The ability to study and control spin dynamics in a micro- to nano-sized magnet is important in the fast-evolving fields of spintronics and magnonics, areas of great interest for information storage and other potential applications. Ferromagnetic resonance (FMR) is a well-established technique for measuring dynamic magnetic properties of macro-sized samples like thin films, but recently a multinational team of researchers has demonstrated two different methods of increasing FMR spatial resolution for micro-resonators, improving detection sensitivity by four orders of magnitude. Their work is reported in Review of Scientific Instruments.

The first technique for investigating FMR excitations, scanning thermal microscopy (SThM)-FMR combines an atomic force microscope with a thermal tip with an FMR setup consisting of microwave synthesizer, magnet, micro-resonator, circulator and microwave diode. The second technique uses an experimental setup nearly identical to the one used for SThM-FMR, adding a microwave synthesizer and amplifier outside of the vacuum of a scanning X-ray transmission microscope (STXM) chamber to excite the specimen inside it. Proof-of-principle experiments using both methods were conducted by growing two perpendicular magnetic micro-stripes and then investigating their FMR excitations.

According to physicist Taddäus Schaffers, lead author, these methods are complementary to one another. SThM-FMR allows locally excited FMR to be detected down to 106 spins due to the use of micro-resonators, while by using micro-resonators researchers can conduct STXM-FMR experiments that combine unprecedented spatial and temporal resolution and the element specificity of the XMCD technique. Schaffers states that these two methods will help to deepen the understanding of dynamic magnetic behavior and provide better control of magnetism on the nanoscale.

Source: “The combination of micro-resonators with spatially resolved ferromagnetic resonance,” by T. Schaffers, R. Meckenstock, D. Spoddig, T. Feggeler, K. Ollefs, C. Schöppner, S. Bonetti, H. Ohldag, M. Farle, and A. Ney, Review of Scientific Instruments (2017). The article can be accessed at