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55 Mn NMR experiments were carried out at 1.3-4.2 K on six samples of lanthanum manganites, with a hole doping concentration ranging from the antiferromagnetic-insulator to the ferromagnetic-conductor region of the phase diagram. The dependence of the resonance frequencies on external fields is either as expected for ferromagnets ͑FM͒ or for antiferromagnets ͑AF͒. No indication of a canted phase could be detected. FM and AF resonances were found to coexist in all samples and are grouped in three broad bands, whose frequencies do not depend in first order on hole concentration. Strong evidence of interaction between AF and FM regions was provided by longitudinal relaxation experiments in several samples. An explanation of this behavior is offered in terms of intrinsic phase separation of the holes into FM microdomains. We determine the 55 Mn hyperfine coupling to be isotropic in all cases, with Aϭ6.2 T/ B for the on-site term in the AF domains.

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We have measured the transverse field muon spin precession in the flux-lattice (FL) state of the twogap superconductor MgB 2 and of the electron doped compounds Mg 1ÿx Al x B 2 in magnetic fields up to 2.8 T. We show the effect of the two gaps on the internal field distribution in the FL, from which we determine two coherence length parameters and the doping dependence of the London penetration depth. This is an independent determination of the complex vortex structure already suggested by the STM observation of large vortices in a MgB 2 single crystal. Our data agree quantitatively with STM and we thus validate a new phenomenological model for the internal fields.