- Email: [email protected]
FeB trilayers deposited onto bowed substrates
Journal of Magnetism and Magnetic Materials 215}216 (2000) 566}569
Uniaxial magnetic properties of sputtered FeB/Cu/FeB trilayers deposited onto bowed substrates T. Stobiecki *, J. Wrona , M. Czapkiewicz , C. Prados, F.J. Castan o, D. Garcia, M. VaH zquez, M. Kopcewicz, A. Grabias, R. Z uberek Department of Electronics, University of Mining and Metallurgy, al. Mickiewicza 30, 30-059 Krako& w, Poland Instituto de Magnetismo Aplicado, RENFE-UCM, P.O. Box 155, 28230 Las Rozas, Madrid, Spain ITME, ul. Wo& lczyn& ska 133, 01-919 Warsaw, Poland Institute of Physics PAS, al. Lotniko& w 32/46, 02-668 Warsaw, Poland
Abstract Fe B /Cu/Fe B trilayers were deposited onto bowed glass substrates using the RF sputtering technique. On removing the trilayers system from the sputtering chamber, a magnetoelastic uniaxial in-plane anisotropy was induced due to the compressive stress developed when the substrates recovered their initial shape. For the "rst type of the sample the permanent stress was applied in both FeB bottom and top layer in the same directions (parallel to the longer axis of the glass slide). For the second type of the sample the stress was applied for the bottom FeB layer under #213 and top layer under !213 angle (with respect to the longer axis of the glass slide). It was found, using Kerr magnetometry, that due to the positive magnetostriction nature of the FeB layers the directions of the easy axis have been induced separately in each FeB sublayer. The magnetic and magnetoelastic properties of these samples are discussed. 2000 Elsevier Science B.V. All rights reserved. Keywords: Magnetoelastic uniaxial in-plane anisotropy; Amorphous multilayers.
Magnetoelastic coupling provides the possibility of inducing uniaxial magnetic anisotropy (UMA) in thin multilayers structures by an externally applied stress [1]. The Spanish group of authors of this paper has recently reported a new experimental technique of inducing UMA in bilayers structures by means of bowing substrate prior to the deposition [2,3]. The aim of this study is to investigate the e!ect of an applied stress on the mechanism of inducing uniaxial anisotropy in the amorphous ferromagnetic layers (Fe B ) separated by a non-mag netic (Cu) spacer. Fe B (500 As )/Cu(40 As )/Fe B (500 As ) trilayers were deposited onto bowed glass substrates (50;22; 0.15 mm) using the RF sputtering technique. A 20 As thick Cu coating layer was deposited to prevent oxidation.
* Corresponding author.Tel.: #4812-617-2596; fax: #4812617-3550. E-mail address: [email protected] (T. Stobiecki).
