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NM films (NM=Cu, Ta, Pd and Pt)
Journal of Magnetism and Magnetic Materials 226}230 (2001) 1640}1642
Ferromagnetic resonance linewidth for NM/80NiFe/NM "lms (NM"Cu, Ta, Pd and Pt) S. Mizukami*, Y. Ando, T. Miyazaki Departments of Applied Physics, Graduate School of Engineering, Tohoku University, Aoba-yama 08, Sendai, Miyagi 980-8579, Japan
Abstract The out-of-plane angular dependence of ferromagnetic resonance linewidth of non-magnetic metal (NM)/ 80NiFe(Py)(20}100 As )/NM (NM"Cu, Ta, Pd and Pt) sputtered "lms were measured for the investigation of magnetic damping. The linewidth for NM"Pd and Pt were larger than that of NM"Cu and Ta. Analysis of the angular dependence of the linewidth using Landau}Lifshitz}Gilbert equation with magnetic inhomogeneities showed that the Gilbert damping parameter, G, for NM"Pt and Pd were larger than the bulk value of Py and were dependent on the thickness of Py. G, for NM"Cu and Ta were same as the bulk value. These results show that the magnetization precession of Py layers sandwiched by Pt or Pd layers damps more rapidly. 2001 Elsevier Science B.V. All rights reserved. Keywords: Ferromagnetic resonance; Linewidth; Permalloy; Gilbert damping parameter
A number of investigations have been carried out on high-speed dynamics of magnetization from both fundamental and technological points of view [1]. Recent experiments revealed that the switching time of magnetization reversal shortened down to subnano-second [2]. In the high-speed region of magnetization dynamics like this, magnetic damping is an important factor. Therefore, it is important to investigate the fundamental magnetic damping of ferromagnets. Magnetic damping for thin or ultrathin "lms has been studied by several groups [3}8]. While, the mechanism of magnetic damping in metallic ferromagnetic thin "lm is not yet clearly understood. In this paper, ferromagnetic resonance (FMR) linewidth of 80NiFe (Py) thin "lms with various bu!er and capping layers were studied in order to investigate the magnetic damping in Py "lms. Non-magnetic metal (NM)/Py/NM (NM"Cu, Ta, Pd and Pt) "lms were fabricated by magnetron sputtering
* Corresponding author. Tel.: #81-22-217-7949; fax: #8122-217-7947. E-mail address: [email protected] (S. Mizukami).
on the substrate of corning 7059 glass. The base pressure was less than 5;10\ Torr and the deposition of "lms were performed in 7 mTorr of Ar. Thickness of the Py layer ranged from 20 to 100 As . The out-of-plane angular dependence of FMR were measured using an X-band (9.77 GHz) ESR spectrometer with a goniometer. Magnetization measurements were carried out by superconducting quantum interference devices (SQUID) magnetometer. The surface roughness of "lms were measured using an atomic force microscope (AFM). Fig. 1 shows the out-of-plane angular dependence of (a) resonance "eld (H ) and (b) linewidth (H ) of FMR 0 .. spectra for Pt(50 As )/Py(100 As )/Pt(50 As ) "lm and Cu(200 As )/ Py(100 As )/Cu(50 As ) "lm. is the polar angle between & DC magnetic "eld and the normal direction of a "lm. The out-of-plane angular dependence of H of both "lms 0 exhibits a peak at "03. There is no remarkable di!er& ence on the angular variations of H for both 0 "lms.However, H of the Pt/Py/Pt "lm is larger than .. that of Cu/Py/Cu "lm in all angles. In order to obtain the damping parameters from the angular variation of H , the analysis was performed .. using Landau}Lifshitz}Gilbert (LLG) equation. The effective demagnetization "eld, 4M , was only taken into account as an e!ective magnetic "eld. The formula
0304-8853/01/$ - see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 1 0 9 7 - 0
S. Mizukami et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 1640}1642
Fig. 1. Out-of-plane angular dependence of (a) resonance "eld (H ) and (b) linewidth (H ) for Cu(200 As )/Py(100 As )/Cu(50 As ) 0 .. "lm (open circle) and Pt(50 As )/Py(100 As )/Pt(50 As ) "lm (solid circle). Solid and broken lines are the calculation values.
