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Stripe domains and magnetoresistance in thermally deposited nickel films
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) e1339–e1340
Stripe domains and magnetoresistance in thermally deposited nickel films P.D. Sparksa,*, N.P. Sterna, D.S. Snowdena, B.A. Kappusa, J.G. Checkelskya, S.S. Harbergera, A.M. Fusellob, J.C. Eckerta a
Department of Physics, 224 East Twelfth St., Harvey Mudd College, Claremont, CA 91711, USA b Department of Immunology, Washington University, St. Louis, MO, USA
Abstract We report a study of the domain structure and magnetoresistance of thermally deposited nickel films. For films thicker than 17 nm, we observe striped domains with period varying with film thickness as a power law with exponent 0.2170.02 up to 120 nm thickness. There is a negative magnetoresistance for fields out of the plane. r 2003 Elsevier B.V. All rights reserved. PACS: 75.60.Ch; 75.70.Kw Keywords: Striped domain; Nickel; Magnetoresistance
Striped magnetic domains have been observed in a wide variety of materials such as epitaxial Co [1] and epitaxial Ni [2] or amorphous Ni [3]. The period of the domains as a function of film thickness yields insight into the strain and magnetic anisotropy. In this work we report the first investigation of striped domains in thermally deposited Ni films and characterize the conditions for the formation of striped domains. We also measure the magnetoresistance of the films in the presence of the domains. Our results add further insight into the spin scattering in domain walls [4–6]. We use a standard thermal evaporator with a liquid nitrogen trapped diffusion pump. The evaporated source is 99.99% pure nickel in an alumina coated molybdenum boat. The substrates are glass cover slips. Standard base pressure is about 5 107 Torr with a liquid nitrogen trapped oil diffusion pump system. The maximum deposition pressure is 2 106 Torr. The deposition rates are 0.1–0.2 nm/s.
*Corresponding author. Tel.: +1-909-607-4038; fax: +1909-621-8887. E-mail address: [email protected] (P.D. Sparks).
The MFM images were made with a Digital Instruments Dimension 3000 using phase imaging and MESP tips. The sample geometry affects the magnetic domain structure. We studied films 1.5 cm 1.5 cm square and lines of width 100–300 mm and length 1 cm. The resistance is measured with the field parallel to or perpendicular to the current and in or out of the plane. The stripes are oriented by applying a field in the plane either parallel or perpendicular to the current. The orienting field begins at +8 T then sweeps to 4 T, +2 T, decreasing its range down to zero. Only the films patterned as lines show reproducible domain structure, so all magnetoresistance measurements are done on those. For ease in making contacts, the wider lines are used. The resistance measurements are made at 310 K using a Quantum Design Physical Properties Measurement System with a standard four-probe configuration. The current is 300 mA, with a maximum voltage and power of 10 mV and 100 mW, respectively to limit Joule heating. The current goes down the line. The domain structure was measured before and after resistance sweeps. The MFM images of the large square samples do not show striped domains except near the edges, particularly
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.586
ARTICLE IN PRESS e1340
P.D. Sparks et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1339–e1340
Fig. 1. MFM image of 80 nm Ni film after orienting stripes along field as shown. The period is 180710 nm.
Fig 3. Resistance vs. magnetic field for an 80 nm Ni film. The field is out of the plane and the initial domain walls are perpendicular to the current.
For fields out of the plane, a typical hysteresis curve is shown in Fig. 3 for a narrow line Ni film with t ¼ 80 nm and domain walls perpendicular to the current. The magnitude of the peak is approximately independent of film thickness at B0.3%. For fields in the plane, the magnetoresistance depends on the relative orientation of the current and the field. For example, for an 80 nm film, for currents parallel to the field, there are 1% minima at 7300 Oe and for fields perpendicular to the current, there are 1% maxima at 7300 Oe. Future measurements will characterize the magnetoresistance as a function of Ni film thickness.
