55 Mn NMR experiments have been performed at 4.2 K on a series of Mn5(Ge1-xSix)3 5 (Ge 1- x Si x ) 3 epitaxial films (0 0 x 0.55) . 55 ) to investigate changes introduced by silicon when it replaces germanium in a hexagonal Mn5Ge3 5 Ge 3 crystal lattice. The Si/Ge substitution was found to reduce the magnetic moment on manganese located in the 6(g) sublattice creating a new population of manganese atoms with distinctly lower magnetic moment. This effect is attributed to the orbital overlay due to a lattice distortion introduced by Si. Interestingly, these modified Mn sites retain the orbital moment practically unaltered. The amount of new manganese environments in the 6(g) sublattice coincides with a probability of Mn having two Si neighbors as first neighbors. Mn atoms located in the 4(d) sublattice are not significantly affected by the Si substitution in the studied concentration range.

55Mn NMR experiments have been performed at 4.2 K on a series of Mn5(Ge1−xSix)3 epitaxial films (0⩽x⩽0.55) to investigate changes introduced by silicon when it replaces germanium in a hexagonal Mn5Ge3 crystal lattice. The Si/Ge substitution was found to reduce the magnetic moment on manganese located in the 6 g sublattice creating a new population of manganese atoms with distinctly lower magnetic moment. This effect is attributed to the modified exchange interactions due to a lattice distortion introduced by Si. Interestingly, these modified Mn sites retain the orbital moment practically unaltered. The amount of new manganese environments in the 6 g sublattice coincides with a probability of Mn having two Si neighbors as first neighbors. Mn atoms located in the 4d sublattice are not significantly affected by the Si substitution in the studied concentration range.

55Mn NMR experiments have been performed at 4.2 K on a series of Mn5(Ge1−xSix)3 epitaxial films (0⩽x⩽0.55) to investigate changes introduced by silicon when it replaces germanium in a hexagonal Mn5Ge3 crystal lattice. The Si/Ge substitution was found to reduce the magnetic moment on manganese located in the 6 g sublattice creating a new population of manganese atoms with distinctly lower magnetic moment. This effect is attributed to the modified exchange interactions due to a lattice distortion introduced by Si. Interestingly, these modified Mn sites retain the orbital moment practically unaltered. The amount of new manganese environments in the 6 g sublattice coincides with a probability of Mn having two Si neighbors as first neighbors. Mn atoms located in the 4d sublattice are not significantly affected by the Si substitution in the studied concentration range.

Nanolaminated Mn2GaC epitaxial films crystallizing in the hexagonal structure belong to the family of MAX phase compounds and display complex magnetic interactions. While the critical temperature of the order-disorder transition is 507 K, at around 214 K this compound undergoes a first-order phase transition with the magnetic structure below the transition point not being fully resolved. Previous studies indicated a noncollinear spin arrangement, but a specific magnetic structure could not be defined. In this work we present the results of 69Ga, 71Ga, and 55Mn NMR experiments performed at 4.2 K in an external in-plane magnetic field up to 1 T. The in-depth analysis of the experimental results shows a helical magnetic structure consisting of the ferromagnetically coupled Mn-C-Mn slabs that are twisted across the Ga layer by 167.2 degrees with respect to the next Mn-C-Mn slab. As a result, the magnetic structure presents a spiral propagating along the out-of-plane direction (hexagonal c axis) with a pitch of around 14 lattice constants.

Zero-field NMR investigations on the 69Ga, 71Ga, and 55Mn nuclei have been performed at 4.2 K on a 100 nm thick epitaxial Mn2GaC(0001) MAX phase film grown on a MgO(111) substrate. This nano-laminated structure consists of ferromagnetic Mn-C-Mn stacks interleaved with monolayers of gallium. A resolved quadrupolar structure of the observed gallium resonances is a fingerprint of a well-defined crystal field confirming high crystal quality. The nuclei of non-magnetic gallium atoms are shown to experience the transferred hyperfine magnetic field of 15.75 T (& PLUSMN;0.05 T), which is due to polarization of their 4s electron shell by the magnetic moments of manganese neighbors, evidencing the presence of an uncompensated ferromagnetic moment within the manganese sublattice. The average magnetic moment of manganese was found to be around 2 & mu;B, strongly contrasting with the reported remnant magnetization of only 0.3 & mu;B. Moreover, the 55Mn NMR spectrum in-dicates the presence of magnetically non-equivalent manganese sites within this structure. The observed features of the 69,71Ga and 55Mn NMR spectra cannot be reconciled with any of the hitherto proposed collinear ar-rangements of manganese moments and suggest their non-collinear arrangement across a gallium layer. Nevertheless a more advanced study is required to elucidate the detailed nature of magnetic structure in this material.

