Antoine Ruyter

Magnetism in Ni-doped SnO2 thin films

Transparent Ni-doped SnO2 thin films grown by the pulsed laser deposition technique on LaAlO3, SrTiO3 as well as R-cut Al2O3 substrates all show room-temperature ferromagnetism (FM). While the Ni-doped SnO2 films on LaAlO3 substrates have a large magnetic moment of about 2 µB/Ni, films grown under the same conditions on SrTiO3 and Al2O3 substrates have a magnetic moment of one order smaller. Magnetic force microscopy measurements confirmed that the Ni:SnO2 films on LaAlO3 are magnetically homogeneous at nanometre-scales, and the FM in the films comes from the doped matrix.

Substrate effects on the room-temperature ferromagnetism in Co-doped TiO2 thin films grown by pulsed laser deposition

Co:TiO2 films were fabricated by laser ablation on Si, LaAlO3 (LAO), and SrTiO3 (STO) substrates from a ceramic target. Films on all types of substrates have Curie temperature (TC) above 400 K. All films are highly crystallized with different structures. While films on Si substrates are rutile, films on LAO and STO substrates are single phased anatase. Due to the different lattice mismatch, films grown under the same growth conditions on Si, LAO, and STO substrates have different saturation magnetization and coercivity. While Co atoms are mostly localized near the surface of the films, magnetic measurements suggested that the ferromagnetism unlikely originates from Co clusters.

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.

Room temperature ferromagnetism in anatase Ti0.95Cr0.05O2 thin films: clusters or not?

Laser ablated Cr-doped TiO2 thin films grown on LaAlO3 substrates are single phased anatase and room temperature ferromagnetic. The magnetic moment of Cr-doped TiO2 films is rather large, and it is consistent with the theoretical predictions. Magnetic force microscopy measurements certainly suggested that the strong ferromagnetism at high temperature in Cr-doped TiO2 films is intrinsic, and it must originate from the diluted magnetic matrix but not from any form of clusters.

Laser ablated Ni-doped HfO2 thin films: Room temperature ferromagnets

Laser ablated Ni-doped HfO2 thin films fabricated under a wide range of growth conditions all showed ferromagnetism above room temperature. However, the films deposited at 800°C under an oxygen partial pressure of 10−6Torr have the largest magnetic moment of 2.7μB∕Ni. Ni-doped HfO2 films also well demonstrate a large anisotropy. Magnetic force microscopy measurements confirmed that Ni-doped HfO2 films are real room temperature ferromagnets with a domain structure, and that the size of magnetic domains is larger than 10μm.

Magnetic structure of V:TiO2 and Cr:TiO2 thin films from magnetic force microscopy measurements

Ferromagnetic V-doped TiO2 and Cr-doped TiO2 films were fabricated by the pulsed laser deposition technique on LaAlO3 substrates. All V∕Cr:TiO2 films are single phased anatase, well epitaxial, c-axis oriented, and strongly ferromagnetic at room temperature. Besides giving evidences for a great flatness and magnetic homogeneities of those films, magnetic force microscopy measurements implied that the V∕Cr-doped TiO2 films seem to have a diluted magnetic structure with the ferrmagnetism originated from the doped matrix rather than any type of magnetic clusters. The size of the ferromagnetic domains was assumed to be 5–10 μm.

Room temperature ferromagnetism in laser ablated transition-metal-doped TiO2 thin films on various types of substrates

Under appropriate growth conditions, transition-metal-doped TiO2 (V/Cr/Fe/Co/Ni : TiO2) thin films deposited on various types of substrates by laser ablation could be ferromagnetic above room temperature. As for LaAlO3 substrates, which seem to be the best, when the growth temperature was 650°C, Fe/Co/Ni-doped TiO2 films could achieve a magnetic moment one order larger than that of films grown at 700°C, in the range of 1.5–2.9µB per impurity atom. These values are the largest for iron-group-doped-TiO2 that have been obtained so far. More interestingly, V/Cr-doped TiO2 films grown at both 650°C and 700°C could also have a large magnetic moment; however, growing at 650°C gives rise to a much larger one. Among all the transition-doped TiO2 thin films, the largest magnetic moment obtained is 4.3µB/V for V : TiO2 films grown at 650°C. Besides the convincing data from x-ray diffraction and magnetization, magnetic force microscopy measurements strongly suggest that the room temperature ferromagnetism in our films does not stem from any kind of dopant clusters. These genuine room temperature ferromagnets with very large magnetic moments appear to be very promising for applications.

Correlation between structural defects and properties in large La–Sr–Mn–O single crystals

Structural, magnetic, and electrical properties of La0.8Sr0.2MnO3 single crystals grown by the floating zone technique have been investigated using x-ray Laue diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy and magnetic force microscopy (MFM) magnetization and resistivity measurements. The aim of this work was to identify growth defects and their possible correlation with the transport properties or magnetic self-organization. The analysis by x-ray Laue diffraction and SEM reveals large single crystal structure without any extended microdefects and with a homogeneous composition. TEM observations show nanometric defects present only in the central part of the grown rod and allow to identify these defects as nanocracks resulting from a high stress gradient during the growth. Transport measurements indicate that there is an effect of the variation of oxygen content but the conducting behavior between 300 and 5K is not affected by the prese...

Correlation between crystallinity and magnetism in a series of laser-ablated anatase Ti1−xCoxO2 thin films

We report on ferromagnetic Co-doped TiO2 films grown by laser ablation on LaAlO3 and SrTiO3 substrates. Films on both types of substrate are highly crystallized, very well epitaxial, single-phased anatase and show ferromagnetism far beyond room temperature. Due to the smaller lattice mismatch in the case of LaAlO3 substrates, films on LaAlO3 substrates are more oriented than films on SrTiO3 substrates, and therefore have better quality with a larger saturation magnetic moment. Besides x-ray diffraction data, our magnetic force microscopy results also suggest that the ferromagnetism in Co-doped TiO2 films probably does not stem from either Co-enriched TiO2 clusters or Co segregations.