of H and H were deduced by the general solution 0 .. described, for example, in Ref. [9]. Results of the calculation are also shown in Fig. 1 with solid and broken lines. The calculated values of H and 0 H agreed with the experimental data. Fitting para.. meters are g-factor and 4M for H and the damping 0 parameters, , for H . Using Gilbert damping para.. meter, G, is more appropriate because it is intrinsic for ferromagnet. G was estimated using the relation, G"M , where, M is saturation magnetization and 1 1 is gyromagnetic ratio. G was 2.7;10 s\ for Pt/ Py(100 As )/Pt "lm and 1.0;10 s\ for Cu/Py(100 As )/Cu "lm. Therefore, the broadening of linewidth for Pt/ Py(100 As )/Pt "lm is due to large intrinsic damping of magnetization precession. With decreasing Py thickness, the experimental H .. tended to deviate from the calculation values using LLG. In order to analyze H in thinner region of Py, the .. e!ects of two kinds of magnetic inhomogeneities in a "lm, which are the distribution of 4M and , were taken & into account in the analysis [10]. Details of the results of this analysis will be discussed elsewhere. Py thickness dependence of G with various NM are shown in Fig. 2. All NM bu!er and capping layers were 50 As thick. On decreasing the Py thickness, the values of G for NM"Pd and Pt increased up to 8.1;10 s\. While, the G values for NM"Cu and Ta are independent of the thickness of Py layers and are constant (0.9}1.0;10 s\), which is comparable to the bulk value (0.7;10 s\) [11]. This is also independent of the bu!er Cu and Ta layer thickness. According to the classical theory, the damping of magnetization precession can be caused by the spin}#ip scattering through spin}orbit coupling by phonon or defects in ferromagnetic metal [12]. For NM"Pd and Pt, the
1641
Fig. 2. Py thickness dependence of Gilbert damping parameters for NM/Py/NM with various NM. Both NM bu!er and capping layers are 50 As thick.
interface of Py layers can experience the strong spin}orbit coupling of Pt or Pd atoms. Therefore, it is very likely that the enhancements of G for NM"Pd and Pt are due to the strong spin}#ip scattering through the strong spin}orbit coupling at interfaces of Py layer. Increasing G with the concentration of Pt was also observed for Py Pt alloy thin "lm in our experi\6 6 ments. We calculated the thickness dependence of and M for Pt/Py/Pt "lms by regarding it as an exchange 1 coupled Py Pt /Py/Py Pt trilayers, using the ex\6 6 \6 6 perimental data of the Pt concentration dependence of and M for Py Pt "lms. The calculation does not 1 \6 6 match the experimental data for Pt/Py/Pt "lms. This result implies that we must consider not only the alloying e!ect but also some intrinsic interfacial e!ect for the origin of the large damping for NM"Pt. We would like to thank Prof. B. Heinrich for valuable discussion. This research was supported by the Storage Research Consortium, Regional Consortium Project (NEDO) and Grants-in-Aides for Scienti"c Research from the Ministry of Education, Science, Sports and Culture of Japan.
References [1] W.D. Doyle, S. Stinnett, C. Dawson, L. He, J. Magn. Soc. Jpn. 22 (1998) 91. [2] R.H. Koch, J.G. Deak, D.W. Abraham, P.L. Trouilloud, R.A. Altman, Yu Lu, W.J. Gallagher, R.E. Scheuerlein, K.P. Roche, S.S.P. Parkin, Phys. Rev. Lett. 81 (1998) 4512. [3] J.J. Krebs, F.J. Rachford, P. Lubitz, G.A. Prinz, J. Appl. Phys. 53 (1982) 8058. [4] B. Heinrich, K.B. Urquhart, A.S. Arrott, J.F. Cochran, K. Myrtle, S.T. Purcell, Phys. Rev. Lett. 59 (1987) 1756. [5] Z. Celinski, B. Heinrich, J. Appl. Phys. 70 (1991) 5935.
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S. Mizukami et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 1640}1642
[6] F. Schreiber, J. P#aum, Z. Frait, Th. MuK hge, J. Pelzl, Solid State Commun. 93 (1995) 965. [7] W. Platow, A.N. Anisimov, G.L. Dunifer, M. Farle, K. Barberschke, Phys. Rev. B 58 (1998) 5611. [8] R. Arias, D.L. Mills, Phys. Rev. B 60 (1999) 7395.
[9] H. Suhl, Phys. Rev. 97 (1955) 555. [10] C. Chappert, K. Le Dang, P. Beauvillain, H. Hurdequint, D. Renard, Phys. Rev. B 34 (1986) 3192. [11] D. Bastian, E. Biller, Phys. Stat. Sol. A 35 (1976) 113. [12] V. Kambersky, Can. J. Phys. 48 (1970) 2906.