Prior to the deposition the substrates were bowed by means of two clamps attached in the sputtering chamber whose distance was accurately controlled using three micrometric threaded rods (for details see in Ref. [3]). This bowing produces a positive strain of around 3.5;10\ at the glass surface where the "lms were deposited. When the deposition was completed the samples were released from the clamps and thus recovered their initial planar shape, developing a permanent compressive stress. Trilayers with two di!erent directions of the applied bowing of the substrates were analysed. The permanent stress was applied to the sample named as ang.0 along the longer axis of the slide during the complete deposition sequence. Bowing of the sample named as ang.21 was "rst applied at the angle #213 with respect to the longer axis of the slide then the "rst FeB and the Cu layers were deposited. When this was completed, the chamber was opened and the bowing direction was changed to the angle !213 with respect to the longer axis of the slide. In these conditions the second FeB and
0304-8853/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 2 2 3 - 7
T. Stobiecki et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 566}569
the capping Cu layers were deposited. Due to the positive magnetostriction of the target material Fe B (j "30;10\) of the FeB magnetic layers, an easy 1 magnetisation axis transverse to the compression axis was developed. From the centre of the sample two pieces were cut: one for the structure characterisation (20;20 mm) and second one for determining the magnetic properties (4;10 mm). The structure of the discussed samples was controlled by conversion electrons moK ssbauer spectroscopy (CEMS) and the X-ray of small and high angle di!raction. The CEMS spectra of FeB/Cu/FeB systems of ang.0 and ang.21 (which do not show any signi"cant di!erences between each other) consist of a broadened sextet due to magnetic hyper"ne "eld distribution (B ), characteristic of the amorphous Fe B . The average hyper"ne "eld is about 24.8 and 24 T and the widths of P(B ) distributions are 7.07 and 6.04 T for ang.0 and ang.21, respectively. The
567
results indicate strong in-plane spin alignment in both "lms. The D parameter (de"ned as the line intensity ratio of the second line of the sextet with respect to the third line) is about 3.6 and 3.7 for ang.0 and ang.21, respectively. However, information regarding the di!erences in the in-plane anisotropy cannot be obtained from the conventional CEMS measurements. From X-ray re#ectivity analysis a well-de"ned layered structure was con"rmed, however, h}2h scan (high angle range) shows characteristic amorphous pattern for Fe B without traces of the crystalline phase of the Cu spacer. The magnetization reversal process was analysed on the basis of the measurements at room temperature of the hysteresis loops obtained: by the resonance vibrating sample magnetometer (R-VSM) [4], magneto-optical Kerr e!ect (MOKE) and magnetoresistance e!ect by DC-current with four contacts method. Fig. 1 (a}d) shows the MOKE hysteresis loops measured in the easy
Fig. 1. The MOKE hysteresis loops in easy- and hard-axis direction taken in the three di!erent places of the samples ang.0 and ang.21: (a) ang.0 FSS: the range of change of the uniaxial anisotropy "eld (H ) is 5117(H (5260 (A/m) and the range of change of the coercivity "eld (H ) is 732(H (792 (A/m), (b) ang.0 SS: 5969(H (7082 (A/m); 601(H (637 (A/m), (c) ang.21 FSS: 4178(H (4703 (A/m); 935(H (983 (A/m), (d) ang.21 SS: 4210(H (4520 (A/m); 955(H (1007 (A/m). Inside schematic representation of the applied stress direction (bold arrows) and easy- and hard-axis directions (thin arrows).
568
T. Stobiecki et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 566}569
Fig. 2. The R-VSM hysteresis loops in easy- and hard-axis direction of the sample: (a) ang.0: H "5809 (A/m); H "752 (A/m), (b) ang.21: H "4027 (A/m); H "780 (A/m). Table 1 The magnetic and magnetoelastic data of the sample ang.0 and ang.21
Fig. 3. The AMR curve of the sample ang.0 taken in the hardaxis direction (*R/R"0.24%). Points: experimental results, line: "tted with H "5809 (A/m) to the relation given in the text.
