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Single crystals of ${\mathrm{La}}_{0.85}{\mathrm{Sr}}_{0.15}{\mathrm{MnO}}_{3\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ were prepared with various oxygen vacancies from \ensuremath{\delta}=0 to \ensuremath{\delta}=0.055. The $b$ and $c$ lattice parameters were found to increase with \ensuremath{\delta} whereas the $a$ parameter remains practically constant. The oxygen vacancies are expected to reduce the hole concentration, and therefore the Curie temperature and the electrical conductivity. However, these effects are somewhat different from those observed in the hole-doped ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ systems, owing to different lattice distortion. The lattice change of the sample is illustrated by a strong shift in the hyperfine field of ${\mathrm{Mn}}^{4+}$ ions, detected with the NMR method. The oxygen deficiency and all the above properties resulting from it were shown to be reversible.

Nuclear magnetic resonance (NMR) and low-temperature magnetization measurements are used to demonstrate antiferromagnetic (AF) coupling in molecular beam epitaxy grown (111)-oriented Co/Pt superlattices. Drastic changes in the NMR spin-echo spectra as a function of the in-plane dc magnetic-field strength provide conclusive evidence of AF interlayer coupling in these structures, consisting of 35- and 52-A Co and 18-A Pt bilayers. The structure of the Co films is mainly hcp (70%) and the coupling energy per unit area, as determined from in-plane magnetization loops is found to range up to 1 erg/cm[sup 2].

NMR spin-echo and magnetization measurements performed on a MBE-grown, (110)-oriented Co/Pt superlattice reveal a strong in-plane, uniaxial magnetic anisotropy. This is due to large tensile strain exerted from the Pt lattice onto the Co layers, which leads to an orthorhombic distortion of the Co lattice. The orthorhombic distortion is also reflected in an anisotropy of the hyperfine field detected with the NMR method. This suggests that the magnetic anisotropy is correlated with an anisotropy of the orbital magnetic moments in these structures.

We report investigations on the structure and the magnetic properties of (${\mathrm{CH}}_{3}$${)}_{4}$NNi(${\mathrm{NO}}_{2}$${)}_{3}$. From extended x-ray-absorption fine structure and x-ray-diffraction experiments, we show that (${\mathrm{CH}}_{3}$${)}_{4}$NNi(${\mathrm{NO}}_{2}$${)}_{3}$ has a chainlike structure of Ni(II) ions coupled via three ${\mathrm{NO}}_{2}$ anions. High-temperature susceptibility is consistent with one-dimensional antiferromagnetism with J/k=-12 K and g=2.25. Below 10 K, a strong decrease of susceptibility and proton relaxation rate is observed, in agreement with the Haldane prediction of a singlet ground state for the S=1, one-dimensional Heisenberg antiferromagnet. From the magnetization-versus-field data at low temperature, the Haldane gap is estimated to 4.5 K, close to the expected value 0.41 \ensuremath{\Vert}J\ensuremath{\Vert} for the S=1, one-dimensional Heisenberg antiferromagnet.

Les resultats demontrent l'utilite de la resonance magnetique pour l'etude de la structure interfaciale dans des superreseaux a base de cobalt. Les satellites hyperfins n'identifient que des atomes Co interfaciaux avec trois plus proches voisins Cu. Ceci indique la presence d'interfaces atomiquement abruptes. Les couches de Co ont une symetrie d'empilement cubique a faces centrees

The hyperfine fields at the nuclei of ${\mathrm{Cd}}^{2+}$, ${\mathrm{Ga}}^{3+}$, and ${\mathrm{In}}^{3+}$ ions in the substituted ferromagnetic spinel ${\mathrm{CdCr}}_{2}$${\mathrm{S}}_{4}$ have been measured by the spin-echo method at liquid-helium temperature. The impurity, when located at the B site, produces a large shift in the resonance frequency of the ${\mathrm{Cd}}^{2+}$ ions nearest to it, and shows an anomalous field dependence of its own resonance frequency. A well-defined canted spin structure was then deduced from these NMR data. Such a structure was reproduced by simulation on a system of N=1185 spins, taking into account all positive nearest-neighbor and negative third-neighbor pair interactions plus local interactions around the impurity. The simulation results showed that these local interactions must be introduced in order to create the canted spin structure, and are much greater than the original ones. This strong effect was ascribed to the superexchange interaction via the impurity s valence electron whose spin density, as deduced from the hyperfine interaction, is unusually high.

Ferromagnetic resonance measurements in Co films of 11.3, 20, and 80 A\r{} thickness sandwiched by Au have been made as a function of the dc magnetic field orientation in a plane perpendicular to the film. These polycrystalline films were measured to have the hcp structure with the c axis perpendicular to the film plane within a few degrees. The experimental results are well explained by a theoretical model where an axial magnetic anisotropy up to the second-order term is included.

Proton NMR in nonsuperconducting GdBa{sub 2}Cu{sub 3}O{sub 7}H{sub 1.55} was measured at liquid-helium temperature by a spin-echo method. The negative shift of the resonance spectrum was found to be proportional to the dc magnetic field. This shift is shown to arise from the demagnetizing field due to a canted spin structure. The Gd exchange parameter is estimated to be {ital J}{approx equal}0.05 K, showing that the exchange energy is higher than the dipole one. Hydrogen doping has no effect on the gadolinium ordering temperature.

The magnetization of the mixed spinel Cd${\mathrm{Cr}}_{1.8}$${\mathrm{In}}_{0.2}$${\mathrm{S}}_{4}$ has been measured at 4 K in a dc magnetic field up to 5 T. The monotonic increase of the magnetization with external field revealed the randomly ferromagnetic behavior of the system. The simulation on a subcrystal containing $1372B$ sites, using the previously reported exchange parameters, is consistent with experiment.