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64Ni implantation in 57Fe thin films studied by RBS and CEMS techniques
Nuclear instruments and Methods in Physics Research B59/60 (1991) 833-836 worth-Holl~d
833
57Fe thin fifms studied by RBS and CEMS techniques G. Marest and M.A. ET Khakani Instirut de Physrque Nuci6aire de Lyon, IN2P3-CNRS F-696X? Yiileurhunne Cedex, France
el Unisersit6 Claude Bernar& 43 Bd du II Nnr:emhre 1918,
Thin films of 57Fe deposited on SQ substrates were implanted with 0.5, 2.5. 5 and 10X LO’”MNi/cm’. The implantation energy (80 keV) was calrulated to alter the whole thickness (70 run) of the samples. The “4Ni isotope was chosen for its good mass separation with 57Fe in the backscattering spectroscopy measurements (RBS) at 5.7 MeV a-particles. Thus the RBS technique was used to determine the nickel depth profiles in the implanted surface. Due to the high sputtering yield ( YNI,FU- 2). saturation is nearly reached for the highest implanted fluence. Conversion electron MBssbauer spectroscopy (CEMS) was used to identify various products of implantation. FeNi alloys with different ~om~sitions and structures are formed: Fe(Ni) solid solution. bee Fe-rich phase, fee Ni-rich zone and fee FeNi Invar
Among the numerous anomalies of the properties of Fe, _,Ni x alloys in the Invar region (0.3 <: x <: 0.4). the strong deviation of the saturation magnetization and of the iron hyperfine field N,r from the Slater-Pauling curve is very characteristic. However, no such discontinuity has been observed for sputtered films {If and for films prepared by simultaneous co-deposition of Ni and Fe [2]. As-prepared films show, in contrast to the behavior of bulk Fe, _ .Ni, samples, high magnetic moments and large mean hyperfine fields. After annealing around 850 K the films exhibit bulk behavior. As well, amorphous FeNi alloy films do not show the abrupt decrease of H,, around the Invar composition as for crystalline Fe-Ni alloys 13f. Moreover, it has been shown that crystalline sputter deposited films with extended lattices belong to a strong ferromagnetic state and lose the lnvar characteristic [3]. From all these studies it seems that the Invar behavior is correlated to the preparation procedure of the Fe-Ni alloys, For a better understanding of this magnetic behavior, other thin film alloying techniques such as ion beam mixing or ion implantation are of high interest. Recently, ion beam induced alloying of Fe-Ni bilayers has been studied 141. In addition to the two distinct phases identified as solid solutions of Ni in bet iron and Fe in fee nickel, an Fe-Ni Invar alloy formed in the mixed region exhibits deviation of the average iron hyperfine field from the Slater-Pauling curve. Ion implantation is a nonconventional technique to alloy different species by injecting energetic ians into
the surface of a material. In the present study nickd was implanted into iron films in order to study the resulting Fe-Ni alloys. The RBS technique was used to determine the depth profile distributions of nickel, since the Invar behavior is closely dependent on the nickel concentration [4]. Measurement of hyperfine interactions provides info~ation on symmetry, ordering, and chemical bonding in the immediate environment of the probed nucieus. Fe, _ .Ni, alloys have been extensively studied using Mirssbauer spectroscopy. Thus. using this technique it is possible to study the inhomogeneity of the local concentration in FeNi alloys [S-7]. For example, its sensitivity to distinguish an fee Fe-rich paramagnetic phase from the fee Ni-rich ferromagnetic phase constitutes a very interesting property [S]. Conversion electron Miissbauer spectroscopy (CEMS) is particularly suited for probing implanted thin films, as detected internal conversion electrons and Auger electrons are emitted from a - 150 nm thick layer.