and hard direction in three di!erent places of the sample on the "lm surface side (FSS) and substrate side (SS), for ang.0 and ang.21, respectively. Due to the limited penetration depth of the laser beam (&200 As ) it was possible to obtain the hysteresis loop for each individual FeB layer on the bottom and the top. The MOKE hysteresis loops are rectangular in the direction of the easy axis and close and linear in the hard axis direction in both samples. R-VSM hysteresis loops, which give averaged information (detected from the total volume of the sample), are in the case of ang.0 (Fig. 2a) the same as MOKE hysteresis loops, while R-VSM loop in the hard axis
Samples
k M (T)
j 10\
K (kJ/m)
p (10 Pa)
ang.0 ang.21
1.79 1.73
29 22
5.24 3.77
1.2 1.14
direction of ang.21 (Fig. 2b) is open due to the resultant anisotropy of the trilayers system FeB(#213)/Cu/ FeB(!213). The uniaxial anisotropy e!ect of the sample ang.0 was con"rmed by anisotropic magnetoresistance (AMR) curve measured in the hard axis direction. According to the model of the coherent rotation of magnetization the dependence R(H)"R #(R !R ) , , , ;[1!(H/H )] is parabolic [5] (see Fig. 3). The com pressive stresses (p), which are induced through the magnetostrictive coupling of the uniaxial anisotropy, were estimated from the formula K "! j p [1]. The satu 1 ration magnetostriction (j ) was determined using the 1 method of strain-modulated ferromagnetic resonance [6]. In Table 1, the magnetic and magnetoelastic data for the samples ang.0 and ang.21 are collected. Summarizing, we have shown that the uniaxial in-plane anisotropies can be induced separately in each individual amorphous, magnetostrictive Fe B sublayer of the sys tem Fe B (500 As )/Cu(40 As )/Fe B (500 As ) in arbitrary direction of developed compressive stresses, obtained due to the sputtering deposition onto the bowed substrate. This work was partially supported by the Grant 8T11B 012 16 and MAT 98-0965. Participation in the SMM14 Conference was made possible by the Grant UMM 11-11-120-68.
T. Stobiecki et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 566}569
References [1] K. Saito, IEEE Trans. Magn. 26 (1990) 2942. [2] D. Garcia, F.J. Castan o, C. Prado, M. VaH zquez, F. Castan o, Appl. Phys. Lett. 74 (1999) 105. [3] D. Garcia, J.L. Mun oz, F.J. Castan o, C. Prados, A. Asenjo, J.M. Garcia, M. Vazquez, J. Appl. Phys. 85 (1999) 4809.
569
[4] J. Wrona, M. Czapkiewicz, T. Stobiecki, J. Magn. Magn. Mater. 196}197 (1999) 935. [5] T. Stobiecki, A. Paja, Acta Phys. Polon. A 41 (1972) 344. [6] R. Z uberek, H. Szymczak, D. Z ymierska, G. Suran, M. Naili, J. Magn. Magn. Mater. 104}107 (1992) 117.
Uniaxial magnetic properties of sputtered FeB/Cu/FeB trilayers deposited onto bowed substrates T. Stobiecki *, J. Wrona , M. Czapkiewicz , C. Prados, F.J. Castan o, D. Garcia, M. VaH zquez, M. Kopcewicz, A. Grabias, R. Z uberek Department of Electronics, University of Mining and Metallurgy, al. Mickiewicza 30, 30-059 Krako& w, Poland Instituto de Magnetismo Aplicado, RENFE-UCM, P.O. Box 155, 28230 Las Rozas, Madrid, Spain ITME, ul. Wo& lczyn& ska 133, 01-919 Warsaw, Poland Institute of Physics PAS, al. Lotniko& w 32/46, 02-668 Warsaw, Poland
Abstract Fe B /Cu/Fe B trilayers were deposited onto bowed glass substrates using the RF sputtering technique. On removing the trilayers system from the sputtering chamber, a magnetoelastic uniaxial in-plane anisotropy was induced due to the compressive stress developed when the substrates recovered their initial shape. For the "rst type of the sample the permanent stress was applied in both FeB bottom and top layer in the same directions (parallel to the longer axis of the glass slide). For the second type of the sample the stress was applied for the bottom FeB layer under #213 and top layer under !213 angle (with respect to the longer axis of the glass slide). It was found, using Kerr magnetometry, that due to the positive magnetostriction nature of the FeB layers the directions of the easy axis have been induced separately in each FeB sublayer. The magnetic and magnetoelastic properties of these samples are discussed. 2000 Elsevier Science B.V. All rights reserved. Keywords: Magnetoelastic uniaxial in-plane anisotropy; Amorphous multilayers.
