NMR Study of Internal Field of Trivalent Diamagnetic Cations in Nickel Ferrite

Large internal fields of Al 3+ , Ga 3+ substituted in NiFe 2 O 4 were observed with spin echo method at 4.2 K. The fields increase rapidly with the atomic number. Contributions to the field by the A - A and B - B interactions are negligibly small in comparison with the A - B interaction. Transferred fields of these cations from Fe 3+ and Ni 2+ were separated. Direction of the field of In 3+ on the A -site is parallel to the total magnetization. The results were analyzed with a simple molecular orbital method. Polarized valence orbital of the diamagnetic cations induces the field predominantly but distorted outermost closed shell also contributes considerably to the field through cross terms. Electron transfers from one 2p and 2s orbitals of O 2- to the cations on the A -site are 4∼6% and 0.1∼0.5% respectively and those from one 2p orbital of O 2- to the cations on the B -site are 10∼13%.