Structure and magnetic properties of K2NiFe3.5V3.5O16 with the hollandite structure

Abstract K2NiFe3.5V3.5O16 with the hollandite structure was prepared by conventional ceramic method. The specimen exhibited the ferrimagnetic behaviour with a relatively high Curie temperature of approximately 870 K and a room temperature saturation magnetization of ∼15 emu/g. A maximum of magnetization appeared at 120–150 K and a relatively abrupt decrease in magnetization was detected below 100 K, accompanied by a change of slope in temperature-dependent resistance. The Mossbauer spectra could be well fitted with two sextets in the temperature range of 78–290 K. A change in average hyperfine field and chemical shift was observed below 150 K.