Effect of Mo substitution on structure, morphology and magnetic features of Sr0.8Ni0.2Fe12-2xMoxO19 (x ? 0.35) hexaferrites

Abstract

Sr0.8Ni0.2Fe12-2xMoxO19 (x <= 0.35) nanohexaferrites (NHFs) were obtained by a sol-gel combustion route. The phase identification was performed through X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HR-TEM). The morphological and chemical composition analyses were verified by scanning electron microscope (SEM) and energy dispersive X-rays (EDX), respectively. The crystallite size (D-XRD) of all produced samples has been estimated between 31 and 56 nm. Magnetization versus applied magnetic field (M-H) measurements of different products were conducted at 300 K (room temperature, RT) and 10 K, and the results revealed their ferrimagnetic character. Undoped Sr0.8Ni0.2Fe12O19 NHFs have the maximum magnetic parameters at both temperatures. 10 K magnetization data such as M-S (saturation magnetization), M-r (remnant magnetization), n(B) (magneton number), and H-C (coercivity) belonging to Sr0.8Ni0.2Fe12O19 NHFs are M-S,M-max = 99.6 emu/g, M-r,M-max = 48.2 emu/g, n(B,max) = 18.83 mu(B), and H-C,H-max = 3406 Oe, respectively. Moreover, the squareness ratio (SQR = M-r/M-S) is 0.489 at RT and 0.484 at 10 K. Those magnitudes assign the single-domain structure with uniaxial crystal anisotropy for this hexagonal product at both temperatures. Some magnetic parameters like coercivities (in a range of (286-475) Oe) and M-r (in a range of (7.8-14.1) emu/g) drop sharply due to the Mo6+ doping process. Calculated SQR values are between 0.111 and 0.206, which indicate the multi-domain wall structure for NHFs at both temperatures. Undoped Sr0.8Ni0.2Fe12O19 NHFs can be classified as magnetically hard materials, while Mo-doped samples can be classified as soft magnetic materials.