Thin layers ( - 70 nm) of pure 57Fe were deposited on SQ substrates in Trento, Italy. They were implanted with 80 keV mNi ions using the isotope sep arator of the Institut de Physique Nucleaire de Lyon. This energy was chosen on the basis of TRIM calculations, in order to alter the whole thickness of iron samples. The calculated mean projected range for 80 keV 64Ni into iron is R, = 26 nm with a standard deviation h R, = 12 nm. Fluences were varied in the
~16g-5~3X/91/$03.~0 $2 1991 - Elsevier Science Publishers B.V. (North-Holland)
VII. METALS / T~I3OL~Y
G. Marest, M.A. El Khakani
834
/ “4N~ implantation
Channel Fig. 1. RBS spectrum
obtained
number
at 5.7 MeV He”+ particle energy for a 2.5 X 10lh h4 Ni/cm’ “Fe films. The solid line is the result of fitting the experimental
range (0.5-10) x 10’” ions/cm’. 64Ni isotope was used in implantation experiments for its good mass separation with 57Fe in RBS spectra. Indeed, for a 5.7 MeV He’+ particle energy with the detection angle set at f?,,, = 172O and for the considered thickness. RBS measurements were achieved without any interference between h4Ni and 57Fe signals (fig. 1). Experimental RBS spectra were fitted using a computing code based on the RBS theory and then 64Ni depth profiles were obtained, see fig. 2. CEMS spectra were determined at room temperature with the use of a flowing He-4% CH, gas proportional counter in which the sample was placed in a back-
7
\ \ A\
\
2.5E16
0 5.OE16 .
l.OEl7
1.
64Ni fluence [cmm2] Virgin IS [mm/s] HF
P-1
W [mm/s] RA
\
\
IS [mm/s]
6
HF PI
RA IS [mm/s] HF P-1
20 Depth Fig.
2.
30
RA
40
(W/d)
h4Ni depth profile distributions obtained technique for varitis fluences.
IS [mm/s] by the RBS
at 80 keV into thin
Table 1 Hyperfine parameters of 5’Fe thin films implanted to various splitting fluences of wNi. Isomer shifts (IS) and quadrupole (QS) are in mm/s. hyperfine fields (HF) are in Tesla, and RA represents the relative area of each component. HF represents the mean value of the hyperfine field distribution
. 5.OE15 *
fluence implanted spectrum.
scattering geometry. The 57CoRh source was mounted on a constant acceleration triangular-motion velocity transducer. For spectra analysis a program developed by Le Caer et al. 191 was used in order to determine the P(H) as well as a standard hyperfine field distribution of Lorentzian fitting program assuming a superposition lines.
Fluonce : ( “NiNi’/cm2) \
in ‘7Fe thin films
QS [mm/s1 RA
0
33.0 0.20
1.oo
5 X 10”
2.5 x 10lh
5 x 10’”
10”
+ 0.01
0.01
33.2 0.26 0.39
33.3 0.31 0.42
0.01 33.2 0.33 0.35
0.02 33.3 0.34 0.21
0.03 34.3 0.49
0.02 34.4 0.31
0.02 34.4 0.23
0.01 34.5 0.15
0.04
0.10
0.09
0.10
23.0 0.12
23.2 0.25
24.5 0.40
23.3 0.61
0.38 0.65 0.02
0.32 1.22 0.02
0.32 1.12 0.02
G. Mares& M.A. El Khakani
/ 04Ni tmplanration
3. Results and discussion
When the fluence is increased (0.5 up to 10 X 1016 h4Ni/cm2) the maximum of the nickel distribution increases as well (from - 2 to 16 at.%) and is shifted towards the surface. The shape of the profile for the highest fluence shows that there is pronounced evidence of sputtering. From RBS measurements achieved on thin iron films before and after implantation, the iron sputtering yield was deduced ( YNIjFe = 2.6 + 0.6) in good agreement with TRIM prediction (Y,, = 2.0). Due to this high iron sputtering yield, saturation is nearly reached for the 1017 64Ni/cm2 fluence. From the literature it is known that the hyperfine field in a Fe-Ni alloy, depending upon its composition and structure, can vary from 0 to about 35 T [1,2,10].
