Possible metamagnetic origin of ferromagnetism in transition-metal-doped SnO ₂

Room-temperature ferromagnetism has been observed recently in Co and Fe doped SnO2 powders. In Sn0.99 Co0.01 O2 powders prepared at 600 °C, ferromagnetism emerged following a sharp transition in the M vs H data at a critical field ~25 kOe. Broad susceptibility maxima were observed in ferromagnetic Sn1-x Cox O2 and Sn1-x Fex O2 powders centered near 290 and 260 K, respectively, indicating spin fluctuation effects. High temperature magnetic measurements of Sn0.99 Co0.01 O2 and Sn0.99 Fe0.01 O2 obtained TC 's of 440 and 850 K respectively. However, unlike conventional ferromagnets, the magnetic transitions at the TC were associated with sharp changes in M. It is argued that these observed unusual magnetic features indicate a metamagnetic origin of the room-temperature ferromagnetism in Co and Fe doped SnO2.