LEED Fe3O4 on STiO3

Growth of iron oxide on Ru(0001)

We are now devoting a fair amount of our time to study metal oxides. Why? Metal oxides are a family of materials that provide a wide range of physical scenarios. They show rich phase diagrams reflecting the interplay between magnetitediverse atomic scale processes which may lead to singular properties and that places oxides among the most attractive multifunctional materials. The use of oxides is of particular interest in nanoscale technologies. The high quality growth of oxide thin films and heterostructures, when combined to the versatility of oxide properties, opens the path to a large number of applications in oxide electronics, like field effect transistors (FETs) based on the metal-insulator Mott transition, or spintronics, whose development largely relies in miniaturized oxide systems either showing half-metallicity or multiferroism.

The understanding and control of all these exotic properties constitutes at present both a challenge and a promising path to the discovery of new physical phenomena and their application in novel technologies. In order to do so, a close look at atomic scale processes is needed. However, it is difficult to disentangle the structural and electronic degrees of freedom, and their relation to other physical effects involving dynamical response, magnetism or conductivity. We aim to provide such information by obtaining insight into several fundamental problems on oxide systems combining theoretical and experimental methodologies: 

We have studied the reconstruction of the (100) surface of both volumic crystals and thin films of magnetite. We have determined that this reconstruction Wien magnetitedisappears at around 500°C (depending upon the stoichiometry of the particular sample) through a second order transition which has been simulated with an Ising model, performing predictions on the influence of the reconstruction in the character semimetallic of magnetite, and therefore in its possible use as a source of spin polarized electrons. It has also been observed for the first time both in real space and at the surface the paraelastic-ferroelastic transition of magnetite (Verwey transition), by means of both low energy electron microscopy (in collaboration with the Berkeley National Laboratory) and by STM (through a collaboration initiated with the group of Ulrike Diebold, at the Technical University of Vienna).

Molecular beam epitaxy consists on using a atomic beam of a given element generated from a doser (in our case, the doser is a metal bar heated by leem magnetiteelectron bombardement and with a water shroud to avoid heating the areas around the doser). Such method can be used to grow oxides if oxygen is supplied as a background gas during the process. One can use O2, O3 or NO2 to such end. In our case, we are using either O2 or NO2.


We have studied the initial growth stages of iron oxides on Ru (0001) by oxygen-assisted MBE. Iron oxides on metals are interesting for catalysis applications, and they have been studied quite a bit, so they are a kind of model system. On Ru, FeO grows initially, while at later stages Fe3O4 is obtained.

In collaboration with the group of Lasers, Nanostructures and Materials Processing we have initiated a intense collaboration aimed at studying the growthSTM PLD of magnetite thin films on various oxide substrates either polycrystalline (SiO2) or single crystal (SrTiO3 (100) and others). We have studied the influence that the laser wavelength and the substrate temperature during deposition have on the stoichiometry and structural quality of the films formed and we have found that wavelengths in the infrared and substrate temperatures of 450 ° C give rise to magnetite films with the correct stoichiometry and with high structural quality. In addition, we are studying the influence that the deposition parameters and the nature of the substrate exert on the magnetic anisotropy observed in the films.

We collaborate with other groups in the characterization of complex oxides:


  • With Frank Berry and collaborators from the Department of Chemistry, University of Birmingham (UK), we have synthesized and characterized new complex transition metal oxides with different structures. In particular, we have studied the magnetic properties, the oxidation state of the cations and the different structural properties of FeSb2O4, which is isostructural with Pb3O4, and some lead- and cobalt-doped variants of composition FeSb1.5Pb0.5O4 and Co0.5Fe0.5Sb1.5Pb0.5O4. We have found that antimony is present as Sb3+ and that the presence of Pb2+ on the antimony site induces partial oxidation of Fe2+ to Fe3+.The results have shown that there is no Verwey-type transition in which electrons are shared between iron in different oxidation states and that the quasi-one-dimensional magnetic structure gives rise to situations in which weakly coupled Fe2+ ions can coexist in a non-magnetic state alongside Fe3+ ions in a magnetically ordered state. Further work comprises the study initiated in previous years on the effect that the fluorination of compounds of the type Sr3Fe2O7-x exerts on the cationic distribution and the complex magnetic properties of these materials.
  • As part of a collaboration with Juan Luis Gautier and collaborators (Department of Materials Chemistry, University of Santiago de Chile), that has spread over the past fifteen years through bilateral cooperation projects we have studied compounds of composition LiNixCo2-xO4 , which are of interest in the field of Li-ion batteries, and which have been synthesized via sol gel procedures at low temperature. By means of X-ray photoelectron spectroscopy, XPS, we have found that a fraction of the Co ions in these compounds is present in the relatively unusual oxidation state of Co4+.