in j7Fe thin films
835
Therefore, as a result of Ni implantation, one can expect a field distribution in the Massbauer spectra of implanted samples due to the local concentration distribution of nickel. Fig. 3 shows the conversion electron Massbauer spectra of the specimens implanted with various fluences. The results obtained with a continuous h,, distribution and with the standard fitting program were consistent, since discrete hyperfine fields corresponded to the most intense peaks of the field distribution. The main hyperfine parameters are given in table 1. The hyperfine parameters of pure iron change slightly with increasing fluence, indicating formation of a solid soiution of Ni in Fe 1111. In addition, a well defined ferromagnetic phase (H,, = 34.4 T) begins to appear. It corresponds to a bee iron-rich Fe-Ni alloy [12]. More-
2.4 2.2 1.8 ::
1.4
z ifi 2
1.0 2.4
Y 5 ;
2.2 1.8 1.4 1.0
1.6 1.4 1.2 1.0
1.4
1.2
1.0. -8
-6
-4
-2
0
VELOCITY
2
4
6
(mrn.$)
8
0
10
20
30
40
H(T)
Fig. 3. CEMS spectra corresponding to thin “Fe films implanted with (a) 5 X 1015.(b) 2.5 X 10”. (cf 5 X 1016 and (d) 10” 64Ni+/cm2, and their associated hyperfine field dist~butions P(H) in which the component with H = 33 T has been subtracted. VII. METALS
/ TRIBOLOGY
836
G. Marest. M.A. El Khukani /
over, two weak peaks located at 17 and 5 T in the P(H) distribution are the signature of fee Fe-.Ni phases, of which the magnetization deviates from the Slater-Pauling curve. When the fluence # is increased, P( If) broadens always with a mean hyperfine field value around 23 T, a characteristic value for Invar alloys [7,12,13]. In the case of a non-Invar Fe-Ni alloy, P(H) is very narrow, centered around a discrete value of H, whereas for an Invar alloy the distribution is widened toward the low field values [13]. The present P(H) distributions are similar to distributions obtained for Invar Fe, _ ,Ni ~ alloys with 0.28 < x < 0.36. For $2 5 X 10’” ions/cm’ the intensities of the fields in the 22-32 T range. typical of Invar alloys, are clearly enhanced. A non-vanishing P(H) contribution at H = 0 T could correspond to the presence of a non-magnetic fee phase. Indeed. it is known that Fe, _ .Ni ~ Invar alloys with 0.3 < _X< 0.4 have a tendency to separate into two fee phases with different compositions: a ferromagnetic Ni-rich phase and a non-magnetic Fe-rich phase [8]. As soon as @ 2 2.5 x 10ih ions/cm2 a weak paramagnetic component appears. This component could be attributed to some surface oxidation or to recoiled iron atoms into the SiOz substrate during implantation.
4. Conclusions Nickel ion implantation into thin layers of iron leads to the formation of different Fe-Ni alloys with a tendency to form mainly phases exhibiting Invar behavior as the fluence is increased. From table 1 it can be seen that the percentage of the bee Fe-Ni phase decreases with increasing nickel fluence, as was the case when dose of Art was increased for ion beam mixing of Fe-Ni bilayers [4]. The hyperfine field distributions obtained in this study are similar to those obtained after ion beam mixing of Fe-Ni bilayers, from which a very narrow composition range (0.32 < x <: 0.34) was deduced 141. Otherwise, Fe,_,Ni, (0.32 < x < 0.39) alloy films obtained by simultaneous co-deposition of Ni and Fe and then annealed at 850 K exhibited rather similar P(H) distributions as in the present article (21. Then, from these comparisons. it is deduced that ion implan-
“Ni
implantatron
rn ‘%;e thin films
tation has produced Invar alloys (Fe, _.Ni, with x 0.35) whereas the maximum local concentration of nickel is never higher than 16 at.%. This could be explained by some short range diffusion processes leading to chemical clustering. Indeed, ion implantation in other systems often creates phases similar to those in the high temperature (700-~00 K) quenched alloys [14].
