AVS 62nd International Symposium & Exhibition
    Scanning Probe Microscopy Focus Topic Thursday Sessions
       Session SP-ThP

Paper SP-ThP1
Extreme Magnetic Properties of Co Atoms on MgO Films

Thursday, October 22, 2015, 6:00 pm, Room Hall 3

Session: Scanning Probe Microscopy Poster Session
Presenter: Christopher Lutz, IBM Research - Almaden
Authors: C.P. Lutz, IBM Research - Almaden
S. Baumann, IBM Research - Almaden
A. Heinrich, IBM Research - Almaden
W. Paul, IBM Research - Almaden
T. Choi, IBM Research - Almaden
Correspondent: Click to Email
The magnetic moment of a free atom arises from the spin and orbital angular momentum. In a solid state environment, anisotropy in the orbital moment due to the ligand field, together with spin-orbit coupling, gives directionality and stability to the magnetization. Here we use a low-temperature scanning tunneling microscope (STM) to show that Co atoms bound to O sites on a MgO layer achieve a record-high zero-field splitting of 58 meV, which closely approaches the theoretical limit given by the spin-orbit coupling in a 3d transition metal atom. The zero-field splitting gives the energy of the first quantum step required to surmount the anisotropy barrier and reverse the magnetization. The combination of large moment and large anisotropy energy results in magnetic-state lifetimes exceeding 0.2 ms. The high symmetry of the Co atom's binding site gives a ligand field that is effectively cylindrical, which yields a large axial anisotropy while preserving nearly all of the free-atom's orbital angular momentum. All-electrical pump-probe measurements reveal the large magentic moment (5.5 μB) directly in STM. These results provide a symmetry-based strategy for the design of stable nanomagnets.