Understanding better effect of heat treatment on magnetic properties of nanocrystalline barium ferrite (BaM)

Aim. the beginning of this paper, we review recent publications^[1-4] and point out that, in order to obtain better and better inherent magnetic properties of BaFe₁₂O₁₉, customarily shortened to BaM, it is necessary to understand better the effect of heat treatment on its magnetic properties. In the full paper, we explain the effects in some detail; in this abstract, we just add some pertinent remarks to listing the two topics of explanation. The first topic is: experimental materials and method. In this topic, we use the X-ray diffractometer, infrared spectrometer, vibrating sample magnetometer and field emission scanning electron microscope to study the composition, magnetic properties and grain size of BaM. The second topic is; results and their discussion. Its four subtopics are: the phase constitution and generation of BaM intermediate products (subtopic 2.1), the effects of calcination temperature on the phase constitution and magnetic properties (subtopic 2.2), the effect of calcination time on the phase constitution and magnetic properties (subtopic 2.3) and the morphology of BaM and the comparison of its magnetic properties with those reported abroad (subtopic 2.4). In subtopic 2.1, we find that the transitional phase of BaM occurs at the temperature of 500°C/4 h and that the primary phase of its intermediate product is 7-Fe₂O₃. Also in subtopic 2.1, we find that the saturated magnetic strength is 52.6 A·m²·kg^-1 and the coercivity is close to zero. In subtopic 2.2, we point out that the single-phase BaM of proper grain size is formed at the temperature of 800°C/4h or 900°C/3h; increasing the temperature and time helps increase both saturated and residual magnetic strengths. In subtopic 2.3, we observe that; when the BaM is calcined for 4 to 6 hours, the magnetic energy properties are the best; when the BaM is calcined for 6 hours and annealed for two hours, its magnetic properties are not affected. In subtopic 2.4, we compare the magnetic properties of the BaM with those reported abroad, the comparison results being summarized in Table 1.