Field-dependent magnetic domain structure in antiferromagnetically coupled multilayers by polarized neutron scattering

Abstract

We study the magnetic structure of antiferromagnetically ͑AF͒ coupled Co/ Cu multilayers ͑MLs͒ with 10 or 40 bilayers under the influence of an external field by polarized neutron scattering in specular and off-specular geometry. We observe in the spin-flip channels off-specular intensities around the 1 2 -order Bragg position. Based on simulations of the measured data within the distorted-wave Born approximation we find vertically correlated domains, and their domain size evolves for a sufficiently large number of bilayers along the ML stack. Small domains most likely at the top and large domains presumably at the bottom coexist within a single ML. The small domains gradually get aligned with the applied field direction around 0.5 kOe, whereas the bigger domains remain AF coupled up to 3.0 kOe, which is well above the apparent saturation field measured by conventional magnetometry methods. Moreover, we observe a double-peak structure at the 1 2 -order position for the MLs with ten as well as 40 bilayers.

Depth-resolved investigation of the lateral magnetic correlations in a gradient nanocrystalline multilayer

“…For a good interpretation of the measured data it is therefore important to measure both specular and off-specular signals. 13,32,33 …”

“…30,31 At grazing incidence, the lengths obtained by projecting the coherence volume of the neutron beam on the sample surface may become rather large ͑up to the mm range͒ but usually remain smaller than the sample surface and therefore have to be compared with the lengths of lateral correlations present in the sample. This can have important consequences for the interpretation and simulation of specular reflectivity 20 and off-specular scattering, 13,32,33 as explained in Sec. II A.…”

Diffusion des neutrons polarisés en incidence rasante

“…Le but de l'étude était de déterminer la structure micromagnétique des couches de Co en fonction du champ magnétique appliqué perpendiculaire à l'axe de facile aimantation (Figure 11, en haut à droite) et de la corréler aux mesures macroscopiques de cycle d'aimantation et de magnétorésistance géante [27].…”

“…Ceci est dû au fait que le signal mesuré à cette position est purement d'origine diffusion en incidence rasante. [27]. Sont représentés en haut à gauche la géométrie instrumentale, au milieu en bas une simulation de la diffusion hors spéculaire dans l'approximation de Born de l'onde distordue, et à droite le modèle micromagnétique déduit.…”

“…Les mesures de diffusion diffuse sont simulées dans l'approximation de Born de l'onde distordue [27,28]. Une telle simulation est représentée sur la Figure 11 (au milieu en bas).…”