Study of domain wall propagation in nanostructured CoPt multilayers by using antisymmetric magnetoresistance

Interplay between collective pinning and artificial defects on domain wall propagation in Co/Pt multilayers

“…At low temperatures, most propagation events correspond to forward DW motion, reflecting the different areas of the right and left nucleation pads but, as temperature increases, a larger number of negative magnetoresistance peaks (corresponding to backward DW propagation) are observed. In contrast, only forward propagation events were detected in a similar experiment with a Co/Pt wire of identical geometry but without the patterned hole [16] as expected from nucleation-pad geometry. Thus, the probability of backward DW propagation can be taken as a measure of the pinning efficiency of the patterned hole.…”

“…On the contrary, only forward propagation events were detected in a similar experiment with a Co/Pt wire of identical geometry but without the patterned hole [16] as expected from nucleation pad geometry. Thus, the probability of backward DW propagation can be taken as a measure of the pinning efficiency of the patterned hole.…”

“…Co/Pt wires have been fabricated from high quality epitaxial Pt(3 nm)/[Co(0.6 nm)/Pt(1 nm)] 4 /Pt(3 nm) multilayers with perpendicular magnetic anisotropy in which magnetization reversal takes place by DW motion following rare nucleation events [8,14]. A combination of e-beam lithography and an etching process through Ar + milling [16] has been used to fabricate a 40 µm long wire of width w = 5 µm (see figure 1(a)), together with two longitudinal contact pads for current injection (labelled I L and I R in the figure) and three pairs of transverse contact pads spaced at 20 µm intervals to allow for voltage measurements (V 1 to V 6 ). In a second optical lithography step Al contacts are sputtered onto the Co/Pt voltage/current pads in order to make electrical connections into the sample.…”

“…These experiments require the design of effective local pinning centres, a careful understanding of the different sources of asymmetry present in a magnetic circuit (nucleation pads, shape and location of pinning centres) and the development of detection techniques that determine not only DW speed but also its propagation direction. Kerr microscopy has been the preferred technique for samples with in plane magnetization [6,7] but, for 0022-3727/10/305002+05$30.00 perpendicular anisotropy multilayers, the recently discovered antisymmetric magnetoresistance can provide information on DW propagation sense in a much simpler way [15,16].…”

Perpendicular magnetic anisotropy in Nd-Co alloy films nanostructured by di-block copolymer templates

“…32 Low temperature extraordinary Hall effect (EHE) has been measured in a He cryostat with a 90 kOe electromagnet in order to obtain the out-of-plane hysteresis loops of the PMA samples. 33,34 Magnetic domain structure has been characterized at room temperature by magnetic force microscopy (MFM) using a Nanotec TM system equipped with a 1 kOe electromagnet that allows us to apply in-plane variable fields. 35 Figure 3 shows the MOTKE in-plane hysteresis loops of a 52 nm Nd-Co/template sample with the magnetic field applied either along the in-plane easy axis ( Fig.…”