Magnetic property enhancement of cobalt-free M-type strontium hexagonal ferrites by CaCO3 and SiO2 addition

An experiment was performed to investigate whether CaCO3 and SiO2 addition enhances the magnetic properties of cobalt-free M-type Sr ferrites, in which experimental parameters such as additive composition and the CaCO3/SiO2 ratio were changed. The specimens were prepared using conventional ceramic techniques. CaCO3 addition promoted densification and uniform grain growth, resulting in high remanence; however, with the simultaneous addition of CaCO3 and SiO2, coercivity decreased to 3046 Oe in Sr ferrite hard magnets without Co3O4. SiO2 addition suppressed grain growth. The addition of appropriate concentrations of CaCO3 and SiO2 as additives after calcination was shown to be very beneficial for tailoring a dense microstructure with relatively small grains. A CaCO3/SiO2 ratio of approximately 1.8 was found to be optimum, and the magnetic properties of Br = 4.3 kG, iHc = 3.7 kOe, and (BH)max = 4.5 MGOe were obtained for Sr ferrite hard magnets without Co3O4, which are acceptable for motor applications under output power <1 kW.