3d金属超薄膜的结构和磁性研究
摘要
近十几年以来，薄膜磁学的研究得到了迅速的壮大。在实验上随着样品制
备水平和表征技术的迅速发展，使得人们能够对二维、一维甚至零维体系的磁
学性质进行研究，取得了很多激动人心的进展。在理论方面，随着计算方法和
计算能力的惊人发展，从第一性原理出发对薄膜体系的磁学性质的预言能力得
到了巨大的提高。磁性金属薄膜的研究不仅有助于深入了解低维金属磁性的本
质，而且为自旋电子学的发展提供了物理基础。本论文针对金属Cr在GaAs(001)
表面的外延结构和机理，超薄fcc Fe/Cu(100) 体系的磁性，金属Ni的体心立方
结构的磁学性质，用激光分子束外延制备的Co/Pd(100) 界面的磁学性质等问题
展开了一些研究，得到了以下结果。
1． 研究了金属Cr薄膜在GaAs(001) 表面外延生长的结构和机理。结果表
明，Cr外延生长的结构和生长温度密切相关。在生长过程中存在两种模式的竞
争。当生长温度低于70℃的时候，Cr以bcc(211) 面平行外延在GaAs(001) 面上，
当生长温度超过130℃的时候，Cr以bcc(001) 面平行外延在GaAs(001) 面上。
当生长温度处于上述两者之间时，两种外延模式同时存在。Cr与GaAs界面的
状况对于生长起到了重要的作用。
2． 研究了超薄fcc Fe/Cu(001) 体系的结构不稳定性以及它的磁学性质。发现
对于厚度在6-9原子单层(ML)的fcc Fe薄膜，它具有一种类似于自旋密度波形
式的磁性结构。对于室温下生长的fcc Fe薄膜，当厚度超过9ML时，整个薄膜
对温度具有不稳定性，降温能够导致薄膜发生fcc到bcc结构的马氏相变。
3． 在170K的生长温度下，通过分子束外延在GaAs(001) 表面生长得到体心
立方结构金属Ni薄膜。利用同步辐射x射线掠角衍射，同步辐射光电子谱，磁
光Kerr效应，铁磁共振，超导量子干涉器件等对bcc Ni/GaAs(001) 上的晶格常
数，磁矩，面内各向异性，垂直膜面方向上的能带结构进行了研究，并和fcc Ni
进行了对比。
4． 研究了用激光分子束外延方式制备的Co/Pd(100) 界面的磁学性质，和用
热蒸发方式外延制备的Co/Pd(100) 界面进行了对比。结果表明，用激光分子束
外延的方式能够很大程度的改变界面的状况，整个界面的磁学性质发生了巨大
的改变，在Co厚度小于1ML时，体系总磁光信号远大于用热蒸发方式制备的
Co薄膜。当外延的Co薄膜厚度超过1ML时在界面上会形成了特殊的界面合
金，极大的降低了系统的总磁光信号。超过1． 4ML后，总磁光信号又重新开始
随厚度的增加而线性增加。用原位的磁光椭偏仪证实反常的磁性信号变化确实
来源于磁光的贡献，并不是折射率变化引起。
With the development of the experiment technology and theory, the research of the ultrathin magnetic films has made much progress in last decade. Lots of manufactured structure such as two-dimensional film, one-dimensional line and zero-dimensional dot has attracted more and more attentions. The deeply understand of the properties of low dimensional magnetic structures is useful both to the fundamental physics and to the new progress of commercially application in spintronics. In this thesis, I mainly introduce my recent work about the structure of Cr films growth on GaAs(001) surface, the spin density wave of fee Fe on Cu(100), magnetism of bcc Ni on GaAs(001), interface magnetism of Co/Pd(100) epitaxied by Pulse Laser Deposition.