Local magnetic properties of the ${\mathrm{Mn}}_{5}{\mathrm{Ge}}_{3}{\mathrm{C}}_{x}$(001) epitaxial films grown on Ge(111) with a nominal carbon concentration $0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.85$ have been studied by means of $^{55}\mathrm{Mn}$ nuclear magnetic resonance (NMR). The NMR spectra were recorded from the demagnetized films and from the films fully magnetized along the $c$ direction as well as in the hexagonal $c$ plane. The data unambiguously show a synchronized carbon penetration of the crystal lattice ($D{8}_{8}$ structure, Nowotny phase, space group $P{6}_{3}/mcm$), occupying every second $2(b)$ void located within the chain of $\mathrm{Mn}[6(g)]$ octahedra and setting the limit for the carbon uptake into the ${\mathrm{Mn}}_{5}{\mathrm{Ge}}_{3}$ lattice at $x=0.5$. Moreover, the NMR data indicate that the chains of carbon-filled voids are correlated also in plane. Eventually, for the end concentration of $x=0.5$, a highly ordered superstructure is proposed, responsible for the observed two magnetically inequivalent positions within the $\mathrm{Mn}[4(d)]$ sublattice.

Local magnetic properties of the Mn5Ge3Cx (001) epitaxial films grown on Ge(111) with a nominal carbon concentration 0 <= x <= 0.85 have been studied by means of Mn-55 nuclear magnetic resonance (NMR). The NMR spectra were recorded from the demagnetized films and from the films fully magnetized along the c direction as well as in the hexagonal c plane. The data unambiguously show a synchronized carbon penetration of the crystal lattice (D8(8) structure, Nowotny phase, space group P6(3)/mcm), occupying every second 2(b) void located within the chain of Mn[6(g)] octahedra and setting the limit for the carbon uptake into the Mn5Ge3 lattice at x = 0.5. Moreover, the NMR data indicate that the chains of carbon-filled voids are correlated also in plane. Eventually, for the end concentration of x = 0.5, a highly ordered superstructure is proposed, responsible for the observed two magnetically inequivalent positions within the Mn[4(d)] sublattice.

Mn-55 NMR was used to investigate the effect of carbon doping on the local magnetic anisotropy in Mn5Ge3 epitaxial films (space-group P6(3)/mcm). It was found that carbon enters interstitially in the vicinity of the 6(g) crystallographic positions, occupying the 2(b) octahedral voids. The magnetic properties of the Mn atoms located in the corners of a host octahedron are strongly modified by the presence of carbon. Their magnetic moment is reduced by 0.7 mu(B) with respect to the pristine Mn5Ge3 film and the anisotropy of their orbital moment, measured as a difference between its value along the hexagonal c direction and on the c plane is reduced to 0.058 mu(B), whereas, in the pristine Mn5Ge3 films, it oscillated every 60 degrees between 0.151 mu(B) and 0. These changes are responsible for a significant decrease in magnetocrystalline anisotropy, which was reported to drop by an order of magnitude upon doping the Mn5Ge3 films with carbon.

Mn-55 NMR was used to perform the atomic-scale study of the anisotropic properties of Mn5Ge3/Ge(111) epitaxial films with thicknesses between 9 and 300 nm. The NMR spectra have been recorded as a function of strong external magnetic field applied in the film plane and perpendicular to it. Two Mn-55 NMR resonances have been observed, corresponding to the two manganese sites 4d and 6g, in the hexagonal D8(8) structure; in zero field their frequency is centered around 207.5 and 428 MHz, respectively. The anisotropy of 55Mn hyperfine fields between the hexagonal c direction and the c plane at both Mn sites was evidenced and attributed to the anisotropic term due to the unquenched Mn orbital momentum. The anisotropy of the orbital contribution to hyperfine fields was determined as 1.52 T in the 4d site and up to 2.77 T in the 6g site. The 4d site reveals a quadrupolar interaction due to the strong electric field gradient: V-zz = 5.3 x 10(19) V/m(2) in this site, which is shown to be oriented along the hexagonal c axis.

