Effect of Frustrated Exchange Interactions and Spin-half Impurity on the Electronic Structure of Strongly Correlated NiFe2O4

Kodam Ugendar1,§ , S. Samanta2,§ , Sudhendra Rayaprol3 , V. Siruguri3 , G. Markandeyulu1 , B. R. K. Nanda2,?

1 Advanced Magnetic Materials Laboratory, Department of Physics, Indian Institute of Technology Madras, Chennai 600 036, India

2Condensed Matter Theory and Computational Lab, Department of Physics, Indian Institute of Technology Madras, Chennai 600 036, India∗ and

3 UGC-DAE Consortium for Scientific Research, Mumbai center, Bhabha Atomic Research Centre, Trombay, Mumbai - 400 085, India


Abstract:

Spin-polarized density functional calculations, magnetization, and neutron diffraction measurements are carried out to investigate the magnetic exchange interactions and strong correlation effects in Yb substituted inverse spinel nickel ferrite. In the pristine form, the compound is found to be a mixed insulator under the Zaanen-Sawtazsky-Allen classification scheme as it features both charge transfer and Mott insulator mechanism. Estimation of magnetic exchange couplings reveals that both octahedral-octahedral and octahedral-tetrahedral spin-spin interactions are antiferromagnetic which is typical of a spin-frustrated triangular lattice. However, the latter is dominant compared to the former leading to a forced parallel alignment of the spins at the octahedral site which is in agreement with the results of neutron diffraction measurements. The substituent Yb is found to be settled in +3 charge state, as confirmed from the XPS measurements, to behave like a spin-half impurity carried by the localized fz(x2−y2) orbital. The impurity f spin significantly weakens the antiferromagnetic coupling with the spins at the tetrahedral site, which explains the experimental observation of fall in Curie temperature with Yb substitution.

To download the article click on the link below:

https://arxiv.org/pdf/1704.02454.pdf