The magnetic-resonance force microscope: a new tool for high-resolution, 3-D, subsurface scanned probe imaging

The magnetic-resonance force microscope (MRFM) is a novel scanned probe instrument which combines the three-dimensional (3-D) imaging capabilities of magnetic-resonance imaging with the high sensitivity and resolution of atomic-force microscopy. It will enable nondestructive, chemical-specific, high-resolution microscopic studies and imaging of subsurface properties of a broad range of materials. The MRFM has demonstrated its utility for study of microscopic ferromagnets, and it will enable microscopic understanding 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. We will describe the principles and the state-of-the-art in magnetic-resonance force microscopy, discuss existing cryogenic MRFM instruments incorporating high-Q, single-crystal microresonators with integral submicrometer probe magnets, and indicate future directions for enhancing MRFM instrument capabilities

Ferromagnetic dynamics detected via one- and two-magnon NV relaxometry

The NV center in diamond has proven to be a powerful tool for locally characterizing the magnetic response of microwave excited ferromagnets. To date, this has been limited by the requirement that the FMR excitation frequency be less than the NV spin resonance frequency. Here we report NV relaxometry based on a two-magnon Raman-like process, enabling detection of FMR at frequencies higher than the NV frequency. For high microwave drive powers, we observe an unexpected field-shift of the NV response relative to a simultaneous microwave absorption signal from a low damping ferrite film. We show that the field-shifted NV response is due to a second order Suhl instability. The instability creates a large population of non-equilibrium magnons which relax the NV spin, even when the uniform mode FMR frequency exceeds that of the NV spin resonance frequency, hence ruling out the possibility that the NV is relaxed by a single NV-resonant magnon. We argue that at high frequencies the NV response is due to a two-magnon relaxation process in which the difference frequency of two magnons matches the NV frequency, and at low frequencies we evaluate the lineshape of the one-magnon NV relaxometry response using spinwave instability theory

Light-free magnetic resonance force microscopy for studies of electron spin polarized systems

Magnetic resonance force microscopy is a scanned probe technique capable of three-dimensional magnetic resonance imaging. Its excellent sensitivity opens the possibility for magnetic resonance studies of spin accumulation resulting from the injection of spin polarized currents into a para-magnetic collector. The method is based on mechanical detection of magnetic resonance which requires low noise detection of cantilever displacement; so far, this has been accomplished using optical interferometry. This is undesirable for experiments on doped silicon, where the presence of light is known to enhance spin relaxation rates. We report a non-optical displacement detection scheme based on sensitive microwave capacitive readout