperfine Inter. 111 (1997) 221.
T. Hinomura, S. Nasu, Phys. B 237/238 (1997) 557.
S. Kikkawa, J. Jpn. Inst. Met. 62 (1998) 1031.
H. Shinno, M. Uehara, K. Saito, J. Mater. Sci. 32 (1997) 2255.
S.T. Patton, B. Bhushan, Wear 202 (1996) 99.
O. Yoshida, J. Ishikawa, K. Endo, N. Kitaori, Jpn. J. Appl.
Phys. 36 (1997) 777.
T. Hinomura, S. Nasu, Nuovo Cimento D, vol. 18D, ser.1,
Italy, 1996, p. 253.
[19] K. Niizuma, Y. Shato, Y. Utsushikawa, IEEE Trans. J. Magn.
Jpn. 9 (1994) 100.
[20] H. Shimojikkoku, K. Niizuma, Y. Utsushikawa, Trans. Inst.
Elec. Eng. Jpn. 114 (1994) 791.
[21] A. Morisako, K. Takahashi, M. Matsumoto, M. Naoe, J. Appl.
Phys. 63 (1988) 3230.
[22] A. Leineweber, H. Jacobs, W. Kockelmann, S. Hull, Phys. B
276/278 (2000) 266.
[23] H. Jacobs, A. Leineweber, W. Kockelmann, Mater. Sci.
Forum 325/326 (2000) 117.
[24] S. Grachev, D.M. Borsa, S. Vongtragool, D.O. Boerma, Surf.
Sci. 482/485 (2001) 802.
[25] A. Leineweber, H. Jacobs, F. Huning, H. Lueken, H. Schilder,
W. Kockelmann, J. Alloy. Comp. 288 (1999) 79.
[26] C. Chang, J.M. Sivertsen, J.H. Judy, et al., IEEE Trans. Mag.
MAG-23, 5 (1987).
[27] M. Takahashi, H. Shoji, J. Magn. Magn. Mater. 208 (2000)
145–157.
[28] C. Ortiz, G. Dumpich, A.H. Morrish, Appl. Phys. Lett. 65
(1994) 2737.
[29] M. Gupta, A. Gupta, P. Bhattacharya, et al., J. Alloy. Comp.
326 (2001) 265.
[30] S. Iwatsubo, M. Naoe, Vacuum 66 (2002) 251.
[31] W. Kiriake, K. Kuwahara, H. Iwanaga, Surf. Coat. Technol.
98 (1998) 1293.
[32] L. Rissanen, H. Jacobs, F. Huning, et al., J. Alloy Comp. 316
(2001) 21.
[33] D.H. Mosca, S.R. Teixeria, P.H. Dionisio, et al., J. Appl. Phys.
69 (1991) 261.
[34] D.H. Mosca, P.H. Dionisio, W.H. Schreiner, et al., J. Appl.
Phys. 67 (1990) 7514.
[35] J.M.D. Coey, P.A.I. Smith, J. Magn. Magn. Mater. 200 (1999)
405.
[36] Y. Sugita, H. Takahashi, M. Komuro, J. Appl. Phys. 76 (1994)
6637.
[37] N.D. Telling, G.A. Jones, P.J. Grundy, J. Magn. Magn. Mater.
226/230 (2001) 1659.
[38] N. Takahashi, Y. Toda, T. Nakamura, Mater. Lett. 42 (2000)
380.
[39] L. Rissanen, K.P. Lieb, M. Niederdrenk, O. Schulte, P.
Schaaf, in: Proceedings of the V50 International Conference
on the Application of the Mossbauer Effect, ICAME-95,
Ortalli, I.-Boloogna, Italy, 1996, p. 595.
[40] X.Z. Ding, F.M. Zhang, Y.L. Sun, Y.L. Zhou, J.S. Yan, H.L.
Shen, X. Wang, X.H. Liu, D.F. Shen, Surf. Coat. Technol.
103/104 (1998) 156.
[41] X.Z. Ding, F.M. Zhang, J.S. Yan, H.L. Shen, X. Wang, X.H.
Liu, D.F. Shen, J. Appl. Phys. 82 (1997) 5154.
[42] A.I. Chumakov, G.V. Smimov, A.Q.R. Baron, J. Arthur, D.E.
Brown, S.L. Ruby, G.S. Brown, N.N. Salashehenko, Phys.
Rev. Lett. 71 (1993) 2489.
[43] R. Rohlsberger, E. Witthoff, E. Gerdau, E. Loken, J. Appl.
Phys. 74 (1993) 1933.
[44] M. Gupta, A. Gupta, S.M. Chaudhari, et al., Vacuum 60
(2001) 395.
[45] L. Rissanen, P. Schaaf, M. Neubauer, et al., Appl. Surf. Sci.
138/139 (1999) 261.
X. Wang et al. / Applied Surface Science 220 (2003) 30–39
[46] L. Rissanen, M. Neubauer, K.P. Lieb, et al., J. Alloy. Comp.
274 (1998) 74.
[47] E.J. Miola, S.D. De Soua, P.A.P. Nascente, et al., Appl. Surf.
Sci. 144/145 (1999) 272.
[48] D.L. Cocke, M.J. Rajman, S. Veprek, J. Electrochem. Soc.
136 (1989) 3655.
[49] W. Diekmann, G. Panzner, H.J. Grabke, Surf. Sci. 218 (1989)
507.
[50] H. Jacobs, D. Rechenbach, U. Zachwieja, J. Alloys Comp.
227 (1995) 10.
[51] M. Kardar, Phys. B. 221 (1996) 60.
39
[52] H.N. Yang, T.M. Lu, G.C. Wang, Phys. Rev. B. 47 (1993) 3911.
[53] I. Procaccia, M.H. Hensen, V.S. L’vov, K. Sneppen, R. Zeitak,
Phys. Rev. A. 46 (1992) 3220.
[54] X. Wang, W.T. Zheng, L.J. Gao, Mater. Phys. Chem., in press.
[55] Y. Utsushikawa, K. Niizuma, J. Alloy. Comp. 222 (1995) 188.
[56] T. Yamaguchi, M. Sakita, M. Nakamura, J. Magn. Magn.
Mater. 215/216 (2000) 529.
[57] Y. Sugita, K. Mitsuoka, M. Komuro, et al., J. Appl. Phys. 70
(1991) 5977.
[58] D.M. Borsa, S. Grachev, J.W.J. Kerssemakers, et al., J. Magn.
Magn. Mater. 240 (2002) 445–447.