1. Growth of Cr thin films on GaAs(001) was carried out using Molecular Beam Epitaxy and was investigated by in situ reflection high-energy electron diffraction (RHEED) and ex situ X-ray diffraction (XRD). The results show that there are two competing mechanisms during the growth, and the film structure strongly depends on the growth temperature. The single-crystalline Cr films with the body-centered-cubic (bcc) structure are obtained, with the epitaxial relationship of (0 0 1)[0 0 l]||Cr(0 0 1)[001] GaAs and (001)[100]Cr(001)[100]GaAs .
2. For Fe films epitaxially grown on Cu(100) at 300 K, the total magnetic moment as a function of film thickness and its temperature dependence have been investigated in situ with a multi-technique approach. The results exclude the collinear type-1 antiferromagnetic configuration as the magnetic structure for face-centered cubic (fee) Fe films on Cu(lOO). It is proposed that a spin-density-wave (SDW) state is responsible for the magnetic structure. Based on the accurate thickness calibration, the borderlines of the three well-known regions with distinct magnetic properties are determined unambiguously for Fe films on Cu(100). A theoretically predicted temperature driven martensitic phase transition between regions II and III is indeed confirmed in experiment.
3. The single-crystalline Ni film with the body-centered-cubic(bcc) structure are obtained epitaxially on GaAs(001) surface at 170K. The in-plane and out-of-plane lattice constant of Ni/GaAs(100) was determined X-ray diffraction. And the magnetic properties and electron structure of bcc Ni have been studied with MOKE, FMR, SQUID, and Angle Resolved Photoemission.
4 Ultrathin Co films epitaxially grown on Pd(100) by Pulse Laser Deposition(PLD) and by normal Thermal Deposition(TD) was investigated respectively by in situ MOKE and Optical Ellipticmeter. The result demonstrates that the magnetic property strongly depends on interface condition. Magnetic-optical Kerr signal decreases abnormally in the PLD Co/Pd when Co is thicker than about
1ML. The total magnetic signal reach the minimum at about 1.3~1.4ML and then again increased linearly with the increasing of Co film thickness.
备水平和表征技术的迅速发展，使得人们能够对二维、一维甚至零维体系的磁
学性质进行研究，取得了很多激动人心的进展。在理论方面，随着计算方法和
计算能力的惊人发展，从第一性原理出发对薄膜体系的磁学性质的预言能力得
到了巨大的提高。磁性金属薄膜的研究不仅有助于深入了解低维金属磁性的本
质，而且为自旋电子学的发展提供了物理基础。本论文针对金属Cr在GaAs(001)
表面的外延结构和机理，超薄fcc Fe/Cu(100) 体系的磁性，金属Ni的体心立方
结构的磁学性质，用激光分子束外延制备的Co/Pd(100) 界面的磁学性质等问题
展开了一些研究，得到了以下结果。
1． 研究了金属Cr薄膜在GaAs(001) 表面外延生长的结构和机理。结果表
明，Cr外延生长的结构和生长温度密切相关。在生长过程中存在两种模式的竞
争。当生长温度低于70℃的时候，Cr以bcc(211) 面平行外延在GaAs(001) 面上，
当生长温度超过130℃的时候，Cr以bcc(001) 面平行外延在GaAs(001) 面上。
当生长温度处于上述两者之间时，两种外延模式同时存在。Cr与GaAs界面的
状况对于生长起到了重要的作用。
2． 研究了超薄fcc Fe/Cu(001) 体系的结构不稳定性以及它的磁学性质。发现
对于厚度在6-9原子单层(ML)的fcc Fe薄膜，它具有一种类似于自旋密度波形
式的磁性结构。对于室温下生长的fcc Fe薄膜，当厚度超过9ML时，整个薄膜
对温度具有不稳定性，降温能够导致薄膜发生fcc到bcc结构的马氏相变。
3． 在170K的生长温度下，通过分子束外延在GaAs(001) 表面生长得到体心
立方结构金属Ni薄膜。利用同步辐射x射线掠角衍射，同步辐射光电子谱，磁
光Kerr效应，铁磁共振，超导量子干涉器件等对bcc Ni/GaAs(001) 上的晶格常
数，磁矩，面内各向异性，垂直膜面方向上的能带结构进行了研究，并和fcc Ni
进行了对比。
4． 研究了用激光分子束外延方式制备的Co/Pd(100) 界面的磁学性质，和用
热蒸发方式外延制备的Co/Pd(100) 界面进行了对比。结果表明，用激光分子束
