Theory of a Spintronic Nano-Scale Microwave Diode for Applications in Microwave Energy Harvesting
Technical rept. 1 Oct 2010-28 Feb 2012
OAKLAND UNIV ROCHESTER MI DEPT OF PHYSICS
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We report on a spectroscopic study of the spin-wave eigen-modes inside an individual normally magnetized two layers circular nano-pillar PermalloyCopperPermalloy by means of a Magnetic Resonance Force Microscope MRFM. We demonstrate that the observed spin-wave spectrum critically depends on the method of excitation. While the spatially uniform radio-frequency RF magnetic field excites only the axially symmetric modes having azimuthal index l 0, the RF current flowing through the nano-pillar, creating a circular RF Oersted field, excites only the modes having azimuthal index l 1. Breaking the axial symmetry of the nano-pillar, either by tilting the bias magnetic field or by making the pillar shape elliptical, mixes different l-index symmetries, which can be excited simultaneously by the RF current. Experimental spectra are compared to theoretical prediction using both analytical and numerical calculations. An analysis of the influence of the static and dynamic dipolar coupling between the nano-pillar magnetic layers on the mode spectrum is performed.
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