Transition from ferromagnetism to diamagnetism in undoped ZnO thin films

Abstract

We report a systematic study of the film thickness dependence (0.1–1 μm) of room-temperature ferromagnetism in pure magnetron-sputtered ZnO thin films wherein a sequential transition from ferromagnetism to paramagnetism and diamagnetism as a function of film thickness is observed. The highest saturation magnetization (MS) value observed is 0.62 emu/g (0.018 μB/unit cell) for a ∼480 nm film. On doping the ZnO film with 1 at. % Mn enhances the MS value by 26%. The ferromagnetic order in ZnO matrix is believed to be defect induced. In addition, on doping with Mn hybridization between the 2p states of O and the 3d states of Mn occurs.

Enhanced ferromagnetism in single crystalline Co-doped ZnO thin films by Al codoping

“…Theoretically, Dietl et al first predicted that p-type Mn doped ZnO would show ferromagnetism with T C well above RT [3]. In contrast, Co-doped ZnO was theoretically predicated to become ferromagnetic with n-type doping [4] and a flood of experimental studies of this subject have been reported upon [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. However, the presented data were plagued by instability and a lack of reproducibility.…”

“…Additionally, it is surprising that several groups observed distinct ferromagnetic signals in ZnO thin films and nano-particles without TM doping [16,17], and it seems that the charge-transfer ferromagnetism model can give a satisfactory explanation for them [18]. However, in all the above cases, they are not true DMSs.…”

Thin film of ZnAl2O4:Eu3+ synthesized by a non-alkoxide precursor sol-gel method

“…From this value, we can estimate that the size of the particles forming the film is less than 30 nm. Recently, Kapilashrami et al 19 used the same technique (cross-section) to determine the thickness of ZnO films measuring between ca. 150 and 1000 nm.…”

Thin film epitaxy and magnetic properties of STO/TiN buffered ZnO on Si(0 0 1) substrates

“…Recently room temperature ferromagnetism (RTFM) has been widely reported in undoped oxides, such as ZnO [12,13], HfO 2 [14], TiO 2 [15], SnO 2 and In 2 O 3 [16] containing no transition metal doping. This so-called d 0 ferromagnetism has challenged our understanding of the origin of ferromagnetism in these undoped oxides.…”