外延的方式能够很大程度的改变界面的状况，整个界面的磁学性质发生了巨大
的改变，在Co厚度小于1ML时，体系总磁光信号远大于用热蒸发方式制备的
Co薄膜。当外延的Co薄膜厚度超过1ML时在界面上会形成了特殊的界面合
金，极大的降低了系统的总磁光信号。超过1． 4ML后，总磁光信号又重新开始
随厚度的增加而线性增加。用原位的磁光椭偏仪证实反常的磁性信号变化确实
来源于磁光的贡献，并不是折射率变化引起。
With the development of the experiment technology and theory, the research of the ultrathin magnetic films has made much progress in last decade. Lots of manufactured structure such as two-dimensional film, one-dimensional line and zero-dimensional dot has attracted more and more attentions. The deeply understand of the properties of low dimensional magnetic structures is useful both to the fundamental physics and to the new progress of commercially application in spintronics. In this thesis, I mainly introduce my recent work about the structure of Cr films growth on GaAs(001) surface, the spin density wave of fee Fe on Cu(100), magnetism of bcc Ni on GaAs(001), interface magnetism of Co/Pd(100) epitaxied by Pulse Laser Deposition.
1. Growth of Cr thin films on GaAs(001) was carried out using Molecular Beam Epitaxy and was investigated by in situ reflection high-energy electron diffraction (RHEED) and ex situ X-ray diffraction (XRD). The results show that there are two competing mechanisms during the growth, and the film structure strongly depends on the growth temperature. The single-crystalline Cr films with the body-centered-cubic (bcc) structure are obtained, with the epitaxial relationship of (0 0 1)[0 0 l]||Cr(0 0 1)[001] GaAs and (001)[100]Cr(001)[100]GaAs .
2. For Fe films epitaxially grown on Cu(100) at 300 K, the total magnetic moment as a function of film thickness and its temperature dependence have been investigated in situ with a multi-technique approach. The results exclude the collinear type-1 antiferromagnetic configuration as the magnetic structure for face-centered cubic (fee) Fe films on Cu(lOO). It is proposed that a spin-density-wave (SDW) state is responsible for the magnetic structure. Based on the accurate thickness calibration, the borderlines of the three well-known regions with distinct magnetic properties are determined unambiguously for Fe films on Cu(100). A theoretically predicted temperature driven martensitic phase transition between regions II and III is indeed confirmed in experiment.
3. The single-crystalline Ni film with the body-centered-cubic(bcc) structure are obtained epitaxially on GaAs(001) surface at 170K. The in-plane and out-of-plane lattice constant of Ni/GaAs(100) was determined X-ray diffraction. And the magnetic properties and electron structure of bcc Ni have been studied with MOKE, FMR, SQUID, and Angle Resolved Photoemission.
4 Ultrathin Co films epitaxially grown on Pd(100) by Pulse Laser Deposition(PLD) and by normal Thermal Deposition(TD) was investigated respectively by in situ MOKE and Optical Ellipticmeter. The result demonstrates that the magnetic property strongly depends on interface condition. Magnetic-optical Kerr signal decreases abnormally in the PLD Co/Pd when Co is thicker than about
1ML. The total magnetic signal reach the minimum at about 1.3~1.4ML and then again increased linearly with the increasing of Co film thickness.