Acknowledgements The authors would like to express their thanks to Dr. C. Tosello (Trento) for providing samples and to Mr. A. Plantier for performing implantations. This work is a part of a research project financially supported by the Commission of the European Communities under contract SCI-00240C(A).
References PI K. Sumiyama. M. Kadono and Y. Nakamura. Trans. Jpn.
Inst. Met. 24 (1983) 190.
PI G. Dumpich. E. Becker, K. Schletz. W. Stamm. W. Keune, W. Kiauka and S. Murayama. J. Magn. Magn. Mater. 74 (1988) 237. [31 J. Arai. J. Appl. Phys. 64 (1988) 3143. [41 L.M. Gratton, A. Gupta. W. Keune. S. Lo Russo, .I. Parellada, G. Principi and C. Toseilo, Mater. Sci. Eng. A115 (1989) 161. [51 U. Comer, S. Nasu and W. Kappes. J. Magn. Magn. Mater. 10 (1979) 244. WI H. Ullrich and J. Hesse. J. Magn. Magn. Mater. 45 (1984) 315. I71 M. Shiga and Y. Nakamura, J. Magn. Magn. Mater. 40 (1984) 319. PI H. France and H.R. Rechenberg, J. Phys. FlS (1985) 719. 191 G. Le Caer and J.M. Dubois. J. Phys. El2 (1979) 1083. [lOI C.E. Johnson, MS. Ridout and T.E. Cranshaw. Proc. Phys. Sot. 81 (1963) 1079. 1111 B. Fultz and J.W. Morris Jr., Hyperfine Interactions 28 (1986) 553. 1121 H. Rechenberg, L. Billard, A. Chamberod and N. Natta, J. Phys. Chem. Solids 34 (1973) 1251. 1131 J.B. Mtiller and J. Hesse. Z. Phys. B54 (1983) 43. D4f H. Binczycka. B. Fornal, G. Marest. N. Moncoffre and J. Stanek. Radiat. Eff.. to be published.
833
57Fe thin fifms studied by RBS and CEMS techniques G. Marest and M.A. ET Khakani Instirut de Physrque Nuci6aire de Lyon, IN2P3-CNRS F-696X? Yiileurhunne Cedex, France
el Unisersit6 Claude Bernar& 43 Bd du II Nnr:emhre 1918,
Thin films of 57Fe deposited on SQ substrates were implanted with 0.5, 2.5. 5 and 10X LO’”MNi/cm’. The implantation energy (80 keV) was calrulated to alter the whole thickness (70 run) of the samples. The “4Ni isotope was chosen for its good mass separation with 57Fe in the backscattering spectroscopy measurements (RBS) at 5.7 MeV a-particles. Thus the RBS technique was used to determine the nickel depth profiles in the implanted surface. Due to the high sputtering yield ( YNI,FU- 2). saturation is nearly reached for the highest implanted fluence. Conversion electron MBssbauer spectroscopy (CEMS) was used to identify various products of implantation. FeNi alloys with different ~om~sitions and structures are formed: Fe(Ni) solid solution. bee Fe-rich phase, fee Ni-rich zone and fee FeNi Invar
Among the numerous anomalies of the properties of Fe, _,Ni x alloys in the Invar region (0.3 <: x <: 0.4). the strong deviation of the saturation magnetization and of the iron hyperfine field N,r from the Slater-Pauling curve is very characteristic. However, no such discontinuity has been observed for sputtered films {If and for films prepared by simultaneous co-deposition of Ni and Fe [2]. As-prepared films show, in contrast to the behavior of bulk Fe, _ .Ni, samples, high magnetic moments and large mean hyperfine fields. After annealing around 850 K the films exhibit bulk behavior. As well, amorphous FeNi alloy films do not show the abrupt decrease of H,, around the Invar composition as for crystalline Fe-Ni alloys 13f. Moreover, it has been shown that crystalline sputter deposited films with extended lattices belong to a strong ferromagnetic state and lose the lnvar characteristic [3]. From all these studies it seems that the Invar behavior is correlated to the preparation procedure of the Fe-Ni alloys, For a better understanding of this magnetic behavior, other thin film alloying techniques such as ion beam mixing or ion implantation are of high interest. Recently, ion beam induced alloying of Fe-Ni bilayers has been studied 141. In addition to the two distinct phases identified as solid solutions of Ni in bet iron and Fe in fee nickel, an Fe-Ni Invar alloy formed in the mixed region exhibits deviation of the average iron hyperfine field from the Slater-Pauling curve. Ion implantation is a nonconventional technique to alloy different species by injecting energetic ians into
