Nuclear Magnetic Resonance of Paramagnetic Co₃O₄. I. Experimental Study

Abstract

Nuclear magnetic resonance of Co 59 in polycrystalline Co 3 O 4 and ZnCo 2 O 4 , and Al 27 in CoAl 2 O 4 in paramagnetic state was observed. The cobalt signal was identified with the Co 3+ ions at the octahedral sites of the spinel structure. The line shift of Co 59 in Co 3 O 4 was separated into two terms: temperature-independent and temperature-dependent ones. The temperature-independent shift (1.5%) is interpreted as the second order chemical shift due to the mixing of the low lying excited state. The temperature-dependent shift is attributed to the hyperfine coupling between the cobalt nuclear spin and the electron spins on the Co 2+ ions at the tetrahedral sites. The isotropic hyperfine coupling constant A is estimated at 13×10 -4 cm -1 . The results on ZnCo 2 O 4 and CoAl 2 O 4 give supports to the above interpretations. The line shapes were studied and the thermal relaxation time T 1 was estimated to be 1.5×10 -5 sec.