Extensive X-band and Q-band FMR experiments have been performed in the Mn5Ge3 epitaxial films with thicknesses varying between 4.5 and 68 nm. FMR signals were recorded in the temperature range between 15 and 295 K, at different orientations of magnetic field with respect to the film plane. In addition to the acoustic FMR mode with well defined resonance field, originating from inside the magnetic domains, a broad absorption line has been observed at low fields and attributed to the unresolved spectrum of FMR modes having the origin in flux closure caps. The FMR results have been discussed in the context of the domain structure computed with the use of OOMMF micromagnetic calculations and giving good agreement with the experimental hysteresis curves. From the Q-band experiments, where the FMR signal is observed in the magnetically saturated sample, the uniaxial anisotropy constant in films with different thicknesses has been determined as a function of temperature. This FMR study provides the evidence that the strong uniaxial anisotropy observed in epitaxial thin films of Mn5Ge3 leads to the formation of a stripe domain structure above 25 nm, in agreement with the published reports on magnetization studies in these films. It also eliminates a possible confusion that may arise from previously published FMR studies on films grown with the same method, which led their authors to conclude that the shape anisotropy can force the magnetization to the in-plane orientation in this thickness range and even above it.

Mixed-valence manganites La(1-x)A(x)MnO(3) (A = Sr, Ca) with x approximate to 0.5 can be driven from a ferromagnetic-metallic to an antiferromagnetic-insulating state by a small modification (Delta x) of the carrier density (Delta x/x < 1). For this reason, these oxides have received renewed attention due to their potentially advantageous integration in ferroelectric tunnel junctions of adjustable tunnel barrier width. Interestingly, in thin films, epitaxial strain can modify the electronic and magnetic ground state strongly affecting their magnetotransport properties. Here we exploit the extreme sensitivity of linearly and circularly polarized x-ray absorption to orbital anisotropy and magnetic ordering to explore the role of structural distortions and electronic bandwidth on the orbital occupancy and spin ordering of Mn 3d states in La(0.5)A(0.5)MnO(3) films under various strain states. Mn-55 NMR experiments are used to get information about the electronic and magnetic phase separation and orbital ordering occurring in these films. These results combined with the corresponding structural, magnetic, and electrical characterization allow us to map the strain-dependent orbital and magnetic phase diagrams of half-doped manganites and its dependence on the electronic bandwidth.

Nuclear magnetic resonance (NMR) is utilized to map the hyperfine fields acting on 55Mn nuclei of La2/3Sr1/3MnO3 (LSMO) epitaxial thin films. In contrast to early thoughts, we show that phase separation (PS) in LSMO is not restricted to an interface‐related dead‐layer only a few nm thick. Instead, it propagates much deeper into the films, thus signalling different origins for the PS. These results indicate that both, surfaces and defects contribute to promote distinguishable PS effects. This view has been confirmed by detailed 55Mn NMR analysis of LSMO films where engineered bulk‐like defects have been created by appropriate irradiation by energetic He+ ions. Moreover, from the analysis of the restoring fields sensed by the spins of the 55Mn nuclei, we infer two sources of magnetic anisotropy. More specifically, a surface magnetic anisotropy –linked to the interfacial dead layer– is predominant for ultrathin samples (t < 10 nm), whereas structural film relaxation, provides a second mechanism for anisotropy. These findings provide guidelines for the growth of electric and magnetic homogeneous manganite films.

Oxygen implantation in ferromagnetic Co thin films is shown to be an advantageous route to improving the magnetic properties of Co-CoO systems by forming multiple nanoscaled ferromagnetic/antiferromagnetic interfaces homogeneously distributed throughout the layer. By properly designing the implantation conditions (energy and fluence) and the structure of the films (capping, buffer, and Co layer thickness), relatively uniform O profiles across the Co layer can be achieved using a single-energy ion implantation approach. This optimized configuration results in enhanced exchange bias loop shifts, improved loop homogeneity, increased blocking temperature, reduced relative training effects and increased retained remanence in the trained state with respect to both Co/CoO bilayers and O-implanted Co films with a Gaussian-like O depth profile. This underlines the great potential of ion implantation to tailor the magnetic properties by controllably modifying the local microstructure through tailored implantation profiles.

