⁵⁷Fe Mössbauer spectroscopic study on the magnetic properties of tantalum-doped maghemite and hematite

Unique and distinct structural and magnetic characteristics of Fe₂O₃ have been continuously studied for their broad potential and applications, and various attempts were conducted to enhance the properties. Ta⁵⁺-doped Fe₂O₃ were synthesized using sol-gel method followed by calcination at various temperatures. The formation mechanism based on PXRD and TEM EDS shows that Ta was included in Fe₂O₃ structure during γ phase then shifted to the surface during transformation to α phase, resulting in big hematite particle with small particle of FeTaO₄ on the surface. Ta doping shows an influence on γ-Fe₂O₃ by increasing its stability and a significant influence on the magnetic properties of hematite. 1.9%Ta-doped samples calcined at 500 and 700 ºC show the coexistence of antiferromagnetism and weak ferromagnetism at 78 K. For the α-Fe₂O₃ including 7.4 atomic percent of Ta calcined at 700 ºC, the particle shows large size of 300 nm but there is no Morin transition temperature (T_M) at 78 K.