Localized Ferromagnetic Resonance Force Microscopy of a Continuous Permalloy-Cobalt Film
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1025-B11-18
Localized Ferromagnetic Resonance Force Microscopy of a Continuous Permalloy-Cobalt Film Evgueni Nazaretski1, Denis V. Pelekhov2, Ivar Martin1, Kitty C. Cha1, Elshan A. Akhadov1, P. Chris Hammel2, and Roman Movshovich1 1 Los Alamos National Laboratory, Los Alamos, NM, 87545 2 Ohio State University, Columbus, OH, 43210 ABSTRACT We report on the Magnetic Resonance Force Microscopy (MRFM) experiments performed on a 50 nm thick permalloy and a combined 20 nm thick permalloy – cobalt film. We studied the evolution of the MRFM spectra as a function of the vertical probe-sample distance and the lateral position as probe was scanned across the permalloy/cobalt interface. Our numerical simulations of the ferromagnetic resonance (FMR) modes excited in the presence of a non-uniform tip field of the cantilever compare well with experimental findings. This work demonstrates the capability of MRFM to perform local FMR spectroscopy of different materials in continuous ferromagnetic films. INTRODUCTION Magnetic resonance force microscopy, a novel type of scanning probe technique, attracted a lot of interest in the past decade due to its high force sensitivity and potential for excellent spatial resolution [1-2]. Recently, ferromagnetic resonance has been detected by MRFM technique [3]. Contrary to electron spin and nuclear magnetic resonance experiments, where the spatial image reconstruction has been successfully demonstrated [4-5], spatially resolved FMR poses a challenge due to the presence of a strong exchange coupling between spins. Ferromagnetic resonance spectra usually involve precession of the magnetization in the entire sample, and locally resolved FMR is not possible with conventional techniques. Recently developed scanning thermal microscopy is capable of local coupling to ferromagnetic resonance modes, however, it does not allow for spatially confined FMR excitation in continuous ferromagnetic samples [6]. We performed MRFM experiments with the probe in close proximity to the sample. In this regime the MRFM tip field is significant, and strongly modifies the ferromagnetic resonance modes, as well as leads to the formation of the local resonance under the tip. Here, we report MRFM spectra from a continuous, 50 nm thick permalloy and 20 nm thick combined permalloy-cobalt films, performed with a cantilever with a nearly spherical micron-size magnetic tip. We report the evolution of the MRFM spectra as a function of the tipsample spacing, and propose a model which describes the observed behavior. We also scanned the cantilever across the permalloy-cobalt interface, thus demonstrating the capability of MRFM to perform local FMR spectroscopy of different ferromagnetic materials. EXPERIMENTAL DETAILS Mechanical detection of magnetic resonance is based on the magnetic force originating from the interaction between spins in a sample and a permanent magnet mounted on a high quality-factor micromechanical cantilever [7]. We use a commercially available silicon nitride
cantilever with a fundamental resonant frequenc
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