Ferromagnetic resonance linewidth for NM/80NiFe/NM "lms (NM"Cu, Ta, Pd and Pt) S. Mizukami*, Y. Ando, T. Miyazaki Departments of Applied Physics, Graduate School of Engineering, Tohoku University, Aoba-yama 08, Sendai, Miyagi 980-8579, Japan
Abstract The out-of-plane angular dependence of ferromagnetic resonance linewidth of non-magnetic metal (NM)/ 80NiFe(Py)(20}100 As )/NM (NM"Cu, Ta, Pd and Pt) sputtered "lms were measured for the investigation of magnetic damping. The linewidth for NM"Pd and Pt were larger than that of NM"Cu and Ta. Analysis of the angular dependence of the linewidth using Landau}Lifshitz}Gilbert equation with magnetic inhomogeneities showed that the Gilbert damping parameter, G, for NM"Pt and Pd were larger than the bulk value of Py and were dependent on the thickness of Py. G, for NM"Cu and Ta were same as the bulk value. These results show that the magnetization precession of Py layers sandwiched by Pt or Pd layers damps more rapidly. 2001 Elsevier Science B.V. All rights reserved. Keywords: Ferromagnetic resonance; Linewidth; Permalloy; Gilbert damping parameter
A number of investigations have been carried out on high-speed dynamics of magnetization from both fundamental and technological points of view [1]. Recent experiments revealed that the switching time of magnetization reversal shortened down to subnano-second [2]. In the high-speed region of magnetization dynamics like this, magnetic damping is an important factor. Therefore, it is important to investigate the fundamental magnetic damping of ferromagnets. Magnetic damping for thin or ultrathin "lms has been studied by several groups [3}8]. While, the mechanism of magnetic damping in metallic ferromagnetic thin "lm is not yet clearly understood. In this paper, ferromagnetic resonance (FMR) linewidth of 80NiFe (Py) thin "lms with various bu!er and capping layers were studied in order to investigate the magnetic damping in Py "lms. Non-magnetic metal (NM)/Py/NM (NM"Cu, Ta, Pd and Pt) "lms were fabricated by magnetron sputtering
* Corresponding author. Tel.: #81-22-217-7949; fax: #8122-217-7947. E-mail address: [email protected] (S. Mizukami).
on the substrate of corning 7059 glass. The base pressure was less than 5;10\ Torr and the deposition of "lms were performed in 7 mTorr of Ar. Thickness of the Py layer ranged from 20 to 100 As . The out-of-plane angular dependence of FMR were measured using an X-band (9.77 GHz) ESR spectrometer with a goniometer. Magnetization measurements were carried out by superconducting quantum interference devices (SQUID) magnetometer. The surface roughness of "lms were measured using an atomic force microscope (AFM). Fig. 1 shows the out-of-plane angular dependence of (a) resonance "eld (H ) and (b) linewidth (H ) of FMR 0 .. spectra for Pt(50 As )/Py(100 As )/Pt(50 As ) "lm and Cu(200 As )/ Py(100 As )/Cu(50 As ) "lm. is the polar angle between & DC magnetic "eld and the normal direction of a "lm. The out-of-plane angular dependence of H of both "lms 0 exhibits a peak at "03. There is no remarkable di!er& ence on the angular variations of H for both 0 "lms.However, H of the Pt/Py/Pt "lm is larger than .. that of Cu/Py/Cu "lm in all angles. In order to obtain the damping parameters from the angular variation of H , the analysis was performed .. using Landau}Lifshitz}Gilbert (LLG) equation. The effective demagnetization "eld, 4M , was only taken into account as an e!ective magnetic "eld. The formula
0304-8853/01/$ - see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 1 0 9 7 - 0
S. Mizukami et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 1640}1642
Fig. 1. Out-of-plane angular dependence of (a) resonance "eld (H ) and (b) linewidth (H ) for Cu(200 As )/Py(100 As )/Cu(50 As ) 0 .. "lm (open circle) and Pt(50 As )/Py(100 As )/Pt(50 As ) "lm (solid circle). Solid and broken lines are the calculation values.
