Effect of La3+and Al3+ doping on the crystal structure and magnetic properties of strontium hexaferrites

Abstract

Modification of crystal structure and magnetic properties of M-type strontium hexaferrites (SrM) doped with foreign ions (Al3+, La3+) was studied, focusing on the distortion of the lattice. Incorporation of Al3+ ions contracted the lattice of SrM and hardened lattice vibration modes with lattice disorders. X-ray diffraction examined the lattice distortion of FeO5 trigonal bipyramidal sites (TBP) revealing that off-center displacement (z0) was reduced to z0 = 0 by heavy Al3+ doping. This reduction of z0 was attributed to stabilization of single-well potential in the positioning of Fe3+ ions in TBP. Furthermore, La3+ doping led to a more significant contraction of the lattice and restored a non-zero off-center displacement of Fe3+ ion in TBP. The polycrystalline ceramics with high coercivity exceeding 21 kOe through the conventional ceramic processing route with concomitant La3+ and Al3+ doping.