Who: Dr. Fabio Donati, IBS Center for Quantum Nanoscience, Seoul, Korea
Place: Donostia International Physics Center
Date: Friday, 25 May 2018, 12:00
Atomic-scale magnets with long magnetic lifetimes represent the smallest unit of matter that can be used to store and manipulate information. Understanding their properties is the key to reach the ultimate downscaling of magnetic memories. The main requirement of a magnetic bit is to retain a net magnetization in absence of magnetic field on a long timescale. The fingerprint of this feature is the remanence in magnetic hysteresis loops.
Electron spins in single atoms on surfaces can be addressed both with ensemble X-ray magnetic circular dichroism (XMCD) and with scanning tunneling microscopy (STM). The latter allows the control and manipulation of individual spins with atomic precision. These techniques have been used to pioneer the magnetism of rare earth atoms on surfaces [1,2]. Due to the strong localization of the 4f electrons, the spins of these atoms weakly interact with the environment and can have magnetic lifetimes of the order of thousands of seconds at 2.5 K [3,4]. The possibility of reading and writing their magnetic states at the atomic scale demonstrated the potential of these atoms as magnetic bits .
In this presentation, I will describe the recent advances in the field that leaded to the discovery of magnetic remanence in Ho atoms on MgO/Ag(100). Using XMCD, we demonstrated that these atoms exhibit magnetic lifetimes on the timescale of thousands of seconds at 2.5 K. These features qualify them as the first single atom magnets. Remarkably, they exhibit an exceptional magnetic stability up to 30 K . Using STM in high magnetic fields, we identify the threshold of their spontaneous magnetic relaxation at about 45 K, where spin fluctuations occurs on the time scale of tens of seconds. Finally, I will discuss the present understanding about the magnetic behavior of Ho atoms and the hints for designing novel single atom magnets with magnetic stability at even higher temperatures.
 T. Myamachi et al., Nature 503, 242 (2013)
 F. Donati et al., Phys. Rev. Lett. 113, 237201 (2014)
 F. Donati et al., Science 352, 318 (2016)
 R. Baltic et al., Nano Lett. 16, 7610 (2016)
 F. D. Natterer et al., Nature 543, 226 (2017).
 F. D. Natterer et al, arXiv:1712.07871.