As the integrated circuits continue to shrink, the spin-based devices are intensively receiving the research focuses due to their advantages, such as the fast operation and low-power consumption compared to the electronic devices. To operate the spintronic devices at the nanoscale, the localized control of magnetic moments of individual atoms or atomic clusters is required. At these scales, a versatile way to control the spin quantization axis is to apply the exchange bias at the single-atom level. In this paper, published in Phys Rev Lett., we present a technique to control the exchange bias applied to a single atom on a surface over four orders of magnitude. The exchange interaction is continuously tunable from milli-eV to micro-eV by adjusting the separation between the spin-1/2 atom on the surface and the magnetic tip of a scanning tunneling microscope (STM). Here, combining the two spectroscopic techniques, inelastic electron tunneling spectroscopy (IETS) and electron spin resonance (ESR), enables us to map out the exchange interaction over a wide span of energies. In addition, we show that a time-varying exchange interaction provides a localized AC magnetic field that resonantly drives the surface spin. The static and dynamic control of the exchange interaction at the atomic-scale provides a route towards tailored spin-based devices and materials.
Shrinking spintronic devices to the nanoscale ultimately requires localized control of individual atomic magnetic moments. At these length scales, the exchange interaction plays important roles, such as in the stabilization of spin-quantization axes, the production of spin frustration, and creation of magnetic ordering. Here, we demonstrate the precise control of the exchange bias experienced by a single atom on a surface, covering an energy range of 4 orders of magnitude. The exchange interaction is continuously tunable from milli-eV to micro-eV by adjusting the separation between a spin-1/2 atom on a surface and the magnetic tip of a scanning tunneling microscope. We seamlessly combine inelastic electron tunneling spectroscopy and electron spin resonance to map out the different energy scales. This control of exchange bias over a wide span of energies provides versatile control of spin states, with applications ranging from precise tuning of quantum state properties, to strong exchange bias for local spin doping. In addition, we show that a time-varying exchange interaction generates a localized ac magnetic field that resonantly drives the surface spin. The static and dynamic control of the exchange interaction at the atomic scale provides a new tool to tune the quantum states of coupled-spin systems.