Magnetostatic Interactions of Two-Dimensional Arrays of Magnetic Strips
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1250-G08-03
Magnetostatic Interactions of Two-Dimensional Arrays of Magnetic Strips.
Leszek M. Malkinski, Minghui Yu and Donald J. Scherer II
Advanced Materials Research Institute, University of New Orleans, New Orleans, LA 70148, U.S.A
ABSTRACT A series of arrays consisting of Permalloy stripes with dimensions of 100 nm x 300 nm x 1500 nm were fabricated using electron beam nanolithography and magnetron sputtering followed by the lift-off process. In order to elucidate the effect of magnetostatic interactions among nanosized stripes on magnetic properties of the arrays, the separation between the stripes in different arrays was varied in the range between 100 nm and 2000 nm. Magnetic hysteresis loops of the arrays were measured using SQUID magnetometer for different orientations of the applied field with respect to the arrays. Magnetic anisotropy of the arrays was determined based on ferromagnetic resonance measurements at 9.8 GHz using EPR spectrometer. The measurements were carried out for different directions of the in-plane magnetic bias filed. The angular dependence of the resonance field of the main resonant peak indicated presence of the uniaxial magnetic anisotropy due to elongated shape of the stripes. Comparison between angular curves of resonant fields for different arrays leads to the conclusion that increasing strength of magnetostatic interactions among the stripes leads to a suppression of the uniaxial anisotropy. The stripes separated by 2000 nm behave almost like non-interacting objects, but the effect of interactions becomes particularly significant for separations smaller than 600 nm. The properties of the arrays with the smallest separations resembled those of continuous films. Magnetostatic modes have been observed in the FMR spectra in addition to the main resonant peak. These modes are believed to result from dimensional confinement of lateral spinwaves in the magnetic stripes. No such modes were observed in the reference samples of solid Py films, with the in-plane applied magnetic field. INTRODUCTION Dynamically developing applications, in the fields of wireless communication and information technology, require advanced magnetic materials operating at microwave frequencies [1-4]. Technology of conventional magnetic microwave materials with complex structures, such as: spinels, hexaferrites or garnets, cannot be easily integrated with current silicone technology of electronic circuits. Therefore, there is an increasing demand for developing new materials for microwave applications. Metallic nanostructures of transition metals with large magnetization seem to be good candidates for high frequency devices. The problem of losses, due to eddy
currents, which limit frequency of applications of bulk metals, is greatly reduced because of reduced dimensionality of nanostructures. Our preliminary results on arrays of magnetic stripes or antidots indicate that magnetostatic fields have pronounced effect on their magnetic behavior at microwave region [5-7]. One of the effects of magnetostatic fie
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