A systematic Co-59 NMR study has been carried out at 4.2 K in a series of quaternary Co2FeAl1-xSix polycrystalline bulk Heusler alloys ( x = 0, 0.3, 0.5, 0.7, 1). It was shown that the effect of Si substitution consists in a significant modification of Co-59 hyperfine field and that this modification is mainly due to the contribution from s valence electron polarization, suggesting a shift of the Fermi energy level inside the half-metallic gap. This observation supports the theoretical predictions that the Fermi-level position in Co(2)FeZ Heusler alloys can be effectively tuned by varying the composition of the Z sublattice.

A systematic ${}^{59}$Co NMR study has been carried out at 4.2 K in a series of quaternary Co${}_{2}$FeAl${}_{1\ensuremath{-}x}$Si${}_{x}$ polycrystalline bulk Heusler alloys ($x$ = 0, 0.3, 0.5, 0.7, 1). It was shown that the effect of Si substitution consists in a significant modification of ${}^{59}$Co hyperfine field and that this modification is mainly due to the contribution from $s$ valence electron polarization, suggesting a shift of the Fermi energy level inside the half-metallic gap. This observation supports the theoretical predictions that the Fermi-level position in Co${}_{2}$Fe$Z$ Heusler alloys can be effectively tuned by varying the composition of the $Z$ sublattice.

Owing to the sensitivity of the hyperfine field to the topological and chemical environment of the probe nuclei, NMR spectra can be considered as histograms of the short range order ruling the structure of the material under investigation. Complementary to diffraction techniques this gives a local insight on the structure in the direct space. We review recent structural investigations of cobalt layers imbedded in Co/X multilayers and particularly of buried interfaces. Special attention has been given to the way intermixing takes place at the interfaces as its influence on the multilayer properties may be of considerable importance. Co/Cu multilayers, a case of weakly miscible elements, have been specially investigated owing to their GMR properties. But also cases of solid solution forming elements (Co/Ru or Co/Cr) or compound forming elements (Co/Fe) have been thoroughly studied. The latter case, which shows a stabilization of a bcc Co phase, will be discussed against the bulk alloy phase diagram.

The local structures around Co atoms in Co2FeSi1-xAlx (x=0, 0.5, and 1.0) Heusler alloys have been investigated using Co-59 NMR spin-echo method and their effect on the tunneling magnetoresistance for the junctions using Co2FeSi0.5Al0.5 electrodes has been discussed. The Co-59 NMR spectra of the Heusler alloys are extremely sensitive to the site disorder and clearly distinguish among the A2, B2, and L2(1) structures providing quantitative information on the amount of disorder. The tunnel magnetoresistance for the junctions is demonstrated to be sensitive to the site disorder in Co2FeSi0.5Al0.5 electrodes.

orientations I. C. Infante, F. Sánchez, J. Fontcuberta, S. Estradé, F. Peiró, J. Arbiol, M. Wojcik, and E. Jedryka Institut de Ciència de Materials de Barcelona-CSIC, Campus UAB, 08193 Bellaterra, Catalonia, Spain EME/CeRMAE/IN2UB, Dept. d’Electrònica, Universitat de Barcelona, 08028 Barcelona, Catalonia, Spain TEM-MAT, Serveis Cientificotècnics, Universitat de Barcelona, 08028 Barcelona, Catalonia, Spain Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02 668 Warszawa, Poland

We report on the study of the structural, magnetic, and electronic properties of SrTiO3 capped La2∕3Ca1∕3MnO3 electrodes grown on (001) and (110) SrTiO3 substrates. Magnetic properties of the (001) and (110) capped electrodes evolve differently when the capping layer thickness increases, revealing a reduction of the saturation magnetization for the (001) ones. Electronic properties are studied combining Mn55 nuclear magnetic resonance (NMR) and x-ray photoemission spectroscopy (XPS). NMR experiments highlight that electronic phase separation in the (001) electrodes is enhanced by the presence of the SrTiO3 capping layer and XPS measurements show that the electronic state of interfacial Mn ions from (001) electrode is more sensitive to the capping layer.