Impact of vanadium substitution on structural, magnetic, microwave absorption features and hyperfine interactions of SrCo hexaferrites

The Co-V co-substituted nano Sr-hexaferrite, Sr_0.5Co_0.5V_xFe_12−xO₁₉ (0.00 ≤ x ≤ 0.08) (V→SrCo (0.00 ≤ x ≤ 0.08) NHFs), were manufactured by citrate combustion route. The microstructure, morphology, magnetic features, hyperfine interactions and oxidation state and chemical composition of products explained by XRD, SEM with EDX, HR-TEM, VSM, Mossbauer spectrometry, and XPS, respectively. The D_XRD (Average crystallite size) of products were assessed via Scherrer formula as within the range of 37 and 83 nm. The hexagonal morphology and chemical composition of the products was presented by TEM, HR-TEM, SEM and EDX analyses. The XPS analysis provided both the composition and oxidation states of prepared NHFs. Mossbauer spectra showed that the s electron density around Fe³⁺ ions of all sites except 12k influenced V³⁺ content. The coercivity data indicates that all samples denote a magnetically hard material at both low and high temperatures. M_s, M_r and n_B fluctuate with respect to dopant concentration and attain their highest magnitudes for the V→SrCo (x = 0.04) NHFs. A SQR of around 0.5 is achieved at each temperature, reflecting a relatively high large anisotropy field. The field-cooling (FC) curves of all samples yield a drop in magnetization with increasing temperature. Their irreversibility temperature is detected to be beyond 325 K. Both M-H and M-T imply the ferrimagnetic behavior of different samples. Microwave properties were measured between 2 and 18 GHz as S11-S21 parameters. It demonstrated non-linear behavior of the microwave properties vs. V concentration. The origin of the reflection losses in NHVs can be explained by the dipole polarization processes.