Abstract

Polarized neutron reflectometry (PNR) has recently been applied to study lateral magnetic structures such as regular micron-sized magnetic arrays on a surface. To date, however, there is a lack of detailed accounts of the features observed in the scattered intensity map in the special case of time-of-flight (TOF) PNR. We present here preliminary measurement results on lithographically produced arrays of micron-sized rectangular permalloy magnetic bars. The measurements demonstrate the potential of the method to provide detailed structural information on a laterally patterned sample, as well as on its magnetic characteristics. The information can be obtained by analyzing the specular reflection along with three off-specular Bragg sheets. Most of the features seen experimentally can be interpreted by using simple heuristic arguments. In addition, we also present results of a study of lateral magnetic domains in an exchange-biased Co/CoO bilayer film to illustrate the capability of TOF PNR in the study of large lateral magnetic domains in the case when almost no off-specular scattering is detected.

Author Keywords: Time-of-flight neutron reflectometry; Off-specular scattering; Specular reflection; Distorted-wave Born approximation; Patterned magnetic arrays; Lateral magnetic domains

PACS classification codes: 61.12.Ha; 61.10.Bt; 75.70.Kw; 75.70.Cn

Article Outline

• Acknowledgements

• References

(12K)
Fig. 1. AFM image of the micron-sized magnetic elements on a silicon surface.

(20K)
Fig. 2. Log-scale intensity map for (a) spin-up and (b) spin-down incident neutrons scattered from an array of micron-sized magnetic elements on a silicon surface. The solid line at 1.08° is the horizon. The dotted lines are calculated locations of: (1) specular reflection; (2, 3) off-specular reflections; and (4) diffraction. The dashed lines are the critical edges (from the horizon to higher/lower angles): the silicon edge (above the horizon only) and the permalloy edges corresponding to SLD Nb_c+ and Nb_c−.

(25K)
Fig. 3. Reflectivities of an exchange-biased CoO/Co bilayer at 10 K: (a) R⁺ (filled symbols) and R⁻ (open symbols) at H=+200 Oe (circle), +450 Oe (square), and +5 kOe (lower triangle); (b) R⁻⁺ at H=+200 Oe (filled circle), +450 Oe (square), +5 kOe (lower triangle), and R⁻⁺(90°) (upper triangle). The inset in (a) shows the hysteresis (solid line) at 10 K and the normalized magnetization obtained from R⁺ and R⁻. (c) Magnetic domain dispersion ² of the CoO/Co bilayer at 10 K and H=+200 Oe (filled circle), and +450 Oe (square). Data taken at reversal at +350 Oe is included for comparison (upper triangle).

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Corresponding author. Tel.: +1-630-252-5285; fax: +1-630-252-4163

¹ Current address: Argone National Laboratory, IL 60439, USA.