Effects of bismuth substitution on [Tb.sub.3-x][Bi.sub.x][Fe.sub.5][O.sub.12]

X-ray diffraction, vibrating sample magnetometer and Mossbauer spectroscopy are used for studying the crystallographic and magnetic properties of [Tb.sub.3-x][Bi.sub.x][Fe.sub.5][O.sub.12] (x = 0.5, 0.75, 1.0 and 1.25). The saturation magnetization at room temperature has increased linearly with increase of bismuth concentration, which is due to the strong exchange interaction between a and d sublattices with increase of bismuth concentration.