Influence of Co2+–Al3+ Co-doping on the magnetic, dielectric, and electrochemical behavior of M-type Ba-Sr hexaferrites

Herein, we report the effect of Co 2+ -Al 3+ co-substitution (x = 0.0–0.40) on the structural, magnetic, dielectric and electrochemical properties of Ba 0.2 Sr 0.8 Fe 12-2x Co x Al x O 19 (BaSrM) synthesized using sol-gel auto-combustion method (SGACM). XRD data shows that the crystal structure is hexagonal and ‘a’ and ‘c’ parameters show a decreasing trend with an increase in dopant concentration. All samples are phase pure and display c/a ratio between 3.92 and 3.93, which confirms their M-type nature. With the increase in calcination temperature segregation of Fe 2 0 3 and CoFe 2 O 4 is observed in doped samples. The highest magnetic saturation (67.07 emu/g) and magnetic remanence (36.75 emu/g) values were noticed in x = 0.1 sample. The coercivity (H c ) value continuously declined from 6001 to 3501 Oe with an increment in dopant content from x = 0.0–0.4. The highest value of the dielectric constant (≈ 273) was observed for the x = 0.4 sample. Temperature-dependent dielectric studies revealed an increasing trend of dielectric constant with temperature. Cyclic voltammetry shows the highest specific capacitance (9.829 F/g) value for x = 0.4 sample. Tafel analysis confirms reduction in catalytic activity with doping. The greater than 3500 Oe coercivity observed in these samples indicates their potential in a plethora of permanent magnetic applications.