Microwave Absorption of Magnetic Antidot Arrays
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1248-D11-19
Microwave Absorption of Magnetic Antidot Arrays
Leszek M. Malkinski, Minghui Yu and Donald Scherer II Advanced Materials Research Institute, University of New Orleans, New Orleans, LA, USA
ABSTRACT Three antidot arrays with FeNi alloy thickness of 20, 50 and 100 nm have been patterned using magnetron sputtering followed by the electron-beam lithography and lift-off technique. Ferromagnetic resonance technique was used to study dynamic properties of the antidot arrays. These results were compared with the measurements of continuous films with the same composition and thickness. Two distinct resonant fields have been observed for the bias field aligned with the edges of the square holes. Resonance peaks shifted towards each other and eventually merged when the in-plane bias field was rotated towards diagonal of the squares. This dependence has been explained in terms of magnetostatic energy associated with the square holes. The magnitude of this effect was decreasing for the arrays with the reduced thickness. The perpendicular and lateral quantized standing spin wave modes were detected in the reference films and the antidot arrays due to the perpendicular and lateral dimensional confinements.
INTRODUCTION Increasing attention has been devoted to arrays of antidot because of the novel static and dynamic magnetic properties and their potential application for ultra-high density information storage [1-3]. The introduction of nonmagnetic holes into the continuous magnetic film significantly modifies the magnetic properties leading to unique domain configurations, interesting magnetoresistance behavior, and distinct ferromagnetic resonance spectra [4-7]. One of advantages of antidots over the magnetic dots is that unlike dots the perforated films are not subject to a superparamagnetic limit. Micromagnetic calculation by Zhu et al [8] indicates that the presence of holes in the network media improves the thermal stability and signal to noise ratio of conventional longitudinal media. The consecutive square holes could be used to record the memory bits [9]. The maximum areal density in the order of 750 Gbit/in2 was theoretically predicted by Torres et al in the antidot system with optimized material parameters and geometrical dimensions [3]. In our former work [10], we have successfully fabricated antidot arrays with different nanoscale sizes of square holes on top of Si substrate. In this contribution, we discuss static and dynamic magnetic properties of antidots with the fixed hole size and variable thickness of the FeNi alloy film.
EXPERIMENTAL Three square antidot arrays with different Py thickness (20, 50, and 100 nm) were fabricated using electron-beam lithography, magnetron sputtering and lift-off technique. A thin layer of polymethyl methacrylate (PMMA) 950A4 resist was spun onto Si (100) substrates at the spin rate of 3000 rpm. After PMMA was prebaked at 180 oC for 2 min on a hotplate, a pattern was written using electron beam of the LEO 1530 VP field emission
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