Novel magnetic materials for spin electronic applications

Abstract

Among various types of semiconductors, oxide semiconductors are the most promising host compounds to realise high Curie temperatures with transition metal doping. Room temperature ferromagnetism in dilute oxide semiconductors was first reported in anatase and rutile phases of Ti02 doped with Co in 2001. Various other transition metal doped oxide semiconductors (SnO2, ZnO) have been reported to be ferromagnetic at room temperature. High temperature ferromagnetism is not expected in these materials because the magnetic doping level is far below the cation percolation threshold Xp needed for long-range order based on superexchange or double exchange interactions. These reports were greeted with scepticism, and the belief that the data somehow reflected the presence of secondary ferromagnetic phases rather than intrinsic long range ferromagnetism. The possibility of an extrinsic origin for the ferromagnetism, such as ferromagnetic impurity segregation, could not be ruled out in some cases. To understand better the origin of the magnetism in these novel magnetic systems we have carried out careful systematic analysis of three systems; -- 1. Sn1-xMxO2, where M = Mn, Fe or Co, 0 ≤ x ≤ 0.3 -- 2. Zn1-xMxO for M = Sc - Cu where x = 0.05 nominally, and Zn1_xCoxO where 0 ≤ x ≤ 0.25 -- 3. Hf1-xCox02 where 0 ≤ x ≤ 0.03, and Hf1-xMxO2 where M = Sc, Ti and Ta and x = 0.05 nominally