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Structural relaxation in a ${\mathrm{Sr}}_{2}{\mathrm{CrReO}}_{6}$ epitaxial film, which exhibits strong spin-orbit coupling, leads to depth-dependent magnetism. We combine two depth-resolved synchrotron x-ray techniques---two-dimensional reciprocal space mapping and x-ray magnetic circular dichroism---to quantitatively determine this effect. An 800-nm-thick film of ${\mathrm{Sr}}_{2}{\mathrm{CrReO}}_{6}$, grown with tensile epitaxial strain on ${\mathrm{SrCr}}_{0.5}{\mathrm{Nb}}_{0.5}{\mathrm{O}}_{3}(225\phantom{\rule{0.16em}{0ex}}\mathrm{nm})/{\text{(LaAlO}}_{3}{)}_{0.3}({\text{Sr}}_{2}{\mathrm{AlTaO}}_{6}{)}_{0.7}$, relaxes away from the ${\mathrm{Sr}}_{2}{\mathrm{CrReO}}_{6}{\text{/SrCr}}_{0.5}{\mathrm{Nb}}_{0.5}{\mathrm{O}}_{3}$ interface to its bulk lattice parameters, with much of the film being fully relaxed. Grazing incidence x-ray diffraction of the film elucidates the in-plane strain relaxation near the film-substrate interface, while depth-resolved x-ray magnetic circular dichroism at the Re L edge reveals the magnetic contributions of the Re site. The smooth relaxation of the film near the interface correlates with changes in the magnetic anisotropy. This provides a systematic and powerful way to probe the depth-varying structural and magnetic properties of a complex oxide with synchrotron-source x-ray techniques.

We have determined the depth-resolved magnetization structures of a series of highly ordered Sr$_{2}$CrReO$_{6}$ (SCRO) ferrimagnetic epitaxial films via combined studies of x-ray reflectometry, polarized neutron reflectometry and SQUID magnetometry. The SCRO films deposited directly on (LaAlO$_3$)$_{0.3}$(Sr$_2$AlTaO$_6$)$_{0.7}$ or SrTiO$_{3}$ substrates show reduced magnetization of similar width near the interfaces with the substrates, despite having different degrees of strain. When the SCRO film is deposited on a Sr$_{2}$CrNbO$_{6}$ (SCNO) double perovskite buffer layer, the width the interfacial region with reduced magnetization is reduced, agreeing with an improved Cr/Re ordering. However, the relative reduction of the magnetization averaged over the interfacial regions are comparable among the three samples. Interestingly, we found that the magnetization suppression region is wider than the Cr/Re antisite disorder region at the interface between SCRO and SCNO.

The depth profile of the intrinsic magnetic properties in an Fe/Sm-Co bilayer fabricated under nearly optimal spring-magnet conditions was determined by complementary studies of polarized neutron reflectometry and micromagnetic simulations. We found that at the Fe/Sm-Co interface the magnetic properties change gradually at the length scale of 8 nm. In this intermixed interfacial region, the saturation magnetization and magnetic anisotropy are lower and the exchange stiffness is higher than values estimated from the model based on a mixture of Fe and Sm-Co phases. Therefore, the intermixed interface yields superior exchange coupling between the Fe and Sm-Co layers, but at the cost of average magnetization., Comment: 16 pages, 6 figures and 1 table

Recent magnetometry measurements in modulation-doped La{sub 1-x}Ca{sub x}MnO{sub 3} suggested that a net magnetization extends from the ferromagnetic layers into the adjacent antiferromagnet layers. Here we test this hypothesis by polarized neutron reflectometry, which allows us to determine the depth resolved magnetization profile. From fits to the reflectivity data we find that the additional magnetization does not occur at the ferromagnetic/antiferromagnetic interfaces, but rather in a thin region of the first antiferromagnetic layer adjacent to the interface with the substrate.