Magnetoelastic coupling provides the possibility of inducing uniaxial magnetic anisotropy (UMA) in thin multilayers structures by an externally applied stress [1]. The Spanish group of authors of this paper has recently reported a new experimental technique of inducing UMA in bilayers structures by means of bowing substrate prior to the deposition [2,3]. The aim of this study is to investigate the e!ect of an applied stress on the mechanism of inducing uniaxial anisotropy in the amorphous ferromagnetic layers (Fe B ) separated by a non-mag netic (Cu) spacer. Fe B (500 As )/Cu(40 As )/Fe B (500 As ) trilayers were deposited onto bowed glass substrates (50;22; 0.15 mm) using the RF sputtering technique. A 20 As thick Cu coating layer was deposited to prevent oxidation.
* Corresponding author.Tel.: #4812-617-2596; fax: #4812617-3550. E-mail address: [email protected] (T. Stobiecki).
Prior to the deposition the substrates were bowed by means of two clamps attached in the sputtering chamber whose distance was accurately controlled using three micrometric threaded rods (for details see in Ref. [3]). This bowing produces a positive strain of around 3.5;10\ at the glass surface where the "lms were deposited. When the deposition was completed the samples were released from the clamps and thus recovered their initial planar shape, developing a permanent compressive stress. Trilayers with two di!erent directions of the applied bowing of the substrates were analysed. The permanent stress was applied to the sample named as ang.0 along the longer axis of the slide during the complete deposition sequence. Bowing of the sample named as ang.21 was "rst applied at the angle #213 with respect to the longer axis of the slide then the "rst FeB and the Cu layers were deposited. When this was completed, the chamber was opened and the bowing direction was changed to the angle !213 with respect to the longer axis of the slide. In these conditions the second FeB and
0304-8853/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 2 2 3 - 7
T. Stobiecki et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 566}569
the capping Cu layers were deposited. Due to the positive magnetostriction of the target material Fe B (j "30;10\) of the FeB magnetic layers, an easy 1 magnetisation axis transverse to the compression axis was developed. From the centre of the sample two pieces were cut: one for the structure characterisation (20;20 mm) and second one for determining the magnetic properties (4;10 mm). The structure of the discussed samples was controlled by conversion electrons moK ssbauer spectroscopy (CEMS) and the X-ray of small and high angle di!raction. The CEMS spectra of FeB/Cu/FeB systems of ang.0 and ang.21 (which do not show any signi"cant di!erences between each other) consist of a broadened sextet due to magnetic hyper"ne "eld distribution (B ), characteristic of the amorphous Fe B . The average hyper"ne "eld is about 24.8 and 24 T and the widths of P(B ) distributions are 7.07 and 6.04 T for ang.0 and ang.21, respectively. The
567
results indicate strong in-plane spin alignment in both "lms. The D parameter (de"ned as the line intensity ratio of the second line of the sextet with respect to the third line) is about 3.6 and 3.7 for ang.0 and ang.21, respectively. However, information regarding the di!erences in the in-plane anisotropy cannot be obtained from the conventional CEMS measurements. From X-ray re#ectivity analysis a well-de"ned layered structure was con"rmed, however, h}2h scan (high angle range) shows characteristic amorphous pattern for Fe B without traces of the crystalline phase of the Cu spacer. The magnetization reversal process was analysed on the basis of the measurements at room temperature of the hysteresis loops obtained: by the resonance vibrating sample magnetometer (R-VSM) [4], magneto-optical Kerr e!ect (MOKE) and magnetoresistance e!ect by DC-current with four contacts method. Fig. 1 (a}d) shows the MOKE hysteresis loops measured in the easy
Fig. 1. The MOKE hysteresis loops in easy- and hard-axis direction taken in the three di!erent places of the samples ang.0 and ang.21: (a) ang.0 FSS: the range of change of the uniaxial anisotropy "eld (H ) is 5117(H (5260 (A/m) and the range of change of the coercivity "eld (H ) is 732(H (792 (A/m), (b) ang.0 SS: 5969(H (7082 (A/m); 601(H (637 (A/m), (c) ang.21 FSS: 4178(H (4703 (A/m); 935(H (983 (A/m), (d) ang.21 SS: 4210(H (4520 (A/m); 955(H (1007 (A/m). Inside schematic representation of the applied stress direction (bold arrows) and easy- and hard-axis directions (thin arrows).
