Magnetic properties of iron-boron-oxide and iron-phosphor-oxide glasses prepared by sol-gel method

The magnetic properties of powders made from dried gel were measured as a function of calcination temperature up to 600°C. The magnetic moment of iron oxide was enhanced by adding a small amount of boron. A maximum moment of 49.5 emu/g, which is about a 20% increase over that of nondoped Fe-O powders, was obtained at the mol. ratio of B/(Fe+B)=0.2. Doping with phosphorus, on the contrary, diminishes the magnetic moment. In both cases, the magnetic moment is considered to originate from fine maghemite particles dispersed in a glass network. The addition of such glass-forming elements as boron and phosphorus suppresses the growth of iron-oxide particles as well as the crystallographic transition from maghemite to hematite at elevated calcination temperature. The suppression is more pronounced for phosphorus than for boron. In addition, Fe B-O thin films were prepared by spin-coating an Fe-B-O gel solution on glass substrates. A large magnetization exceeding 3 kG was obtained after the gel was dried at 200°C in air and subsequently annealed at 400°C in a vacuum. It is found that a key factor in the realization of films with large magnetization is to dry the coated gel at low temperature. X-ray diffraction of the films shows a hollow pattern, indicating that they consist of very fine maghemite particles