the surface of a material. In the present study nickd was implanted into iron films in order to study the resulting Fe-Ni alloys. The RBS technique was used to determine the depth profile distributions of nickel, since the Invar behavior is closely dependent on the nickel concentration [4]. Measurement of hyperfine interactions provides info~ation on symmetry, ordering, and chemical bonding in the immediate environment of the probed nucieus. Fe, _ .Ni, alloys have been extensively studied using Mirssbauer spectroscopy. Thus. using this technique it is possible to study the inhomogeneity of the local concentration in FeNi alloys [S-7]. For example, its sensitivity to distinguish an fee Fe-rich paramagnetic phase from the fee Ni-rich ferromagnetic phase constitutes a very interesting property [S]. Conversion electron Miissbauer spectroscopy (CEMS) is particularly suited for probing implanted thin films, as detected internal conversion electrons and Auger electrons are emitted from a - 150 nm thick layer.
Thin layers ( - 70 nm) of pure 57Fe were deposited on SQ substrates in Trento, Italy. They were implanted with 80 keV mNi ions using the isotope sep arator of the Institut de Physique Nucleaire de Lyon. This energy was chosen on the basis of TRIM calculations, in order to alter the whole thickness of iron samples. The calculated mean projected range for 80 keV 64Ni into iron is R, = 26 nm with a standard deviation h R, = 12 nm. Fluences were varied in the
~16g-5~3X/91/$03.~0 $2 1991 - Elsevier Science Publishers B.V. (North-Holland)
VII. METALS / T~I3OL~Y
G. Marest, M.A. El Khakani
834
/ “4N~ implantation
Channel Fig. 1. RBS spectrum
obtained
number
at 5.7 MeV He”+ particle energy for a 2.5 X 10lh h4 Ni/cm’ “Fe films. The solid line is the result of fitting the experimental
range (0.5-10) x 10’” ions/cm’. 64Ni isotope was used in implantation experiments for its good mass separation with 57Fe in RBS spectra. Indeed, for a 5.7 MeV He’+ particle energy with the detection angle set at f?,,, = 172O and for the considered thickness. RBS measurements were achieved without any interference between h4Ni and 57Fe signals (fig. 1). Experimental RBS spectra were fitted using a computing code based on the RBS theory and then 64Ni depth profiles were obtained, see fig. 2. CEMS spectra were determined at room temperature with the use of a flowing He-4% CH, gas proportional counter in which the sample was placed in a back-
7
\ \ A\
\
2.5E16
0 5.OE16 .
l.OEl7
1.
64Ni fluence [cmm2] Virgin IS [mm/s] HF
P-1
W [mm/s] RA
\
\
IS [mm/s]
6
HF PI
RA IS [mm/s] HF P-1
20 Depth Fig.
2.
30
RA
40
(W/d)
h4Ni depth profile distributions obtained technique for varitis fluences.
IS [mm/s] by the RBS
at 80 keV into thin
Table 1 Hyperfine parameters of 5’Fe thin films implanted to various splitting fluences of wNi. Isomer shifts (IS) and quadrupole (QS) are in mm/s. hyperfine fields (HF) are in Tesla, and RA represents the relative area of each component. HF represents the mean value of the hyperfine field distribution
. 5.OE15 *
fluence implanted spectrum.
scattering geometry. The 57CoRh source was mounted on a constant acceleration triangular-motion velocity transducer. For spectra analysis a program developed by Le Caer et al. 191 was used in order to determine the P(H) as well as a standard hyperfine field distribution of Lorentzian fitting program assuming a superposition lines.
