W. Prellier

Oxide-diluted magnetic semiconductors: a review of the experimental status

Oxide-diluted magnetic semiconductors (O-DMS) have attracted a great deal of interest in recent years due to the possibility of inducing room temperature ferromagnetism. These materials are of particular interest for spintronic devices such as spin valves. This review describes the experimental status of the O-DMS including the recent results on ZnO- and TiO2-based systems.

Colossal-magnetoresistive manganite thin films

Mixed-valence perovskite manganites (Re1-xAxMnO3 where Re = rare earth, A = alkaline earth) provide a unique opportunity to study the relationships between the structure and the magnetotransport properties due to an interplay among charge carriers, magnetic coupling, orbital ordering and structural distortion. This makes these compounds very exciting from both the basic research and from the technological viewpoint. As the technology pursued with these materials requires film growth, extensive studies have been made on materials synthesis, structural and physical characterization and device fabrication. In this article, the results from the different experimental techniques and the effects of the deposition procedure of the manganite thin films are first reviewed. Second, the relation between the structural and the physical properties is mentioned, and the influence of strains discussed. Finally, possible applications of manganite thin films in spin electronics are presented.

Laser ablation of Co:ZnO films deposited from Zn and Co metal targets on (0001) Al2O3 substrates

We report on the synthesis of high-quality Co-doped ZnO thin films using the pulsed laser deposition technique on (0001)-Al2O3 substrates performed in an oxidizing atmosphere, using Zn and Co metallic targets. We first optimized the growth of ZnO in order to obtain the less strained film. Highly crystallized Co:ZnO thin films are obtained by an alternative deposition from Zn and Co metal targets. This procedure allows an homogenous repartition of the Co in the ZnO wurzite structure which is confirmed by the linear dependence of the out-of-plane lattice parameter as a function of the Co dopant. In the case of 5% Co doped, the film exhibits ferromagnetism with a Curie temperature close to the room temperature.

Transparent Cr-doped SnO2 thin films: ferromagnetism beyond room temperature with a giant magnetic moment

Laser ablated Cr-doped SnO2 thin films grown on various kinds of substrates all show ferromagnetism well beyond room temperature. Surprisingly, films of Sn0.95Cr0.05O2 grown on LaAlO3 substrates have a giant magnetic moment of 6 μB/Cr, which is 20–30 times larger than that of films grown under the same conditions on SrTiO3 and R-cut sapphire substrates. All films are highly transparent.

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.

Spectacular decrease of the melting magnetic field in the charge-ordered state of Pr0.5Ca0.5MnO3 films under tensile strain

An insulator to metal transition below 240K is induced by applying a 7T magnetic field in Pr0.5Ca0.5MnO3 thin films grown by the Pulsed Laser Deposition technique on (100) SrTiO3 substrates. This value of the melting magnetic field, much lower that the one required in bulk (20T), is assumed to be an effect of the tensile stress. These results confirm the importance of the bandwidth in the control of the physical properties of this compound and open the route to get colossal magnetoresistive properties by using strain effects.

The Almeida–Thouless line in BiFeO3: is bismuth ferrite a mean field spin glass?

Low-temperature magnetic properties of epitaxial BiFeO(3) (BFO) thin films grown on (111) SrTiO(3) substrates have been studied. Zero-field-cooled and field-cooled magnetization curves show a large discrepancy beginning at a characteristic temperature T(f) that is dependent on the magnetic field strength. T(f)(H) varies according to the well known de Almeida-Thouless line [Formula: see text] suggesting an acentric long-range spin-glass behavior and mean field system.

Magnetocapacitance effect in perovskite-superlattice based multiferroics

We report the structural and magnetoelectrical properties of La0.7Ca0.3MnO3∕BaTiO3 perovskite superlattices grown on (001)-oriented SrTiO3 by the pulsed laser deposition technique. Magnetic hysteresis loops, together with temperature dependent magnetic properties, exhibit well-defined coercivity and magnetic transition temperature (TC) ∼140K. dc electrical studies of films show that the magnetoresistance (MR) is dependent on the BaTiO3 thickness, and negative MR as high as 30% at 100K are observed. The ac electrical studies reveal that the impedance and capacitance in these films vary with the applied magnetic field due to the magnetoelectrical coupling in these structures—a key feature of multiferroics. A negative magnetocapacitance value in the film as high as 3%pertesla at 1kHz and 100K is demonstrated, opening the route for designing novel functional materials.

Spectacular decrease of the melting magnetic field in the charge-ordered state of tensile Pr0.5Ca0.5MnO3 films

An insulator to metal transition below 240K is induced by applying a 7T magnetic field in Pr0.5Ca0.5MnO3 thin films grown by the Pulsed Laser Deposition technique on (100) SrTiO3 substrates. This value of the melting magnetic field, much lower that the one required in bulk (20T), is assumed to be an effect of the tensile stress. These results confirm the importance of the bandwidth in the control of the physical properties of this compound and open the route to get colossal magnetoresistive properties by using strain effects.

Substrate effect on the magnetic microstructure of La0.7Sr0.3MnO3 thin films studied by magnetic force microscopy

Colossal magnetoresistive La0.7Sr0.3MnO3 thin films have been grown under tensile strains on (100)-SrTiO3 substrates and compressive strains on (100)-LaAlO3 and (110)-NdGaO3 substrates by pulsed laser deposition. Using magnetic force microscopy (MFM), a “feather-like” magnetic pattern, characteristic of films with an in-plane magnetization, is observed for films deposited on both SrTiO3 and NdGaO3 while a “bubble” magnetic pattern, typical of films with an out-of-plane magnetization, is recorded for LaAlO3. We show that the shape of the magnetic pattern imaged by MFM is fully correlated to the easy direction of the magnetization in the film.