Pengaruh proses perlakuan panas terhadap ukuran kristal dan sifat magnetik BaFe12O19 didoping bi dibuat melalui metode sol gel = The influence of heat treatment on the crystallite size and magnetic properties of BaFe12O19 doped by bi made by sol gels method (Fakultas Matematika dan Ilmu Pengetahuan Alam Universitas Indonesia, 2012)