Fluonce : ( “NiNi’/cm2) \
in ‘7Fe thin films
QS [mm/s1 RA
0
33.0 0.20
1.oo
5 X 10”
2.5 x 10lh
5 x 10’”
10”
+ 0.01
0.01
33.2 0.26 0.39
33.3 0.31 0.42
0.01 33.2 0.33 0.35
0.02 33.3 0.34 0.21
0.03 34.3 0.49
0.02 34.4 0.31
0.02 34.4 0.23
0.01 34.5 0.15
0.04
0.10
0.09
0.10
23.0 0.12
23.2 0.25
24.5 0.40
23.3 0.61
0.38 0.65 0.02
0.32 1.22 0.02
0.32 1.12 0.02
G. Mares& M.A. El Khakani
/ 04Ni tmplanration
3. Results and discussion
When the fluence is increased (0.5 up to 10 X 1016 h4Ni/cm2) the maximum of the nickel distribution increases as well (from - 2 to 16 at.%) and is shifted towards the surface. The shape of the profile for the highest fluence shows that there is pronounced evidence of sputtering. From RBS measurements achieved on thin iron films before and after implantation, the iron sputtering yield was deduced ( YNIjFe = 2.6 + 0.6) in good agreement with TRIM prediction (Y,, = 2.0). Due to this high iron sputtering yield, saturation is nearly reached for the 1017 64Ni/cm2 fluence. From the literature it is known that the hyperfine field in a Fe-Ni alloy, depending upon its composition and structure, can vary from 0 to about 35 T [1,2,10].
in j7Fe thin films
835
Therefore, as a result of Ni implantation, one can expect a field distribution in the Massbauer spectra of implanted samples due to the local concentration distribution of nickel. Fig. 3 shows the conversion electron Massbauer spectra of the specimens implanted with various fluences. The results obtained with a continuous h,, distribution and with the standard fitting program were consistent, since discrete hyperfine fields corresponded to the most intense peaks of the field distribution. The main hyperfine parameters are given in table 1. The hyperfine parameters of pure iron change slightly with increasing fluence, indicating formation of a solid soiution of Ni in Fe 1111. In addition, a well defined ferromagnetic phase (H,, = 34.4 T) begins to appear. It corresponds to a bee iron-rich Fe-Ni alloy [12]. More-
2.4 2.2 1.8 ::
1.4
z ifi 2
1.0 2.4
Y 5 ;
2.2 1.8 1.4 1.0
1.6 1.4 1.2 1.0
1.4
1.2
1.0. -8
-6
-4
-2
0
VELOCITY
2
4
6
(mrn.$)
8
0
10
20
30
40
H(T)
Fig. 3. CEMS spectra corresponding to thin “Fe films implanted with (a) 5 X 1015.(b) 2.5 X 10”. (cf 5 X 1016 and (d) 10” 64Ni+/cm2, and their associated hyperfine field dist~butions P(H) in which the component with H = 33 T has been subtracted. VII. METALS
/ TRIBOLOGY
836
G. Marest. M.A. El Khukani /
over, two weak peaks located at 17 and 5 T in the P(H) distribution are the signature of fee Fe-.Ni phases, of which the magnetization deviates from the Slater-Pauling curve. When the fluence # is increased, P( If) broadens always with a mean hyperfine field value around 23 T, a characteristic value for Invar alloys [7,12,13]. In the case of a non-Invar Fe-Ni alloy, P(H) is very narrow, centered around a discrete value of H, whereas for an Invar alloy the distribution is widened toward the low field values [13]. The present P(H) distributions are similar to distributions obtained for Invar Fe, _ ,Ni ~ alloys with 0.28 < x < 0.36. For $2 5 X 10’” ions/cm’ the intensities of the fields in the 22-32 T range. typical of Invar alloys, are clearly enhanced. A non-vanishing P(H) contribution at H = 0 T could correspond to the presence of a non-magnetic fee phase. Indeed. it is known that Fe, _ .Ni ~ Invar alloys with 0.3 < _X< 0.4 have a tendency to separate into two fee phases with different compositions: a ferromagnetic Ni-rich phase and a non-magnetic Fe-rich phase [8]. As soon as @ 2 2.5 x 10ih ions/cm2 a weak paramagnetic component appears. This component could be attributed to some surface oxidation or to recoiled iron atoms into the SiOz substrate during implantation.
