Magnetic and dipole moments in indium doped barium hexaferrites

Highlights: • Structure vs. temperature for BaFe_12−xIn_xO₁₉ x = 0.1, 1.2 was investigated. • Atomic coordinates and lattice parameters were Rietveld refined. • Exchange interactions vs. structure were investigated. • Magnetic and dipole moments at different position per iron ion were defined. • Spontaneous polarization for these compositions was established at 300 K. Crystal and magnetic structure of the doped BaFe_12−xIn_xO₁₉ samples were refined by the results of investigations using high resolution neutron powder diffraction and vibration sample magnetometry at different temperatures. The refinements were realized in frame of two space groups. The P6₃/mmc (No 194) centrosymmetric nonpolar and P6₃mc (No 186) noncentrosymmetric polar space groups were used. The unit cell parameters, ionic coordinates, thermal isotropic factors, occupation positions, bond lengths and bond angles, microstrain values were established. The magnetic and dipole moments were also defined. It is established that the In³⁺ cations may be located only in the Fe1 – 2a and Fe2 – 2b crystallographic positions with equal probability for the sample with lowest substitution level x = 0.1. At the x = 1.2 substitution level about half of the In³⁺ cations occupies the Fe5 – 12 k positions. For the last sample the remaining half of the In³⁺ cations is equiprobably located in the Fe1 – 2a and Fe2 – 2b positions. The spontaneous polarization was established for these compositions at 300 K. It is studied the influence of the type of substitutive cation and structural parameters on the Fe³⁺(i) – O²⁻ – Fe³⁺(j) (i, j = 1, 2, 3, 4, 5) indirect superexchange interactions with temperature. With substitution level increase the superexchange interactions between the magnetic positions inside and outside the sublattices are broken which leads to a decrease in the value of their magnetic moments.