Dilute magnetic semiconductor

Since the first theoretical prediction of room-temperature ferromagnetism in dilute magnetic semiconductors (DMS) (T. Dietl et al., Science 287, 1019-1022 (2000)), much work, both theoretical and experimental, had been devoted to the investigation of ferromagnetism in ZnO doped with various transition metals in early 2000s. Although most theoretical predications as well as majority of experimental studies favoured room-temperature ferromagnetism in transition metal doped ZnO, the origin of the observed ferromagnetic behaviour remained debatable. Some of the factors that have caused the difficulties are (i) different preparation methods always led to different results, (ii) there was no clear correlation between different characterization techniques and each technique focuses on different regions either in real space or in the energy domain and (iii) there was a lack of systematic studies. In order to gain a deep understanding of the magnetic ordering mechanism in ZnO:Co, we had carried out a systematic study of Zn1–xCoxO thin films by varying the Co composition from x = 0 to 0.33. We characterized all samples thoroughly using a variety of techniques. Special effort had been made to ensure that a series of characterization experiments could be performed on each of the series of samples studied. We found that the ferromagnetic signal of ZnO:Co is of intrinsic origin.

[1] Tay M et al., "Ferromagnetism in inhomogeneous Zn1–xCoxO thin films", J. Appl. Phys. 100, 063910 (2006).

[2] T. Dietl et al., “Origin of ferromagnetism in Zn1–xCoxO from magnetization and spin-dependent magnetoresistance measurements”, Phys. Rev. B 76, 155312 (2007).

[3] Tay M et al., “Structural, optical, magnetic and electrical properties of Zn1-xCoxO thin films”, J. Mater. Sci. – Mater. Elect. 20, 60-73 (2009).