MOSSBAUER EFFECT OF 61Ni IN SPINEL TYPE MAGNETIC OXIDES

internes d'oxydes contenant du Nickel, de structure spinelle ou spinelle dbformee. Les champs magnetiques internes dans des oxydes contenant des ions de Nickel en site octaedrique, ont ete trouves de l'ordre de 70 a 100 kOe. Dans NiCr204, oh les ions de Nickel se trouvent sur des sites tbtrakdriques, nous avons mesurb un champ magnetique interne voisin de 450 kOe B la temperature de 1'Helium liquide. Cette valeur semble &re la plus Blevee jamais trouvee pour le 61Ni. Abstract.- The Mossbauer spectroscopy of 61Ni was effectively utilized to investigate the internal magnetic fields in Ni-containing oxides with spinel or distorted spinel structure. The internal magnetic fields in oxides with the nickel ions in octahedral site were observed to be 70-100 kOe. In NiCr204, in which nickel ions are in tetrahedral site, an inter-nal magnetic field amounting to 450 kOe was observed at liquid He temperature. This value seems to be the largest one ever observed for 61Ni. I. Introduction.- In spite of many experimentally undesirable nuclear properties, 61Ni can be a powerful probe in solid state physics as the only Mossbauer nuclide other than 57Fe in the iron group transition elements [ I, 2, 3, 41, especially in the studies o