of H and H were deduced by the general solution 0 .. described, for example, in Ref. [9]. Results of the calculation are also shown in Fig. 1 with solid and broken lines. The calculated values of H and 0 H agreed with the experimental data. Fitting para.. meters are g-factor and 4M for H and the damping 0 parameters, , for H . Using Gilbert damping para.. meter, G, is more appropriate because it is intrinsic for ferromagnet. G was estimated using the relation, G"M , where, M is saturation magnetization and 1 1 is gyromagnetic ratio. G was 2.7;10 s\ for Pt/ Py(100 As )/Pt "lm and 1.0;10 s\ for Cu/Py(100 As )/Cu "lm. Therefore, the broadening of linewidth for Pt/ Py(100 As )/Pt "lm is due to large intrinsic damping of magnetization precession. With decreasing Py thickness, the experimental H .. tended to deviate from the calculation values using LLG. In order to analyze H in thinner region of Py, the .. e!ects of two kinds of magnetic inhomogeneities in a "lm, which are the distribution of 4M and , were taken & into account in the analysis [10]. Details of the results of this analysis will be discussed elsewhere. Py thickness dependence of G with various NM are shown in Fig. 2. All NM bu!er and capping layers were 50 As thick. On decreasing the Py thickness, the values of G for NM"Pd and Pt increased up to 8.1;10 s\. While, the G values for NM"Cu and Ta are independent of the thickness of Py layers and are constant (0.9}1.0;10 s\), which is comparable to the bulk value (0.7;10 s\) [11]. This is also independent of the bu!er Cu and Ta layer thickness. According to the classical theory, the damping of magnetization precession can be caused by the spin}#ip scattering through spin}orbit coupling by phonon or defects in ferromagnetic metal [12]. For NM"Pd and Pt, the
1641
Fig. 2. Py thickness dependence of Gilbert damping parameters for NM/Py/NM with various NM. Both NM bu!er and capping layers are 50 As thick.
interface of Py layers can experience the strong spin}orbit coupling of Pt or Pd atoms. Therefore, it is very likely that the enhancements of G for NM"Pd and Pt are due to the strong spin}#ip scattering through the strong spin}orbit coupling at interfaces of Py layer. Increasing G with the concentration of Pt was also observed for Py Pt alloy thin "lm in our experi\6 6 ments. We calculated the thickness dependence of and M for Pt/Py/Pt "lms by regarding it as an exchange 1 coupled Py Pt /Py/Py Pt trilayers, using the ex\6 6 \6 6 perimental data of the Pt concentration dependence of and M for Py Pt "lms. The calculation does not 1 \6 6 match the experimental data for Pt/Py/Pt "lms. This result implies that we must consider not only the alloying e!ect but also some intrinsic interfacial e!ect for the origin of the large damping for NM"Pt. We would like to thank Prof. B. Heinrich for valuable discussion. This research was supported by the Storage Research Consortium, Regional Consortium Project (NEDO) and Grants-in-Aides for Scienti"c Research from the Ministry of Education, Science, Sports and Culture of Japan.
References [1] W.D. Doyle, S. Stinnett, C. Dawson, L. He, J. Magn. Soc. Jpn. 22 (1998) 91. [2] R.H. Koch, J.G. Deak, D.W. Abraham, P.L. Trouilloud, R.A. Altman, Yu Lu, W.J. Gallagher, R.E. Scheuerlein, K.P. Roche, S.S.P. Parkin, Phys. Rev. Lett. 81 (1998) 4512. [3] J.J. Krebs, F.J. Rachford, P. Lubitz, G.A. Prinz, J. Appl. Phys. 53 (1982) 8058. [4] B. Heinrich, K.B. Urquhart, A.S. Arrott, J.F. Cochran, K. Myrtle, S.T. Purcell, Phys. Rev. Lett. 59 (1987) 1756. [5] Z. Celinski, B. Heinrich, J. Appl. Phys. 70 (1991) 5935.
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S. Mizukami et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 1640}1642
[6] F. Schreiber, J. P#aum, Z. Frait, Th. MuK hge, J. Pelzl, Solid State Commun. 93 (1995) 965. [7] W. Platow, A.N. Anisimov, G.L. Dunifer, M. Farle, K. Barberschke, Phys. Rev. B 58 (1998) 5611. [8] R. Arias, D.L. Mills, Phys. Rev. B 60 (1999) 7395.
[9] H. Suhl, Phys. Rev. 97 (1955) 555. [10] C. Chappert, K. Le Dang, P. Beauvillain, H. Hurdequint, D. Renard, Phys. Rev. B 34 (1986) 3192. [11] D. Bastian, E. Biller, Phys. Stat. Sol. A 35 (1976) 113. [12] V. Kambersky, Can. J. Phys. 48 (1970) 2906.