Fabian Donat Natterer, EPFL, Lausanne

Jeudi 29 Juin 2017 à 14h00
Amphi Holweck, Esc C
1ème etage

Stability of a holmium single atom magnet at high temperature and in a magnetic field

A common bar magnet has a permanent magnetization that is fixed in time. If we split this magnet, both halves will also have stable North and South poles. As the size of the fragmented magnets becomes smaller, the magnetization starts to spontaneously fluctuate owing to the onset of quantum tunneling of their magnetization [1]. The critical size at which the magnets seize to be stable ranges from only a few atoms to hundreds. However, a recent report of magnetic remanence for ensembles of single holmium atoms on magnesium oxide [2] cleared the way for a new era of ultra-dense magnetic data storage. At the fundamental limit of a single atom, however, the question of how to read and write the magnetic states remained. Here we show the control of the magnetization of selected Ho atoms by scanning tunneling microscopy (STM) [3] using current pulses, tunnel magnetoresistance (TMR), and STM enabled electron-spin resonance (ESR) [4]. Below a tunneling voltage threshold, the individual Ho bits remain stable for hours. We use this stability to build a prototypical two Ho bit atomic memory device to which we write the four possible states and which we read out via TMR and ESR. We further investigate the reversal mechanism above the switching threshold voltage at high magnetic field and at temperatures exceeding 40 K [5].

[1] Gatteschi and Sessoli, Angew. Chem. Int. Ed. 42, 268 (2003)
[2] Donati et al., Science 352, 318 (2016)
[3] Natterer et al., Nature 543, 226 (2017)
[4] Baumann, Paul et al., Science 350, 417 (2015)
[5] Natterer et al., in preparation

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