Magnetization, Magnetotransport and Ferromagnetic Resonance in A Permalloy Antidot Array with Square Holes
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0998-J05-19
Magnetization, Magnetotransport and Ferromagnetic Resonance in A Permalloy Antidot Array with Square Holes Minghui Yu, Leszek Malkinski, Leonard Spinu, and Weilie Zhou Advanced Materials Research Institute, University of New Orleans, 2000 Lakeshore Dr, New Orleans, LA, 70148
ABSTRACT A Permalloy antidot array with square hole size 800×800 nm2 has been fabricated by the means of electron-beam lithography and lift-off techniques. An out-of-plane anisotropy was found in both the reference film of Permalloy and the antidot array with the thickness of 100 nm. Inhomogeneous current-density distribution and complex domain structures in the antidot nanostructure result in unique behavior of the magnetoresistance. Quantized standing spin-wave modes originating from the lateral confinement of the antidot nanostructure were clearly observed for the magnetic field applied normal to the array plane. Two uniform precession resonance modes occurred when the field deviated more than 30 degrees from the normal to the plane. These two resonances originate from different regions of the array having distinct dipolar field patterns with different orientation and magnitude of magnetostatic field. The easy axes of the anisotropy in these regions are in-plane and orthogonal to each other. INTRODUCTION Arrays of antidot have attracted a lot of attention because of their potential application for ultra-high density data storage [1,2]. Micromagnetic numerical calculation by Cowburn et al. [3] showed that demagnetizing field produced by magnetic charges on edges of the antidot leads to a spatially variant shape anisotropy field. Competition between the shape anisotropy field and intrinsic uniaxial anisotropy produces regions which are magnetically softer. The remanent states in these regions can be used to store individual memory bit. Attractive advantage of antidots over dots is that they can overcome superparamagnetic limitation and retain Curie temperature because the memory bits in the antidot are not physically separated but coupled by magnetically hard regions. This makes antidots a very promising candidate for future ultra-high density data storage. Recently, many publications have reported the magnetic reversal and magnetotransport properties in the antidot arrays, e.g. [1,2,4]. In contrast, relatively few investigations have been devoted to study dynamic magnetic properties in antidot arrays, especially those with characteristic size smaller than micrometer. Recently, we have successfully fabricated lithographically patterned antidot arrays with square hole size of 800×800 nm2 on top of Si substrate. The detailed study on magnetization, magnetotransport and dynamic magnetic properties of the lithographically patterned nanoscale antidot array is presented in this contribution.
EXPERIMENTAL DETAILS The square antidot array with permalloy thickness of 100 nm were fabricated using electronbeam lithography and lift-off techniques. First, a thin layer of polymethyl methacrylate (PMMA) resist was spun onto Si (100) substrates
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