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Physica B: Condensed Matter
Volume 283, Issues 1-3, June 2000, Pages 162-166

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PII: S0921-4526(99)01920-1
Copyright © 2000 Elsevier Science B.V. All rights reserved.

Polarized neutron reflectivity characterization of weakly coupled Co/Cu multilayers

J. A. Borchers ^,^,^a, J. A. Dura^a, C. F. Majkrzak^a, S. Y. Hsu^b, R. Lolee^b, W. P. Pratt^b and J. Bass^b

^a NIST Center for Neutron Research, National Institute of Standards and Technology, 100 Bureau Drive STOP 8562, Gaithersburg, MD 20899-8562, USA
^b Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA

Available online 10 April 2000.

Abstract

Room temperature resistivity studies on (1 1 1) Co(6 nm)/Cu(6 nm) multilayers with weak interlayer coupling yield a giant magnetoresistance (GMR) of several percent for the as-prepared state relative to the saturated (i.e., large magnetic field) state. After application of a magnetic field, the magnetoresistance for the coercive state is only half to two-thirds as large. Using specular and off-specular polarized neutron reflectivity, we have determined the magnetic structure of these multilayers in the as-prepared and coercive states. Measurements of as-prepared samples show a strong antiparallel correlation of in-plane ferromagnetic Co domains across the Cu interlayers. At the coercive field, the Co domains are uncorrelated along the growth direction. Thus, the larger GMR for the as-prepared state arises from long-range antiparallel magnetic order along the growth-axis direction that is destroyed upon application of a magnetic field. For both the as-prepared and coercive states, the size of the in-plane ferromagnetic domains is approximately 0.5_¯1.5 small mu, Greek m. These domains give rise to pronounced diffuse scattering in rocking curves through the antiferromagnetic peak position.

Author Keywords: Giant magnetoresistance; Magnetic multilayer; Off-specular scattering; Magnetic domains; Polarized neutron reflectivity

Article Outline

Acknowledgements
References

(5K)
Fig. 1. Specular PNR as a function of Q_z=(4 small pi, Greek

) sin

for [Co(6 nm)|Cu(6 nm)]₂₀ in the as-prepared state in a 1.5 Oe field. The diffuse scattering has been subtracted, and the data have been corrected for the polarization efficiencies. The open and shaded circles correspond to the (--) and (++) data respectively. The open and shaded squares designate the (+-) and (-+) data. The arrows point to the appropriate vertical axis for the NSF and SF data.

(7K)
Fig. 2. Total PNR (shaded symbols) relative to the diffuse scattering (open symbols) for [Co(6 nm)|Cu(6 nm)]₂₀ and [Co(6 nm)|Cu(6 nm)]₂₀ (#2) in the as-prepared state. The diffuse scattering was measured by offsetting the angle by a small amount and then scanning Q_z. The circles and squares correspond to (--) and (++) data, respectively. The up and down triangles mark (+-) and (-+). No data corrections have been made. The arrows designate the vertical axis for each cross section. The inset shows the magnetic structure.

(14K)
Fig. 3. Transverse Q_x scans at the half-order position (Q_z=0.314 Å^-1) for [Co(6 nm)|Cu(6 nm)]₂₀ in the as-prepared (shaded symbols) and saturated (H=400 Oe) states (open symbols). The (++) and (--) NSF cross sections (circles and diamonds respectively) are shown in (a) and the (-+) and (+-) SF cross sections (squares and triangles) are shown in (b).

(7K)
Fig. 4. Transverse Q_x scans at the first-order position (Q_z=0.575 Å^-1) for [Co(6 nm)|Cu(6 nm)]₂₀ in the as-prepared state (shaded symbols) relative to the saturated state (open symbols) in H=400 Oe. Only the NSF cross sections are shown. The 400 Oe (--) data (circles) and (++) data (squares) are split because the Co moments are aligned parallel to the field. Insets (a) and (b) show multilayers with in-plane domains and magnetic roughness, respectively.

References

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Corresponding author. Tel.: +1-301-97-56-597; email: julie.borchers@nist.gov

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Physica B: Condensed Matter
Volume 283, Issues 1-3, June 2000, Pages 162-166

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