Cationic ordering control of magnetization in Sr2FeMoO6 double perovskite

The role of the synthesis conditions on the cationic Fe/Mo ordering in Sr2FeMoO6 double perovskite is addressed. It is shown that this ordering can be controlled and varied systematically. The Fe/Mo ordering has a profound impact on the saturation magnetization of the material. Using the appropriate synthesis protocol a record value of 3.7muB/f.u. has been obtained. Mossbauer analysis reveals the existence of two distinguishable Fe sites in agreement with the P4/mmm symmetry and a charge density at the Fe(m+) ions significantly larger than (+3) suggesting a Fe contribution to the spin-down conduction band. The implications of these findings for the synthesis of Sr2FeMoO6 having optimal magnetoresistance response are discussed.Comment: 9 pages, 4 figure

Mn valence instability in La2/3Ca1/3MnO3 thin films

A Mn valence instability on La2/3Ca1/3MnO3 thin films, grown on LaAlO3 (001)substrates is observed by x-ray absorption spectroscopy at the Mn L-edge and O K-edge. As-grown samples, in situ annealed at 800 C in oxygen, exhibit a Curie temperature well below that of the bulk material. Upon air exposure a reduction of the saturation magnetization, MS, of the films is detected. Simultaneously a Mn2+ spectral signature develops, in addition to the expected Mn3+ and Mn4+ contributions, which increases with time. The similarity of the spectral results obtained by total electron yield and fluorescence yield spectroscopy indicates that the location of the Mn valence anomalies is not confined to a narrow surface region of the film, but can extend throughout the whole thickness of the sample. High temperature annealing at 1000 C in air, immediately after growth, improves the magnetic and transport properties of such films towards the bulk values and the Mn2+ signature in the spectra does not appear. The Mn valence is then stable even to prolonged air exposure. We propose a mechanism for the Mn2+ ions formation and discuss the importance of these observations with respect to previous findings and production of thin films devices.Comment: Double space, 21 pages, 6 figure

Interfacial effects in La 2/3 Sr 1/3 MnO 3 thin films with different complex oxide capping layers

Interfacial effects in sputtered La 2/3 Sr 1/3 MnO 3 thin films with different capping layers (MgO, LaAlO 3 , SrTiO 3 , NdGaO 3 , and Au) have been locally investigated by means of x-ray absorption spectroscopy and x-ray magnetic circular dichroism at the Mn L 3,2 -edge. Data were acquired by using the total electron yield detection mode thus guaranteeing maximum sensitivity to the interface. The data show that LaAlO 3 capping almost does not modify the bulklike Mn valence at the interface. In case of SrTiO 3 and Au, the presence of divalent Mn is detected, whereas MgO and NdGaO 3 capping lead to an increase of the Mn valence oxidation state. The modification of the nominal Mn valence state leads to depressed surface magnetization

Enhancement of spin orbit coupling at manganite surfaces

Spin orbit coupling in magnetic systems lacking inversion symmetry can give rise to nontrivial spin textures. Magnetic thin films and heterostructures are potential candidates for the formation of skyrmions and other noncollinear spin configurations as inversion symmetry is inherently lost at their surfaces and interfaces. However, manganites, in spite of their extraordinarily rich magnetic phase diagram, have not yet been considered of interest within this context as their spin orbit coupling is assumed to be negligible. We demonstrate here, by means of angular dependent x ray linear dichroism experiments and theoretical calculations, the existence of a noncollinear antiferromagnetic ordering at the surface of ferromagnetic La2 3Sr1 3MnO3 thin films whose properties can only be explained by an unexpectedly large enhancement of the spin orbit interaction. Our results reveal that spin orbit coupling, usually assumed to be very small in manganites, can be significantly enhanced at surfaces and interfaces adding a new twist to the possible magnetic orders that can arise in electronically reconstructed system

Exchange bias in laterally oxidized Au/Co/Au nanopillars

Au/Co/Au nanopillars fabricated by colloidal lithography of continuous trilayers exhibit and enhanced coercive field and the appearance of an exchange bias field with respect to the continuous layers. This is attributed to the lateral oxidation of the Co interlayer that appears upon disc fabrication. The dependence of the exchange bias field on the Co nanodots size and on the oxidation degree is analyzed and its microscopic origin clarified by means of Monte Carlo simulations based on a model of a cylindrical dot with lateral core/shell structure.Comment: 8 pages, 4 figures. Published in Appl. Phys. Let