568
T. Stobiecki et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 566}569
Fig. 2. The R-VSM hysteresis loops in easy- and hard-axis direction of the sample: (a) ang.0: H "5809 (A/m); H "752 (A/m), (b) ang.21: H "4027 (A/m); H "780 (A/m). Table 1 The magnetic and magnetoelastic data of the sample ang.0 and ang.21
Fig. 3. The AMR curve of the sample ang.0 taken in the hardaxis direction (*R/R"0.24%). Points: experimental results, line: "tted with H "5809 (A/m) to the relation given in the text.
and hard direction in three di!erent places of the sample on the "lm surface side (FSS) and substrate side (SS), for ang.0 and ang.21, respectively. Due to the limited penetration depth of the laser beam (&200 As ) it was possible to obtain the hysteresis loop for each individual FeB layer on the bottom and the top. The MOKE hysteresis loops are rectangular in the direction of the easy axis and close and linear in the hard axis direction in both samples. R-VSM hysteresis loops, which give averaged information (detected from the total volume of the sample), are in the case of ang.0 (Fig. 2a) the same as MOKE hysteresis loops, while R-VSM loop in the hard axis
Samples
k M (T)
j 10\
K (kJ/m)
p (10 Pa)
ang.0 ang.21
1.79 1.73
29 22
5.24 3.77
1.2 1.14
direction of ang.21 (Fig. 2b) is open due to the resultant anisotropy of the trilayers system FeB(#213)/Cu/ FeB(!213). The uniaxial anisotropy e!ect of the sample ang.0 was con"rmed by anisotropic magnetoresistance (AMR) curve measured in the hard axis direction. According to the model of the coherent rotation of magnetization the dependence R(H)"R #(R !R ) , , , ;[1!(H/H )] is parabolic [5] (see Fig. 3). The com pressive stresses (p), which are induced through the magnetostrictive coupling of the uniaxial anisotropy, were estimated from the formula K "! j p [1]. The satu 1 ration magnetostriction (j ) was determined using the 1 method of strain-modulated ferromagnetic resonance [6]. In Table 1, the magnetic and magnetoelastic data for the samples ang.0 and ang.21 are collected. Summarizing, we have shown that the uniaxial in-plane anisotropies can be induced separately in each individual amorphous, magnetostrictive Fe B sublayer of the sys tem Fe B (500 As )/Cu(40 As )/Fe B (500 As ) in arbitrary direction of developed compressive stresses, obtained due to the sputtering deposition onto the bowed substrate. This work was partially supported by the Grant 8T11B 012 16 and MAT 98-0965. Participation in the SMM14 Conference was made possible by the Grant UMM 11-11-120-68.
T. Stobiecki et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 566}569
References [1] K. Saito, IEEE Trans. Magn. 26 (1990) 2942. [2] D. Garcia, F.J. Castan o, C. Prado, M. VaH zquez, F. Castan o, Appl. Phys. Lett. 74 (1999) 105. [3] D. Garcia, J.L. Mun oz, F.J. Castan o, C. Prados, A. Asenjo, J.M. Garcia, M. Vazquez, J. Appl. Phys. 85 (1999) 4809.
569
[4] J. Wrona, M. Czapkiewicz, T. Stobiecki, J. Magn. Magn. Mater. 196}197 (1999) 935. [5] T. Stobiecki, A. Paja, Acta Phys. Polon. A 41 (1972) 344. [6] R. Z uberek, H. Szymczak, D. Z ymierska, G. Suran, M. Naili, J. Magn. Magn. Mater. 104}107 (1992) 117.