4. Conclusions Nickel ion implantation into thin layers of iron leads to the formation of different Fe-Ni alloys with a tendency to form mainly phases exhibiting Invar behavior as the fluence is increased. From table 1 it can be seen that the percentage of the bee Fe-Ni phase decreases with increasing nickel fluence, as was the case when dose of Art was increased for ion beam mixing of Fe-Ni bilayers [4]. The hyperfine field distributions obtained in this study are similar to those obtained after ion beam mixing of Fe-Ni bilayers, from which a very narrow composition range (0.32 < x <: 0.34) was deduced 141. Otherwise, Fe,_,Ni, (0.32 < x < 0.39) alloy films obtained by simultaneous co-deposition of Ni and Fe and then annealed at 850 K exhibited rather similar P(H) distributions as in the present article (21. Then, from these comparisons. it is deduced that ion implan-
“Ni
implantatron
rn ‘%;e thin films
tation has produced Invar alloys (Fe, _.Ni, with x 0.35) whereas the maximum local concentration of nickel is never higher than 16 at.%. This could be explained by some short range diffusion processes leading to chemical clustering. Indeed, ion implantation in other systems often creates phases similar to those in the high temperature (700-~00 K) quenched alloys [14].
Acknowledgements The authors would like to express their thanks to Dr. C. Tosello (Trento) for providing samples and to Mr. A. Plantier for performing implantations. This work is a part of a research project financially supported by the Commission of the European Communities under contract SCI-00240C(A).
References PI K. Sumiyama. M. Kadono and Y. Nakamura. Trans. Jpn.
Inst. Met. 24 (1983) 190.
PI G. Dumpich. E. Becker, K. Schletz. W. Stamm. W. Keune, W. Kiauka and S. Murayama. J. Magn. Magn. Mater. 74 (1988) 237. [31 J. Arai. J. Appl. Phys. 64 (1988) 3143. [41 L.M. Gratton, A. Gupta. W. Keune. S. Lo Russo, .I. Parellada, G. Principi and C. Toseilo, Mater. Sci. Eng. A115 (1989) 161. [51 U. Comer, S. Nasu and W. Kappes. J. Magn. Magn. Mater. 10 (1979) 244. WI H. Ullrich and J. Hesse. J. Magn. Magn. Mater. 45 (1984) 315. I71 M. Shiga and Y. Nakamura, J. Magn. Magn. Mater. 40 (1984) 319. PI H. France and H.R. Rechenberg, J. Phys. FlS (1985) 719. 191 G. Le Caer and J.M. Dubois. J. Phys. El2 (1979) 1083. [lOI C.E. Johnson, MS. Ridout and T.E. Cranshaw. Proc. Phys. Sot. 81 (1963) 1079. 1111 B. Fultz and J.W. Morris Jr., Hyperfine Interactions 28 (1986) 553. 1121 H. Rechenberg, L. Billard, A. Chamberod and N. Natta, J. Phys. Chem. Solids 34 (1973) 1251. 1131 J.B. Mtiller and J. Hesse. Z. Phys. B54 (1983) 43. D4f H. Binczycka. B. Fornal, G. Marest. N. Moncoffre and J. Stanek. Radiat. Eff.. to be published.