Ferromagnetic resonance with Scanning Tunneling Microscopy

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This project aims at the establishment of a new experimental method that combines high resolution spin-polarized scanning tunneling microscopy (Sp-STM) with the spin torque diode effect to realize spatially resolved ferromagnetic resonance and to study the magnetization dynamics of individual nano-sized magnetic structures including their magnetic eigen-modes. We mix a rf-voltage to the bias of the tunneling junction in order to periodically excite the magnetic sample by the resulting periodic spin torque. When hitting the resonance frequency, the combined periodic magnetization oscillations and the oscillating bias lead via the spin-dependent tunneling to a rectified dc-current that can be detected using conventional current amplifiers. This effect is known as the spin diode effect. In preliminary experiments we succeeded to compensate for transmission effects such that a constant excitation voltage can be reached as function of excitation frequency and have observed resonance signals in magnetic skyrmions. In this proposal, we intend to extend the frequency range (currently limited to 3GHz) to above 13 GHz and enlarge the excitation amplitude by an order of magnitude such that: 1. resonance phenomena of magnetic vortices can be studied in detail, 2. gyration and breathing modes of skyrmions can be detected and be compared with numerical simulations and 3. from the line shape of the resonance, contributions of the Slonczweski and field like spin torques can be determined.