| AVS 58th Annual International Symposium and Exhibition | |
| Actinides and Rare Earths Focus Topic | Wednesday Sessions |
| Session AC+MI-WeA |
| Session: | Magnetic and Electron Correlation Effects in Actinides and Rare Earths |
| Presenter: | Ladislav Havela, Charles University, Czech Republic |
| Authors: | L. Havela, Charles University, Czech Republic N.-T. Kim-Ngan, Pedagogical University Cracow, Poland A. Adamska, Charles University, Czech Republic A.G. Balogh, TU Darmstadt, Germany T. Gouder, European Commission, JRC Institute for Transuranium Elements, Germany |
| Correspondent: | Click to Email |
Actinide-based sputter deposited films were so far used in the context of surface-science studies (such as [1]) and for exploration of electronic structure by photoelectron spectroscopy (e.g. [2,3]). In addition, sputter deposition was used in attempts to synthesize amorphous uranium alloys for ex-situ studies of magnetic properties. Such early (late 1980's) attempts in U.S. [4] or Japan [5] were undertaken in simple setups and lack proper diagnostics of the deposited material. Considering strong electropositivity of U, oxidation has to be suspected for films prepared in HV conditions. More recently, U metal in multilayers with possibility of epitaxial growth were sputter deposited with the aim to induce uranium magnetic moments [6]. We have used sputter deposition to investigate structure and magnetic properties of various U-based compounds as a function of deposition conditions (deposition rate, substrate type and temperature). Employing diagnostics by XPS, Glancing Angle XRD, and RBS, it was established that UN films have a long-term stability, which allows comfortably to make ex-situ studies over months. The reason can be seen in pronounced compressive residual strains, imposed during the deposition, which prevent progressing the surface oxidation into the bulk of several hundred nm thick films. Departing more from a fully crystalline state, the antiferromagnetism of UN is masked by a weak ferromagnetism, as usual for nanograined AF structures, and finally both moments and their order disappears [7]. Similar suppression of magnetism was found for ferromagnetic US [8].
Recently we undertook sputter-deposition experiments on Fe-rich U-Fe alloys derived from the Laves phase UFe2, which combines the 3d and 5f magnetism in a compound with a relatively high Curie temperature (TC = 162 K). An Fe-excess is expected to increase the TC value markedly. Nanocrystalline material obtained up to the stoichiometry UFe2.3 by splat cooling, with the excessive Fe atoms entering the U sublattice has TC enhanced up to 230-240 K. More Fe leads to the segregation of α-Fe. We succeeded to synthesize amorphous films by U and Fe co-sputtering, with stoichiometry up to UFe3. TC is enhanced up to 450 K in this case.
[1] T. Gouder et al., Surface Science 601 (2007) L77.
[2] T. Gouder et al., Phys.Rev.Letters 84 (2000) 3378.
[3] L. Havela et al., Phys.Rev.B 65 (2002) 235118.
[4] P.P. Freitas et al., J.Appl.Phys. 63 (1988) 3746.
[5] S. Itoh et al., Physica B 281-282 (2000) 230.
[6] R. Springell et al., Phys. Rev. B 77 (2008) 064423.
[7] D. Rafaja et al., J.Alloys Comp. 386 (2005) 87.
[8] L. Havela et al., J. Alloys Comp. 408-412 (2006) 1320.