A unified approach combining polarized neutron and resonant x-ray magnetic reflectometry has been applied to determine the magnetic structure in an ${[\text{Fe}(35\text{ }\text{\AA{}})/\text{Gd}(50\text{ }\text{\AA{}})]}_{5}$ multilayer as a function of temperature and magnetic field. Simultaneous self-consistent refinement of neutron and x-ray data made it possible to resolve the element-specific magnetization profile in the multilayer with unprecedented accuracy. It is shown that the small number of bilayer periods together with the asymmetric termination (Fe-top, Gd-bottom) lead to unique low-temperature magnetic phases characterized by significant twisting of Fe and Gd magnetic moments and nonuniform distribution of vectorial magnetization within Gd layers. A twisted magnetic state was found to be stable at small magnetic fields and at a low temperature of 20 K, which is well below the compensation temperature of this artificial ferrimagnetic system.

Polarized neutron reflectivity measurements of a ferromagnetic ${[{({\text{LaMnO}}_{3})}_{11.8}/{({\text{SrMnO}}_{3})}_{4.4}]}_{6}$ superlattice reveal a modulated magnetic structure with an enhanced magnetization at the interfaces where ${\text{LaMnO}}_{3}$ was deposited on ${\text{SrMnO}}_{3}$ (LMO/SMO). However, the opposite interfaces (SMO/LMO) are found to have a reduced ferromagnetic moment. The magnetic asymmetry is accompanied by a corresponding asymmetry in the lateral structural roughness of the two interfaces observed via electron microscopy, with enhanced ferromagnetism present at the interfaces that are atomically smooth over tens of nanometers. This result demonstrates that atomic-scale roughness can destabilize interfacial phases in complex oxide heterostructures.

We report on large magnetoresistance in ferromagnet/superconductor/ferromagnet trilayer structures made of ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ and ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$. We find that the shape and height of the magnetoresistance peaks are not modified when the relative orientation of current and magnetic field is changed from parallel to perpendicular. Furthermore, we find that the temperature shift of the resistance curves is independent of current and of the sweep rate of the magnetic field. These observations favor the view that the magnetoresistance phenomenon originates in the spin dependent transport of quasiparticles transmitted from the ferromagnetic electrodes into the superconductor, and rule out interpretations in terms of spontaneous vortices or anisotropic magnetoresistance of the ferromagnetic layers.

We have used complementary neutron and x-ray reflectivity techniques to examine the depth profiles of a series of as-grown and annealed Ga{sub 1-x}Mn{sub x}As thin films. A magnetization gradient is observed for two as-grown films and originates from a nonuniformity of Mn at interstitial sites, and not from local variations in Mn at Ga sites. Furthermore, we see that the depth-dependent magnetization can vary drastically among as-grown Ga{sub 1-x}Mn{sub x}As films despite being deposited under seemingly similar conditions. These results imply that the depth profile of interstitial Mn is dependent not only on annealing, but is also extremely sensitive to initial growth conditions. We observe that annealing improves the magnetization by producing a surface layer that is rich in Mn and O, indicating that the interstitial Mn migrates to the surface. Finally, we expand upon our previous neutron reflectivity study of Ga{sub 1-x}Mn{sub x}As, by showing how the depth profile of the chemical composition at the surface and through the film thickness is directly responsible for the complex magnetization profiles observed in both as-grown and annealed films.

We studied the magnetic properties of ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}∕{\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ superlattices. Magnetometry showed that with increasing ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ layer thickness the saturation magnetization per ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ layer decreases. From polarized neutron reflectometry we determined that this magnetization reduction is due to an inhomogenous magnetization depth profile arising from the suppression of magnetization near the ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}∕{\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ interface. Electron energy loss spectroscopy indicates an increased $3d$ band occupation of the Mn atoms in the ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ layers at the interface. Thus, the suppression of ferromagnetic order at the ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}∕\phantom{\rule{0.3em}{0ex}}{\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ interface is most likely due to charge transfer between the two materials.

We have studied the depth-dependent magnetic and structural properties of as-grown and optimally annealed ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ films using polarized neutron reflectometry. In addition to increasing the total magnetization, the annealing process was observed to produce a significantly more homogeneous distribution of the magnetization. This difference in the films is attributed to the redistribution of Mn at interstitial sites during the annealing process. Also, we have seen evidence of significant magnetization depletion at the surface of both as-grown and annealed films.