Ferromagnetic Resonance Force Microscopy

Abstract

The magnetic resonance force microscope (MRFM) is a novel scanning probe instrument that combines the three-dimensional imaging capabilities of magnetic resonance imaging (MRI) with the high sensitivity and resolution of atomic force microscopy (AFM). In the nuclear magnetic resonance (NMR) mode or the electron spin resonance (ESR) mode it will enable nondestructive, chemical-specific, high-resolution microscopic studies and imaging of subsurface properties of a broad range of materials. In its most successful application to date, MRFM has been used to study microscopic ferromagnets. In ferromagnets the long-range spin–spin couplings preclude localized excitation of individual spins. Rather, the excitations employed in ferromagnetic resonance (FMR) are the normal magnetostatic wave (or spin-wave) modes determined by the geometry of the sample. In this case the response of the cantilever will be a measure of the amplitude of the FMR signal integrated over the volume where the magnetic field gradient of the tip magnet is significant. Thus, as the magnetic tip is scanned across the material under study, the signal intensity will be proportional to the local amplitude of the normal modes. In addition, the MRFM technique has proven useful for the observation of relaxation processes in microscopic samples. The MRFM will also enable the microscopic investigations of the nonequilibrium spin polarization resulting from spin injection. Microscopic MRFM studies will provide unprecedented insight into the physics of magnetic and spin-based materials at micrometer and submicrometer dimensions.