NMR-STUDY ON THE SUPERTRANSFERRED HYPERFINE MAGNETIC-FIELD AT MN-55 IN FERROMAGNETIC PEROVSKITES LA(CO1-XMGX)(0.5)MN0.5O3

Magnetic properties and the hyperfine magnetic fields at Mn-55 in ferromagnetic oxides La(Co1-x2+Mgx2+)(0.5)Mn0.54+O3 (0 less than or equal to x less than or equal to 0.4) are studied. The exchange integral, J, for the superexchange interaction between neighboring Mn4+ and Co2+ ions is found to be + 15.3 K in magnitude. Mn-55 NMR spectra, composed of several equidistantly separated peaks, are interpreted as each peak being the signal associated with Mn4+ surrounded by a specific number of Co2+ ions. The supertransferred hyperfine magnetic field, H-STHF, at Mn-55 from each neighboring Co2+ ion is found to be + 5.0 kOe, which is considerably smaller than that (+ 6.3 kOe) from Ni2+ in a similar oxide system La(Ni1-xMgx)(0.5)Mn0.5O3 On the other hand, the hyperfine magnetic field (- 296 kOe) originating from 3d magnetic moment of Mn4+ is virtually the same in both systems. The values of J and H-STHF are discussed in relation with the spin density in 2p(sigma), orbitals of the oxygen ions.