Figure 3: Saturated magnetic state and magnetization reversal process in N=8 unit cells sample.
From: Emergent nanoscale superparamagnetism at oxide interfaces
(a–d) Bz(x,y) images of 1.3 × 1.4 μm2 after ZFC (a), after excursion to 
 mT (b), after excursion to 
 mT (c), and in the presence of 
 mT (enhancing instrumental noise) (d). The dark arrows show the 
direction in each image. Note the strong anti-correlation between (b,c) indicating the full magnetization reversal of the SPM islands. The differences in the intensity in (b–d) are due to a drift in the scanning height of the SOT. (e–h) Numerical simulations of Bz(x,y) 105 nm above the sample arising from randomly positioned non-overlapping SPM islands at the top and bottom surfaces of the 8 u.c. film using the measured m distribution in (j). (e) ZFC state with random magnetization orientation of SPM islands along x and y easy axes. Scale bar is 200 nm. (f–h) Same as (e) with all the moments oriented with equal probability either along −x or −y (f), along +x or +y (g), and only along +x (h) directions. (i) x−y locations of the SPM reversal events with the colour referring to the field 
at which the reversal occurred (see Supplementary Movie 4). (j) Histogram of the magnetic moments m of the SPM reversals in (i) and the corresponding island diameters D (top axis) using Ne=2 u.c. (k) Cumulative magnetic moment M versus applied field (red) attained by vectorial summation of all the reversal events m after sweeping the field from large negative value. The dashed line shows corresponding schematic reconstruction of M(H). Global M(H) measurement (blue, after subtraction of bare STO M(H)) normalized by the total sample area relative to the imaged area.
