Virginie Brizé

Observation of ferromagnetism at room temperature in ZnO thin films

Room-temperature ferromagnetism (FM) has been observed in laser-ablated ZnO thin films. The FM in this type of compound does not stem from oxygen vacancies as in the case of TiO2 and HfO2 films, but from defects on Zn sites. Magnetization of very thin films is much larger than that of the thicker films, showing that defects must be located mostly at the surface and/or the interface between the film and the substrate. Results on Fe-doped ZnO and Mn-doped ZnO films reveal clearly that the metal-transition doping does not play any essential role in introducing the magnetism in ZnO.

Room temperature ferromagnetism in laser ablated Ni-doped In2O3 thin films

Ni-doped In2O3 thin films were fabricated by laser ablation on sapphire and MgO substrates under various conditions. All Ni:In2O3 films are well-crystallized, single phase, and show clear evidences of room temperature ferromagnetism (FM). Ni atoms were well substituted for In atoms, and distributed very uniformly over the whole thickness of the films. However, the films grown at 550 °C have the Ni concentration exactly the same as in the synthesized target, and as the results, they have the best crystallinity and the largest magnetic moment (maximum about 0.7μB∕Ni). The observed FM in this type of wide-band gap semiconductors has proved that by applying appropriate growth conditions, doping few percent of Ni into In2O3 could indeed result in a potential magnetic material.

Mn-doped ZnO and (Mn, Cu)-doped ZnO thin films: Does the Cu doping indeed play a key role in tuning the ferromagnetism?

Zn0.9Mn0.1O and Zn0.85Mn0.1Cu0.05O thin films were grown by the pulsed laser deposition technique on R-cut Al2O3 substrates under various conditions. Both Zn0.9Mn0.1O and Zn0.85Mn0.1Cu0.05O films that were fabricated at 650 °C under an oxygen pressure of 0.1 Torr show ferromagnetism (FM) above room temperature. It appears that by applying appropriate conditions, doping Mn alone can induce FM in ZnO itself, while co-doping with Cu might enhance the magnetic moment for some extent in some specific cases, but not very crucially as theories have predicted. Growth conditions likely play more important roles to result in ferromagnetic samples.

Magnetism in transition-metal-doped In2O3 thin films

Laser ablated transition-metal (TM)-doped In2O3 thin films grown under appropriate conditions on both MgO and Al2O3 substrates can be well crystallized and ferromagnetic at room temperature. Of all the dopants, Ni seems to be the most promising candidate since doping Ni in In2O3 results in semiconducting films with the largest magnetic moment. Films are cluster-free. Magnetic force microscopy measurements confirm that the magnetic signals at room temperature are real. Moreover, compared to TM:In2O3 films deposited on MgO, films on Al2O3 have smaller grains and those are better connected, so that the film texture is smoother and the magnetic domains are more uniform. The size of ferromagnetic domains is determined to be about 1 µm. The room temperature ferromagnetism in V/Cr/Fe/Co/Ni-doped In2O3 films probably originates from the doped In2O3 matrices.

Does Mn doping play any key role in tailoring the ferromagnetic ordering of TiO2 thin films

Mn was doped into TiO2 to clarify the real effects of Mn doping on magnetic and structural properties of TiO2 thin films. Mn doping does not play any key role in introducing ferromagnetism (FM) in the system. When the dopant concentration is small (below 5%), the Mn atoms can still be substituted for Ti atoms and maintain the TiO2 structure, so that it enhances the magnetic moment of the TiO2 host to some extent. When the dopant content increases to larger than 10%, along with a destruction of the anatase structure, the Mn doping consequently degrades and then destroys the FM of the host.

Undoped TiO2 and nitrogen-doped TiO2 thin films deposited by atomic layer deposition on planar and architectured surfaces for photovoltaic applications

Undoped and nitrogen doped TiO2 thin films were deposited by atomic layer deposition on planar substrates. Deposition on 3D-architecture substrates made of metallic foams was also investigated to propose architectured photovoltaic stack fabrication. All the films were deposited at 265 degrees C and nitrogen incorporation was achieved by using titanium isopropoxide, NH3 and/or N2O as precursors. The maximum nitrogen incorporation level obtained in this study was 2.9 at. %, resulting in films exhibiting a resistivity of 115 Omega cm (+/-10 Omega cm) combined with an average total transmittance of 60% in the 400-1000 nm wavelength range. Eventually, TiO2 thin films were deposited on the 3D metallic foam template.

Ferromagnetic transition-metal-doped tin dioxide thin films

Induced ferromagnetism (FM) above room temperature in Cr/Ni/V-doped SnO/sub 2/ thin films was studied. 200 nm-thick films were grown using pulsed laser deposition technique. Structural study, magnetization measurements and chemical composition determination were done through X-ray diffraction, magnetic force microscopy at room temperature and Rutherford backscattering spectroscopy. Findings prove that doping a small amount of transition metal in nonmagnetic oxides could introduce FM thru Ruderman, Kittel, Kasuya, and Yoshida (RKKY) interaction.