引文
1 G.A. Prinz, Physics Today, April (1995)
2 F. J. Himpsel, J. E. Ortega, G J. Mankey and R. F. Willis, Adv. Phys. 47, 511(1998)
3 J. Thomassen, B. Feldmann, M. Wutting, and H. Ibach, Phys. Rev. Lett. 69, 3831(1992)
4 G A. Prinz, Phys. Rev. Lett. 54, 1051(1981)
5 X.F. Jin, M. Zhang, G S. Dong, M. Xu, Y. Chen, X. Wang,X.G. Zhou, X.L. Shen, Appl. Phys. Lett. 65, 3078(1994)
6 N. Honda, K. Ouchi, J. Mag. Soc. Jap. 24, 1027(2000) .
7 T. Koide, H. Miyauchi, J. Okamoto, T. Shidara, A. Fujimori, H. Fukutani, K. Amemiya, H. Takeshita, S. Yuasa, T. Katayama, and Y. Suzuki, Phys. Rev. Lett. 87, 257201(2001) .
8 P. Grunberg, R. Schreiber, Y. Pang, M.B. Brodsky, H. Sowers, Phys. Rev. Lett. 57 (1986) 2442．
9 P. Bruno, C. Chappert, Phys. Rev. Lett. 67, 1602(1991) ; A. Bounouh, P. Beauvillain, P. Bruno, C. Chappert, R. Megy, P. Veillet, Euro. Lett. 33, 315(1996) .
10 Kawakami RK, Rotenberg E, Choi HJ, Escorcia-Aparicio E, Bowen MO, Wolfe JH, Arenholz E, Zhang ZD, Smith NV, Qiu ZQ, nature, 398, 6723(1999) .
11 S. N. Okuno, t. Kshi, and K. Tanaka, Phys. Rev. Lett. 88, 066803(2002) .
12 W.H. Meiklejohn, C.P. Bean, Phys. Rev. 102 (1956) 1413
13 A. E. Berkowitz, Kentaro Takano, J. Mag. Mag. Mater. 200,552(1999) ; H. Ohldag, T. J. Regan, J. Stohr,A. Scholl, F. Nolting, J. Luning, c. Stamm, S. Anders, and R. L. White, 87, 247201(2001) .
14 M.N. Baibich, J.M. Broto, A. Fert, F. Nguyen Van Dau, F. Petroff, P. Etienne, G. Creuzet, A. Friederich, J. Chazelas, Phys. Rev. Lett. 61 (1988) 2472．
15 G Binasch, P. Grunberg, F. Saurenbach, W. Zinn, Phys. Rev. B 39 (1989) 4828．
16 M. Julliuere, Phys. Lett. 54 A (1975) 225．
17 J.S. Moodera, L.R. Kinder, T.M. Wong, R. Meservey, Phys. Rev. Lett. 74 (1995) 3273．
18 Y. Tokura, Y. Tomioka, J. Mag. Mag. Mater. 200,1(1999) .
19 H. J. Zhu, M. Ramsteiner, H. Kostial, M. Wassermeier, H. P. Schonherr, and K. H. Ploog, Phys. Rev. Lett. 87,016601(2001) .
20 Y. Ohno, D. K. Young, B. Beschoten, F. Matsukura, H. Ohno, D. D. Awschalom, Nautre,402, 6763(1999) .
21 M. Pratzer, H. J. Elmers, M. Bode, O. Pietzsch, A. Kubetzka, R. Wiesendanger, Phys. Rev. Lett. 1, 17(2001) ; S. Heinze, M. Rode, A. Kubezka, O. Pietzsch, X. Nie, S. Bluel, R.l Wiesendanger, Science, 288, 54762,1805(2000) .
22 J. Stohr, A. Scholl, T. J. Regan, S. Anders, J. Luning, M. R. Scheinfein, H. A. Padmore, R. L. White, Phys. Rev. Lett. 83,1862(1999) ; A. Scholl, H. Ohldag, F. Nolting, J. Stohr, H. A. Padmore, Rev. Sci. Inst. 73,1362(2002) .
