Using coherent x-ray speckle metrology, we have measured the influence of disorder on major loop return point memory (RPM) and complementary point memory (CPM) for a series of perpendicular anisotropy Co/Pt multilayer films. In the low disorder limit, the domain structures show no memory with field cycling--no RPM and no CPM. With increasing disorder, we observe the onset and the saturation of both the RPM and the CPM. These results provide the first direct ensemble-sensitive experimental study of the effects of varying disorder on microscopic magnetic memory and are compared against the predictions of existing theories.

The chemical and electronic-structure profiles of magnetic tunnel junction ͑MTJ͒ La 0.7 Sr 0.3 MnO 3 / SrTiO 3 ͑LSMO/STO͒ superlattices have been quantitatively determined via soft and hard x-ray standing-wave excited photoemission, x-ray absorption and x-ray reflectivity, in conjunction with x-ray optical and core-hole multiplet theoretical modeling. Epitaxial superlattice samples consisting of 48 and 120 bilayers of LSMO and STO, each nominally four unit cells thick, and still exhibiting LSMO ferromagnetism, were studied. By varying the incidence angle around the superlattice Bragg condition, the standing wave was moved vertically through the interfaces. By comparing experiment to x-ray optical calculations, the detailed chemical profile of the superlattice and its interfaces was quantitatively derived with angstrom precision. The multilayers were found to have a small ϳ6% change in periodicity from top to bottom. Interface compositional mixing or roughness over ϳ6 Å was also found, as well as a significant change in the soft x-ray optical coefficients of LSMO near the interface. The soft x-ray photoemission data exhibit a shift in the position of the Mn 3p peak near the interface, which is not observed for Mn 3s. Combined with core-hole multiplet theory incorporating Jahn-Teller distortion, these results indicate a change in the Mn bonding state near the LSMO/STO interface. Our results thus further clarify the reduced ͑MTJ͒ performance of LSMO/STO compared to ideal theoretical expectations.

Soft x-ray standing waves produced by a multilayer interference substrate add depth sensitivity to magnetic circular dichroism to resolve changes in Co magnetism across a 1 nm distance from the Co center to the Co-on-Pd interface of a Pd/Co/Pd trilayer with an in-plane magnetization. Large enhancements of the number of Co d holes, and of in-plane orbital and spin magnetic moments, are strongly localized at a thin, chemically modified interface layer. These results provide new insight into magnetic anisotropy at interfaces, and suggest a broad applicability of such standing wave measurements to interface magnetism studies.

The CoFeB/MgO system shows promise as a magnetic tunnel junction with perpendicular magnetization and low critical current densities for spin-torque driven magnetization switching. The distribution of B after annealing is believed to be critical to performance. We have studied the distribution of B in a Ta/Co0.2Fe0.6B0.2/MgO sample annealed at 300 °C for 1 h with standing-wave hard x-ray photoemission spectroscopy (SW-HXPS). Comparing experimental rocking curve data to x-ray optical calculations indicates diffusion of 19.5% of the B uniformly into the MgO and of 23.5% into a thin TaB interface layer. SW-HXPS is effective for probing depth distributions in such spintronic structures.