Fig. 2. Log–log plot of domain stripe period vs. film thickness for Ni films. The slope is 0.217 0.02.
near corners where there is an effective patterning to smaller dimensions. The line samples show striped domains as shown in Fig. 1 over their entire area. Films thinner than 17 nm or with deposition rates below 0.15 nm/s do not show striped domains. The orientation of the stripes can be controlled by the applied magnetic field, and then it persists when the field is removed. The stripe period was analyzed using the FFT procedure. The resulting dominant length scale is plotted as a function of film thickness in Fig. 2. The results are in general agreement with Hameed [2], but there is a significant difference between epitaxial and thermally deposited films. The data are fit to a power law with P=Atx where P is the stripe period in nm when t is the film thickness in nm, A ¼ 7574; x ¼ 0:2170:02: The reduced w2 ¼ 0:6:
Acknowledgements This work was supported in part by the Harvey Mudd Research Committee, the Parsons Foundation, the Kresge Foundation and NSF Grant DUE-9850777.
References [1] J.F. Gregg, W. Allen, K. Ounadjela, M. Viret, S.M. Thompson, J.M.D. Coey, Phys. Rev. Lett. 77 (1996) 1580. [2] H.J. Hug, B. Stiefel, A. Moser, I. Parashikov, A. Klicznik, D. Lipp, H.-J. Guntherodt, G. Bochi, D.I. Paul, R.C. O’Handley, J. Appl. Phys. 79 (1996) 5609; S. Hameed, P. Talagala, M.R. Naik, L.E. Wenger, V.M. Naik, R. Proksch, Phys. Rev. B 64 (2001) 184406. [3] G. Skidmore, Ph.D. Thesis, University of Minnesota, 1998. [4] P.M. Levy, S. Zhang, Phys. Rev. Lett. 79 (1997) 5110. [5] M. Viret, et al., Phys. Rev. B. 53 (1996) 8464. [6] M. Viret, et al., Phys. Rev. Lett. 85 (2000) 3962.
Journal of Magnetism and Magnetic Materials 272–276 (2004) e1339–e1340
Stripe domains and magnetoresistance in thermally deposited nickel films P.D. Sparksa,*, N.P. Sterna, D.S. Snowdena, B.A. Kappusa, J.G. Checkelskya, S.S. Harbergera, A.M. Fusellob, J.C. Eckerta a
Department of Physics, 224 East Twelfth St., Harvey Mudd College, Claremont, CA 91711, USA b Department of Immunology, Washington University, St. Louis, MO, USA
Abstract We report a study of the domain structure and magnetoresistance of thermally deposited nickel films. For films thicker than 17 nm, we observe striped domains with period varying with film thickness as a power law with exponent 0.2170.02 up to 120 nm thickness. There is a negative magnetoresistance for fields out of the plane. r 2003 Elsevier B.V. All rights reserved. PACS: 75.60.Ch; 75.70.Kw Keywords: Striped domain; Nickel; Magnetoresistance
Striped magnetic domains have been observed in a wide variety of materials such as epitaxial Co [1] and epitaxial Ni [2] or amorphous Ni [3]. The period of the domains as a function of film thickness yields insight into the strain and magnetic anisotropy. In this work we report the first investigation of striped domains in thermally deposited Ni films and characterize the conditions for the formation of striped domains. We also measure the magnetoresistance of the films in the presence of the domains. Our results add further insight into the spin scattering in domain walls [4–6]. We use a standard thermal evaporator with a liquid nitrogen trapped diffusion pump. The evaporated source is 99.99% pure nickel in an alumina coated molybdenum boat. The substrates are glass cover slips. Standard base pressure is about 5 107 Torr with a liquid nitrogen trapped oil diffusion pump system. The maximum deposition pressure is 2 106 Torr. The deposition rates are 0.1–0.2 nm/s.
*Corresponding author. Tel.: +1-909-607-4038; fax: +1909-621-8887. E-mail address: [email protected] (P.D. Sparks).