2 F. J. Himpsel, J. E. Ortega, G J. Mankey and R. F. Willis, Adv. Phys. 47, 511(1998)
3 J. Thomassen, B. Feldmann, M. Wutting, and H. Ibach, Phys. Rev. Lett. 69, 3831(1992)
4 G A. Prinz, Phys. Rev. Lett. 54, 1051(1981)
5 X.F. Jin, M. Zhang, G S. Dong, M. Xu, Y. Chen, X. Wang,X.G. Zhou, X.L. Shen, Appl. Phys. Lett. 65, 3078(1994)
6 N. Honda, K. Ouchi, J. Mag. Soc. Jap. 24, 1027(2000) .
7 T. Koide, H. Miyauchi, J. Okamoto, T. Shidara, A. Fujimori, H. Fukutani, K. Amemiya, H. Takeshita, S. Yuasa, T. Katayama, and Y. Suzuki, Phys. Rev. Lett. 87, 257201(2001) .
8 P. Grunberg, R. Schreiber, Y. Pang, M.B. Brodsky, H. Sowers, Phys. Rev. Lett. 57 (1986) 2442．
9 P. Bruno, C. Chappert, Phys. Rev. Lett. 67, 1602(1991) ; A. Bounouh, P. Beauvillain, P. Bruno, C. Chappert, R. Megy, P. Veillet, Euro. Lett. 33, 315(1996) .
10 Kawakami RK, Rotenberg E, Choi HJ, Escorcia-Aparicio E, Bowen MO, Wolfe JH, Arenholz E, Zhang ZD, Smith NV, Qiu ZQ, nature, 398, 6723(1999) .
11 S. N. Okuno, t. Kshi, and K. Tanaka, Phys. Rev. Lett. 88, 066803(2002) .
12 W.H. Meiklejohn, C.P. Bean, Phys. Rev. 102 (1956) 1413
13 A. E. Berkowitz, Kentaro Takano, J. Mag. Mag. Mater. 200,552(1999) ; H. Ohldag, T. J. Regan, J. Stohr,A. Scholl, F. Nolting, J. Luning, c. Stamm, S. Anders, and R. L. White, 87, 247201(2001) .
14 M.N. Baibich, J.M. Broto, A. Fert, F. Nguyen Van Dau, F. Petroff, P. Etienne, G. Creuzet, A. Friederich, J. Chazelas, Phys. Rev. Lett. 61 (1988) 2472．
15 G Binasch, P. Grunberg, F. Saurenbach, W. Zinn, Phys. Rev. B 39 (1989) 4828．
16 M. Julliuere, Phys. Lett. 54 A (1975) 225．
17 J.S. Moodera, L.R. Kinder, T.M. Wong, R. Meservey, Phys. Rev. Lett. 74 (1995) 3273．
18 Y. Tokura, Y. Tomioka, J. Mag. Mag. Mater. 200,1(1999) .
19 H. J. Zhu, M. Ramsteiner, H. Kostial, M. Wassermeier, H. P. Schonherr, and K. H. Ploog, Phys. Rev. Lett. 87,016601(2001) .
20 Y. Ohno, D. K. Young, B. Beschoten, F. Matsukura, H. Ohno, D. D. Awschalom, Nautre,402, 6763(1999) .
21 M. Pratzer, H. J. Elmers, M. Bode, O. Pietzsch, A. Kubetzka, R. Wiesendanger, Phys. Rev. Lett. 1, 17(2001) ; S. Heinze, M. Rode, A. Kubezka, O. Pietzsch, X. Nie, S. Bluel, R.l Wiesendanger, Science, 288, 54762,1805(2000) .
22 J. Stohr, A. Scholl, T. J. Regan, S. Anders, J. Luning, M. R. Scheinfein, H. A. Padmore, R. L. White, Phys. Rev. Lett. 83,1862(1999) ; A. Scholl, H. Ohldag, F. Nolting, J. Stohr, H. A. Padmore, Rev. Sci. Inst. 73,1362(2002) .