Induced Room-Temperature Ferromagnetism in Un-doped Nanocrystalline Metal Oxide Powders Obtained by Mechanical Milling: A Review

In the past few years, considerable research work has been carried out in order to understand the origin of ferromagnetism in un-doped oxide semiconductors. The debate is still open, but most of the experimental and theoretical studies suggested that defects may induce room-temperature ferromagnetic order. This brief review will focus on some very recent works based on the use of mechanical milling as a processing approach in order to induce defects and transform the initial diamagnetic or paramagnetic powders to ferromagnetic order.