Crystal strain, chemical bonding, magnetic and magnetostrictive properties of erbium (Er3+) ion substituted cobalt-rich ferrite (Co1.1Fe1.9−xErxO4)

Abstract

Erbium (Er) substituted nanocrystalline cobalt-rich Co_1.1Fe_1.9−xEr_xO₄ (x = 0.00–0.20) has been synthesized by the sol gel auto-combustion method. The crystal structure with induced strain, chemical bonding, magnetic and magnetostrictive properties of Co_1.1Fe_1.9−xEr_xO₄ have been studied as a function of the Er content. X-ray diffraction results confirmed the pure phase formation of the spinel cubic lattice for erbium (Er) substitution up to x ≤ 0.10; for x ≥ 0.15, a small amount of secondary orthoferrite phase ErFeO₃ begins to form, in addition to the required Co_1.1Fe_1.9−xEr_xO₄. Erbium substitution for Fe in Co_1.1Fe_1.9O₄ introduces strain due to its larger ionic radius which is also supported by the red shift observed in Raman spectra. All the samples show typical magnetic hysteresis behavior with a decrease in magnetization due to the weak superexchange interaction and an increase in coercivity as a function of Er content. The maximum values of the magnetostriction coefficient (λ₁₁ = −210 ppm at 2.2 kOe) and strain derivative (dλ/dH = 327 × 10³ ppm Oe⁻¹) are obtained for Er, x = 0.05. The decrease in Curie temperature from 455 °C to 378 °C, with Er content, indicates the decrease in strength of the overall A–B superexchange coupling of Co_1.1Fe_1.9−xEr_xO₄. The magnetic and magnetostrictive properties authenticate the significance of the prepared samples for memory storage and stress sensing applications.