Magnetic filaments in resistive manganites.

The magnetic phase separation in single crystals of the Pr0.67Ca0.33MnO3 manganites is studied using polarized small angle neutron scattering. The measured spectra give a fractal dimension consistent with a configuration in ferromagnetic filaments of nanometric diameter. We argue here that localized charge carriers hop in a random walk fashion mediating a ferromagnetic "hopping exchange" which coexists with superexchange to create the filamentary phase separation. The arguments for this physical picture are validated by Monte Carlo simulations, where magnetism and transport are treated in a self-consistent manner.

[Rapidly progressive dementia caused by tumor microembolism in the central nervous system]. / Demencia de evolución rapidamente progresiva producida por microembolias tumorales en el sistema nervioso central.

Brain tumoral microembolism is a very unusual etiology of cerebral vascular disease in patients with cancer. The clinical course is characterized by diffuse encefalopathy with associated neurologic deficits. We report a 72-year-old male patient, who developed rapidly progressive dementia associated with diffuse myoclonic jerks, without neurologic deficit, whose brain biopsy showed microscopic emboli of adenocarcinoma of unknown origin in capillary vessels. We did not find metastasis in other organs. We suggest that this entity should be included in the differential diagnoses of the subacute dementias.