Fig. 3: MOKE hysteresis loops with MFM imaging for selected voltage-actuation times and XMCD-PEEM imaging.

a Hysteresis loop and MFM phase images of one of the disks measured after short-time voltage actuation (–25 V), corresponding to the formation of thin ferromagnetic layer. The shape of the hysteresis loop, together with the observed rotation of dipolar contrasts, shows that in such thin magnetic layers, magnetization reversal proceeds via coherent rotation. b Hysteresis loop and MFM phase images measured after long-time voltage actuation, corresponding to the formation of a thick ferromagnetic layer. In this case, the obtained results reveal that magnetization reversal occurs through formation of a swirling spin (i.e., vortion) state. c MFM phase image of three adjacent nanodots, measured near coercivity after long-term negative voltage treatment (i.e. 150 min at –25 V), where vortex cores can be envisaged, as indicated by dashed lines for one nanodot. XMCD-PEEM images recorded at the Co L₃ absorption edge and near coercivity for an array of six 280 nm FeCo(N) nanodots (d), single 280 nm FeCo(N) dot (e) and a single 1 µm FeCo(N) dot (f) after long-term voltage treatment at –25 V. Characteristic bright-dark magnetic contrast, observed for both dot diameters, demonstrates the presence of the magnetic vortex state, where the blue arrows represent the average spin direction in certain areas of the dot.