**Abstract**

Due to their potential application in the field of spintronics, the discovery of various types of oxide-based dilute magnetic semiconductors (ODMS) materials that might work at practical room temperature ferromagnetism (RTFM) has recently attracted great attention. Among ODMS materials, transition metal™ doped tin oxide (SnO2) compounds are important for the investigation of ferromagnetism due to its special important property such as high chemical stability, high carrier density, n-type behavior and trait long range ferromagnetism. However, the question of understanding the mechanism of ferromagnetism (FM) process is still not fully understood in these materials, due to unable to know exactly whether its FM property arises from the nature of the intrinsic property or secondary phases of the material. According to the results from many literature surveys, the mechanism of magnetic ordering responsible for magnetic exchange interaction in these materials is highly affected by oxygen vacancy, defects, dopant types and concentration, temperature, sample preparation method and so on. In this chapter, we reviewed the mechanism of ferromagnetism observed of Ni, Mn and Fe-doped SnO2 materials.

**Keywords:** spintronics, diluted magnetic semiconductors (DMS), room temperature ferromagnetism (RTFM), TM doped tin oxide, oxygen vacancy and defect
