X-ray photoelectron emission microscopy in combination with x-ray magnetic circular dichroism investigation of size effects on field-induced Néel-cap reversal

Abstract

X-ray photoelectron emission microscopy in combination with x-ray magnetic circular dichroism is used to investigate the influence of an applied magnetic field on Néel caps (i.e., surface terminations of asymmetric Bloch walls). Self-assembled micron-sized Fe(110) dots displaying a moderate distribution of size and aspect ratios serve as model objects. Investigations of remanent states after application of an applied field along the direction of Néel-cap magnetization give clear evidence for the magnetization reversal of the Néel caps around 120 mT, with a ±20 mT dispersion. No clear correlation could be found between the value of the reversal field and geometrical features of the dots.

Controlled Switching of Néel Caps in Flux-Closure Magnetic Dots

“…Besides as opposite chiralities induce dark or light fringes, respectively, the experimental images (i-viii) taken through the hysteresis demonstrate that the chirality is not affected by the switching of the NCs, neither at rising nor at decreasing field. This is consistent with XMCD-PEEM experiments where the occurrence of clockwise and anticlockwise chiralities remained similar for all applied magnetic fields and no cross correlation between the chirality and the state of the NCs could be evidenced either, within the statistical error bars [28]. Concerning the polarity of the DW core, which is detectable neither by XMCD-PEEM nor by Lorentz microscopy, we must rely only on the simulations to infer that the core of the DW remains unaffected by the switch of NCs.…”

Asymmetric Hysteresis of Néel Caps in Flux-Closure Magnetic Dots

“…We showed that in such dots the final remanent state is selected by the sign of the applied field [6]. A statistical analysis over assemblies of dots [10], [6] revealed a switching field of 120 ± 20 mT, while still ≈ 10 % of the dots did not switch at 150 mT. No correlation could be established between the value of the switching field and geometrical features of the dots such as height or vertical aspect ratio [10].…”

“…A statistical analysis over assemblies of dots [10], [6] revealed a switching field of 120 ± 20 mT, while still ≈ 10 % of the dots did not switch at 150 mT. No correlation could be established between the value of the switching field and geometrical features of the dots such as height or vertical aspect ratio [10]. In this work we shed light on these results by reporting hysteresis loops of individual dots, whereas in the previous studies the dots could not be tracked individually between the applications of magnetic field.…”

Quantitative x-ray magnetic circular dichroism mapping with high spatial resolution full-field magnetic transmission soft x-ray spectro-microscopy

“…Neel caps, i.e. in-plane rotating spins have been predicted by micromagnetic modeling in magnetite to eliminate surface poles magnetized elements [14] and have been observed recently with X-PEEM in Fe (110) dots [15].…”