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The authors report ferromagnetism at room temperature in Co doped CeO2−δ thin films grown by pulsed laser deposition on SrTiO3 and Si substrates. On SrTiO3 ceria is epitaxied and displays a high crystalline quality. On Si the films are textured with a dominant orientation. While the ferromagnetism is little affected by the amounts of structural defects, it depends sensitively on the oxygen pressure during growth and annealing. This indicates that oxygen vacancies could be involved in the magnetic coupling between Co ions. Furthermore, the epilayers grown on SrTiO3 display a large magnetic anisotropy with an out of plane easy axis.

We studied the structural, chemical and magnetic properties of non-doped ceria (CeO(2)) thin films electrodeposited on silicon substrates. Experimental results confirm that the observed room temperature ferromagnetism is driven by both cerium and oxygen vacancies. We investigated ceria films presenting vacancy concentrations well above the percolation limit. Irradiation experiments with neon ions were employed to generate highly oxygen defective CeO(2-δ) structures. X-ray photoelectron spectroscopy and x-ray absorption near-edge structure spectroscopy were used to estimate the concentration of Ce(3+) sites in the films, which can reach up to 50% of Ce(3+) replacing Ce(4+), compared to a stoichiometric CeO(2) structure. Despite the increment of structural disorder, we observe that the saturation magnetization continuously increases with Ce(3+) concentration. Our experiments demonstrate that the ferromagnetism observed in ceria thin films, highly disordered and oxygen-deficient, preserving the fluorite-type structure only in a nanometer scale, remains intrinsically stable at room temperature.

The reaction of natural chrysotile fibers with phenylphosphonic acid leads to a new grafted material. The layered material, with an interplanar basal distance of 15.2 A ˚, was characterized by powder X-ray diffraction, thermal analysis, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy and energy dispersive X-ray analysis. The experimental data are consistent with the grafting of phenylphosphonate groups to the surface of the layered silica sheets, obtained by the in situ acidic leaching of brucite sheets, from chrysotile.

By using heteroepitaxy on two different GaAs templates, we have investigated the impact of anisotropic strain on the magnetocaloric effect (MCE) of MnAs. The temperature range, spread around room temperature, and the maximal MCE position are markedly different in the two epitaxial systems. Simulated MCE curves, obtained from a model based on the mean-field approximation, are in good agreement with the experimental data, indicating that the entropy variation is magnetic in origin. These results illustrate how strain can be used to tune the MCE in materials with coupled structural and magnetic phase transition and suggest that the MCE of MnAs may find applications in microelectronic circuitry.

We have studied the magnetic and magnetotransport properties of Fe/Cu mu1tilayers prepared by sputtering. We find oscillations of the inter1ayer coupling as a function of the Cu thickness with the same long period as in Co/Cu multilayers (around 12.5 Á). The most striking result is that the oscillations in Fe/Cu and Co/Cu have almost exactly opposite phases. A large magnetoresistance of the spin-valve type is observed in the half periods with antiferromagnetic interlayer exchange. However, the magnetoresistance in Fe/Cu is definitely smaller than in Co/Cu.In this paper we report on magnetoresistance and magnetization measurements on Fe/Cu multilayers prepared by sputtering. As in Co/Cu multilayers we have previously studied, 1 we find a long-period oscillation of the interlayer exchange as a function of the copper thickness and a large magnetoresistance (MR) in the thickness ranges where this exchange is antiferromagnetic.There are now several examples of multilayered systems exhibiting an oscillatory interlayer exchange and a large magnetoresistance arising from the so-called spin-valve effect. Fe/Cr, 2 -6 Co/Ru, 4 Co/Cr, 4 and Co/Cu (Ref. 1) are the best known systems. For the interlayer exchange, the most puzzling result is the long period of the exchange oscillations. Values between 12 and 21 Â are found, which is much longer than expected from the simple Ruderman-Kittel-Kasuya-Yosida (RKKY)-like models and have generated a large number of theoretical models. 7 An oscillatory behavior of the interlayer exchange, coupled with oscillations of the Kerr effect, has also been recently found by Bennet, Schwarzacher, and Egelhoff 8 in Fefcc(001)/Cu/Fefcc(001) sandwiches grown on Cu(IOO). Our present results on Fe/Cu multilayers prepared by sputtering confirm these oscillations. The period is practically equal to that found in Co/Cu, that is about 12.5 Â. 1 However, a puzzling and interesting result is that the oscillations in Co/Cu and Fe/Cu have opposite phases; in other words, the coupling between Fe layers is antiferromagnetic (AFM) in the thickness ranges where the coupling between Co layers is ferromagnetic (FM) and vice versa. The Fe/Cu system also exhibits a spinvalve effect in the AFM half periods but the magnetoresistance is smaller than in Co/Cu and does not exceed 12%.Samples of 60x (15-Â Fe/tcu Cu) multilayers have been deposited on Si(IOO) substrates in a UHV compatible sputtering system 9 at Michigan State University. A 50 Â buffer layer of Fe is first deposited on the substrate and the top layer is always a 50 Â layer of Cu. The experimental methods for the characterization of the samples, and the magnetic and magnetoresistance measurements have been described in our previous publication. 1 In addition we have performed extended x-ray-absorption finestructure (EXAFS) measurements 10 at both the F e and Cu K edges using the facilities at the Laboratoire pour l'Utilisation du Rayonnement Electromagnétique (LURE) at Orsay. Preliminary results indicate that the structure of the Fe layers is clearly bcc. ...