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Magnet stability in individual rare earth atoms
Speaker Speaker: Dr. Fabio Donati
Affiliato Affiliato: Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland
Data Evento Lunedì 10 Luglio 2017, alle ore 16.00 - Aula Seminari Dipartimento di Fisica, Cubo 31C piano ponte pedonale
The need of downscaling and increasing the storage capability of magnetic memory devices is constantly pushing the research towards the ultimate reduction of the bit size. The outstanding evolution of technology seen in the last decades is now approaching the physical limit where quantum effects start to become relevant. On a more fundamental level, the research has increasingly focused on realizing information storage in the smallest unit of matter, i.e., a single magnetic atom adsorbed on a supporting substrate. To achieve this goal, it is required to stabilize the magnetic moment of the atom against thermal and quantum fluctuations. This imposes a careful engineering of the atom-surface interaction in order to maximize the magnetic anisotropy energy [1,2] and to protect the magnetic quantum levels against quantum tunneling of the magnetization and scattering with the electrons of the substrate [3].
Nevertheless, the goal of magnetic stability in single atoms has remained elusive for more than a decade.
In this talk, I will show the recent progresses in this research field. I will show that magnetic stability over a timescale of thousands seconds can be achieved using single rare earth atoms adsorbed on ultra-thin decoupling layers grown on a metal substrate. First, using X-ray magnetic circular dichroism (XMCD) we found that Ho atoms adsorbed on MgO/Ag(100) exhibit a spin lifetime of 1500 s at 10 K and open hysteresis loops up to 40 K [4]. These features qualify them as the first single atom magnets. Second, combining XMCD with scanning tunneling microscopy, we realized a model bit patterned media made of single Dy atoms. When deposited on graphene/Ir(111), these atoms exhibit magnetic stability at 2.5 K [5]. In addition, the moire pattern originating from the graphene/Ir lattice mismatch drives a self-assembly mechanism, which allows organizing the Dy atoms into ordered arrays. Our results unravel a novel class of magnetic materials that can be tailored at the atomic scale, paving the road to single-atom magnetic information storage.