Fig. 5
Two-bit register and four-state memory based on giant moment clusters. a–d Spin-resolved constant-current images of two fcc top clusters in the four possible spin states (01), (11), (10), and (00), where 0 and 1 correspond to downwards and upwards pointing magnetization, respectively (imaging parameters: V = −1 mV, I = 500 pA, B = 0 T, T = 0.3 K). The Fe atom in the back serves as a marker for the apparent height. The scale bar defines a length of 1 nm. Between the images, the tip was positioned on top of the cluster whose state was intended to be changed, the bias was slowly increased until the state switched, and then quickly decreased to the imaging parameter. e The long-term stability of one of the two magnetic bits is shown by measuring the height of the cluster (orange trace) in the state 0 over more than 10 h (V = −0.7 mV, I = −50 pA, B = 0 T, T = 0.3 K), without a single switch into the state 1, whose height reference is given by the red dotted line, which was determined from the magnetic contrast in images a–d. f–i, Top view schematic diagram of a possible memory with four different realized spin states on a hcp hollow cluster. The two upper circles in each panel illustrate two fcc top clusters prepared in magnetization states up (dot) or down (cross). The lower circle in each panel signifies a hcp hollow cluster (or a hcp atom), which is forced into one of the four spin states indicated by the thick arrow, as dictated by the Dzyaloshinskii–Moriya interaction D (orientation indicated by the two thin arrows) to the two neighboring clusters
