NMR Study on the Supertransferred Hyperfine Magnetic Field at⁵⁵Mn in Ferromagnetic Perovskites La(Co_1-<i>x</i>Mg_<i>x</i>)_0.5Mn_0.5O₃

Abstract

Magnetic properties and the hyperfine magnetic fields at 55 Mn in ferromagnetic oxides La(Co 2+ 1- x Mg x 2+ ) 0.5 Mn 0.5 4+ O 3 (0≤ x ≤0.4) are studied. The exchange integral, J , for the superexchange interaction between neighboring Mn 4+ and Co 2+ ions is found to be +15.3 K in magnitude. 55 Mn NMR spectra, composed of several equidistantly separated peaks, are interpreted as each peak being the signal associated with Mn 4+ surrounded by a specific number of Co 2+ ions. The supertransferred hyperfine magnetic field, H STHF , at 55 Mn from each neighboring Co 2+ ion is found to be +5.0 kOe, which is considerably smaller than that (+6.3 kOe) from Ni 2+ in a similar oxide system La(Ni 1- x Mg x ) 0.5 Mn 0.5 O 3 . On the other hand, the hyperfine magnetic field (-296 kOe) originating from 3 d magnetic moment of Mn 4+ is virtually the same in both systems. The values of J and H STHF are discussed in relation with the spin density in 2 p σ orbitals of the oxygen ions.