Tuning the Lifetime and Spectral Readout of Single-Atom Magnets with a Vector Magnetic Field.

Magnetic atoms on insulating films are promising candidates for information storage at the atomic scale, but practical operation requires their magnetic lifetimes and readout to be controllable. Here, we study holmium (Ho) single-atom magnets on MgO using electron spin resonance scanning tunneling microscopy. The two magnetic states of Ho are written by current-induced switching with a spin-polarized tip and read remotely through the ESR resonance frequency of a nearby Ti atom, which senses the Ho dipolar field. By atomic manipulation, we construct a two Ho/one Ti structure in which the four Ho magnetic configurations are resolved as distinct Ti resonance frequencies and remain stable for up to 12 h. Rotating the external magnetic field changes the projection of the Ho dipolar fields onto the Ti-sensing axis, allowing the frequency separation between different magnetic configurations to be tuned. The same vector field control also modifies the Ho lifetime, while spatial mapping with the spin-polarized tip reveals a strong dependence of the switching dynamics on the local tip position. These results demonstrate vector field control of both the lifetime and frequency-resolved readout of surface-supported single-atom magnets.