Magnetic, magnetodielectric, and magnetoimpedance correlations in co-substituted (Co, Ho) KBiFe2O5 at room temperature

Abstract

The exotic physical properties of unique brownmillerite KBiFe2O5 (HC0) are enhanced by co-substituting rare-earth Holmium (Ho) and transition metal Cobalt (Co), ion and establishing their interaction. Dielectric, structural, magnetic, magnetodielectric (MD), and magnetoimpedance (MI) properties of co-substituted KBi1−xHoxFe2(1−y)CoyO5 [x = y = 0, 0.05, 0.1, & 0.15] are investigated. The solid-state reaction method is used to synthesize, and the Rietveld refined powder X-ray diffraction patterns confirm the monoclinic structure with the P2/c space group. The Raman shift decreases, but the lattice strain increases with increased co-doping and correlates with MD data. The room temperature (RT) remnant (MR) and saturation (MS) magnetization increase by ∼ 20 and ∼ 2 times, respectively, with co-doping. The magnetic anomaly near dielectric transition (∼ 500 °C for KBi0.95Ho0.05Fe1.9Co0.05O5) suggests the signature of MD coupling for the co-doped samples. The MD and magneto-loss (ML) strength of HC0 increase with co-doping from 0.35 % to 0.65 % and 0.65 % to 1.25 %, respectively. In addition, the MD coupling coefficient increases from 4 % to 11 %, with the increase in co-doping. The RT MI curve of KBi0.85Ho0.15Fe1.75Co0.15O5 (HC15) shows an enhanced symmetric hysteresis loop (butterfly-like) with a maximum strength of ∼ 0.6 %. The frequency-dependent MD of HC0 shows that the maximum MD% at a high frequency (> 50 kHz) is enhanced with the increase in co-doping, and the corresponding MD and ML strength of HC15 are − 1.2 % and − 0.4 %, respectively. The dielectric relaxation time for HC15 shows maximum non-linear variation with the magnetic field, suggesting an intrinsic contribution to MD coupling. The observed dielectric transition (TC) around 510 °C of HC0 decreases to 480 °C (for HC15) with the increase in the co-doping. Thus, enhanced MD coupling and magnetic field-controlled dielectric relaxation for co-doped HC0 make this material suitable for next-generation spintronic and storage device applications.