The MFM images were made with a Digital Instruments Dimension 3000 using phase imaging and MESP tips. The sample geometry affects the magnetic domain structure. We studied films 1.5 cm 1.5 cm square and lines of width 100–300 mm and length 1 cm. The resistance is measured with the field parallel to or perpendicular to the current and in or out of the plane. The stripes are oriented by applying a field in the plane either parallel or perpendicular to the current. The orienting field begins at +8 T then sweeps to 4 T, +2 T, decreasing its range down to zero. Only the films patterned as lines show reproducible domain structure, so all magnetoresistance measurements are done on those. For ease in making contacts, the wider lines are used. The resistance measurements are made at 310 K using a Quantum Design Physical Properties Measurement System with a standard four-probe configuration. The current is 300 mA, with a maximum voltage and power of 10 mV and 100 mW, respectively to limit Joule heating. The current goes down the line. The domain structure was measured before and after resistance sweeps. The MFM images of the large square samples do not show striped domains except near the edges, particularly
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.586
ARTICLE IN PRESS e1340
P.D. Sparks et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1339–e1340
Fig. 1. MFM image of 80 nm Ni film after orienting stripes along field as shown. The period is 180710 nm.
Fig 3. Resistance vs. magnetic field for an 80 nm Ni film. The field is out of the plane and the initial domain walls are perpendicular to the current.
For fields out of the plane, a typical hysteresis curve is shown in Fig. 3 for a narrow line Ni film with t ¼ 80 nm and domain walls perpendicular to the current. The magnitude of the peak is approximately independent of film thickness at B0.3%. For fields in the plane, the magnetoresistance depends on the relative orientation of the current and the field. For example, for an 80 nm film, for currents parallel to the field, there are 1% minima at 7300 Oe and for fields perpendicular to the current, there are 1% maxima at 7300 Oe. Future measurements will characterize the magnetoresistance as a function of Ni film thickness.
Fig. 2. Log–log plot of domain stripe period vs. film thickness for Ni films. The slope is 0.217 0.02.
near corners where there is an effective patterning to smaller dimensions. The line samples show striped domains as shown in Fig. 1 over their entire area. Films thinner than 17 nm or with deposition rates below 0.15 nm/s do not show striped domains. The orientation of the stripes can be controlled by the applied magnetic field, and then it persists when the field is removed. The stripe period was analyzed using the FFT procedure. The resulting dominant length scale is plotted as a function of film thickness in Fig. 2. The results are in general agreement with Hameed [2], but there is a significant difference between epitaxial and thermally deposited films. The data are fit to a power law with P=Atx where P is the stripe period in nm when t is the film thickness in nm, A ¼ 7574; x ¼ 0:2170:02: The reduced w2 ¼ 0:6:
Acknowledgements This work was supported in part by the Harvey Mudd Research Committee, the Parsons Foundation, the Kresge Foundation and NSF Grant DUE-9850777.
References [1] J.F. Gregg, W. Allen, K. Ounadjela, M. Viret, S.M. Thompson, J.M.D. Coey, Phys. Rev. Lett. 77 (1996) 1580. [2] H.J. Hug, B. Stiefel, A. Moser, I. Parashikov, A. Klicznik, D. Lipp, H.-J. Guntherodt, G. Bochi, D.I. Paul, R.C. O’Handley, J. Appl. Phys. 79 (1996) 5609; S. Hameed, P. Talagala, M.R. Naik, L.E. Wenger, V.M. Naik, R. Proksch, Phys. Rev. B 64 (2001) 184406. [3] G. Skidmore, Ph.D. Thesis, University of Minnesota, 1998. [4] P.M. Levy, S. Zhang, Phys. Rev. Lett. 79 (1997) 5110. [5] M. Viret, et al., Phys. Rev. B. 53 (1996) 8464. [6] M. Viret, et al., Phys. Rev. Lett. 85 (2000) 3962.