Hyperfine Magnetic Field at ^<55>Mn in Ferromagnetic Perovskites REMn_<0.5>(Ni_<1-x>Mg_x)_<0.5>O_3 with RE=La,Pr,Nd, and Eu : RE Dependence of Supertransferred Hyperfine Interaction(Condensed matter: electronic structure and electrical, magnetic, and opti

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The hyperfine magnetic field at ^<55>Mn in ferromagnetically ordered double perovskites of the form REMn_<0.5>(Ni_<1-x>Mg_x)_<0.5>O_3 with RE=La, Pr, Nd, and Eu were measured by NMR at 1.8K. The hyperfine magnetic field H_<HF, Mn^<4+>>, which arises from (3dε)^3 unpaired electrons in Mn^<4+> to which ^<55>Mn belongs, is -294.5kOe independent of RE species. On the other hand, H_<STHF> supertransferred from 3d_<3z^2-r^2>unpaired electrons in the neighboring Ni^<2+> ions decreases as RE goes from La (+35.8kOe) to Eu (+20.1kOe). The RE dependence arises from the reduction in the covalency of the Mn^<4+>_-O^<2-> and Ni^<2+>_-O^<2-> bonds as RE goes from La to Eu, as well as from the cos^2θ-type bond angle dependence of the STHF interaction. With the RE dependence of covalency determined from H_<STHF>, the superexchange interaction between Mn^<4+> and Ni^<2+> depending on RE in the present system has been well interpreted.
社団法人日本物理学会の論文
2008-09-15