A systematic study of the growth process of LaMnO 3 (LMO) thin films, by pulsed laser deposition, on top of SrTiO 3 substrates under different oxygen partial pressures (PO 2) is reported. It is found that the accommodation of the orthorhombic LMO phase onto the cubic STO structure, i.e. the amount of structural strain, is controlled by background oxygen pressure. We demonstrate that magnetic behaviour can be continuously tuned from robust ferromagnetic (FM) ordering to an antiferromagnet. These results strongly point to a strain-induced selective orbital occupancy as the origin of the observed FM behaviour, in agreement with recent theoretical calculations.

We report on the magnetic and structural properties of ferromagnetic-insulating La 2 CoMnO 6 thin films grown on top of (001) STO substrates by means of RF sputtering technique. Careful structural analysis, by using synchrotron X-ray diffraction, allows identifying two different crystallographic orientations that are closely related to oxygen stoichiometry and to the features (coercive fields and remanence) of the hysteresis loops.Both Curie temperature and magnetic hysteresis turn out to be dependent on the oxygen stoichiometry. In situ annealing conditions allow tailoring the oxygen content of the films, therefore controlling their microstructure and magnetic properties. PACS: 75.70.Ak, 81.15.Cd 4 Bulk La 2 CoMnO 6 (LCMO) double perovskite has been the subject of strong interest during the last years [ 1,2,3,4,5,6,7] due to its ferromagnetic insulating character.Besides its perspectives as magnetodielectric material, LCMO is a good candidate for active insulating barriers in spin filters. For these devices, insulating barriers must be thin enough to enable tunneling conduction. The properties of epitaxial LCMO thin films have been the subject of some theoretical and experimental works in the recent years [ 8,9,10,11]. Previous experimental reports based on films prepared by pulsed laser deposition (PLD) suggest that magnetic properties are strongly dependent on growth conditions. When samples are grown under low oxygen pressure the Curie temperature (T C ) is around 100K while increasing oxygen pressure (200 mTorr and above) T C values around 230 K can be achieved. Nevertheless, there is no clear consensus on whether this variation of T C comes from differences on the Co/Mn cationic ordering [ 10] or from changes in the oxygen stoichiometry [ 9]. On the other hand, low temperature hysteresis loops reported in the literature present anomalies and "biloop" features that have been attributed to the existence of a bidomain structure in the films. However, these "biloop" features of hysteresis cycles are present up to T C =230K and therefore, cannot be linked to the persistence of regions with low T C phase [ 10].Previous studies report low temperature hysteresis loops with a saturation magnetization close to 6  B /f.u. [ 8,9,10] [ 12,13,14] are antiferromagnetic (AF). Therefore, it is expected that the existence of antisites will reduce the saturation magnetization from 6  B /f.u.. Thus, the departure of the saturation magnetization of a given sample from this saturation value can be interpreted as a measure of the degree of Co/Mn disorder in the structure.The effect of Co/Mn disorder on the magnetic properties has been previously studied in bulk samples (where it can be precisely quantified by means of neutron powder diffraction) [ 6]. These studies show that hysteresis loops become wider (with higher coercive field and lower remanence) in the presence of disorder [ 2,4,6]. Co/Mn ordering temperature is around 1125ºC and the ordering process is blocked below 1000ºC due to extremely large relaxation...

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Modulation of carrier concentration in strongly correlated oxides offers the unique opportunity to induce different phases in the same material, which dramatically change their physical properties, providing novel concepts in oxide electronic devices with engineered functionalities. This work reports on the electric manipulation of the superconducting to insulator phase transition in YBaCuO thin films by electrochemical oxygen doping. Both normal state resistance and the superconducting critical temperature can be reversibly manipulated in confined active volumes of the film by gate-tunable oxygen diffusion. Vertical and lateral oxygen mobility may be finely modulated, at the micro- and nano-scale, by tuning the applied bias voltage and operating temperature thus providing the basis for the design of homogeneous and flexible transistor-like devices with loss-less superconducting drain-source channels. We analyze the experimental results in light of a theoretical model, which incorporates thermally activated and electrically driven volume oxygen diffusion.

Ferromagnetic insulating La 2 CoMnO 6- (LCMO) epitaxial thin films grown on top of SrTiO 3 (001) substrates present a strong magnetic anisotropy favoring the out of plane orientation of the magnetization with a large anisotropy field (70 kOe for film thickness of about 15 nm). Diminishing oxygen off-stoichiometry of the film enhances the anisotropy. We attribute this to the concomitant shrinkage of the out of plane cell parameter and to the increasing of the tensile strain of the films. Consistently, LCMO films grown on (LaAlO 3 ) 0.3 (Sr 2 AlTaO 6 ) 0.7 and LaAlO 3 substrates (with a larger out-ofplane lattice parameter and compressive stress) display in-plane magnetic anisotropy. Thus, we link the strong magnetic anisotropy observed in LCMO to the film stress: tensile strain favors perpendicular anisotropy and compressive stress favors in plane anisotropy. We also report on the thickness dependence of the magnetic properties. Perpendicular anisotropy, saturation magnetization and Curie temperature are maintained over a large range of film thickness. PACS: 75.30.Gw,75.50.Dd, 75.47.Lx, 75.70.Ak I IntroductionSpintronic devices rely on the use of the spin degree of freedom of the electrons as control variable and are presently based on the generation and control of highly spinpolarized currents in ferromagnetic metals [1] or, more recently, on controlling pure spin currents [2]. In this context, ferromagnetic insulators may play an important role as spin sources or spin conductors [3]. In addition, they also have emerged as potential candidates for magnetically active barriers or spin filters [1]. Ferromagnetic insulating materials are scarce since in many cases ferromagnetic interactions are of exchangetype and driven by carriers. Among these rare materials, La 2 CoMnO 6 and La 2 NiMnO 6 double perovskites have been reported to be ferromagnetic insulators when cationic ordering (Co,Ni/Mn) is achieved [4,5]. Ferromagnetic ordering in these materials relies on the Goodenough-Kanamori-Anderson rules that predict a ferromagnetic interaction between Co 2+ or Ni 2+ (t 2g 5 e g 2 and t 2g 6 e g 2 respectively) and Mn 4+ (t 2g 3 ) cations when they are ordered in a fully alternating way in the lattice [6,7,8]. In addition, they have been intensively investigated recently because of claims of magnetodielectric response 2 [9,10], which could be highly interesting for the implementation of new devices including tunable filters, magnetic sensors, and spin-charge transducers [11].Much interest is added when the magnetization of these materials is found to be out-ofplane, as the possibility of controlling perpendicular magnetic anisotropy (PMA) opens the door to the implementation of high density magnetic memory devices [12,13]. Actually, in some cases, magnetic anisotropy appears to be sensitive to lattice distortion and point towards promising spintronic applications based on the ability to control magnetic properties through modification of strain conditions. It has been proved in several material systems that t...