Magnetic excitations in a new anisotropic Kagom\'{e} antiferromagnet

The Nd-langasite compound contains planes of magnetic Nd3+ ions on a lattice topologically equivalent to a kagom\'{e} net. The magnetic susceptibility does not reveal any signature of long-range ordering down to 2 K but rather a correlated paramagnetism with significant antiferromagnetic interactions between the Nd and a single-ion anisotropy due to crystal field effect. Inelastic neutron scattering on Nd-langasite powder and single-crystal allowed to probe its very peculiar low temperature dynamical magnetic correlations. They present unusual dispersive features and are broadly localized in wave-vector Q revealing a structure factor associated to characteristics short range-correlations between the magnetic atoms. From comparison with theoretical calculations, these results are interpreted as a possible experimental observation of a spin liquid state in an anisotropic kagom\'{e} antiferromagnet.Comment: to appear in Physica

Structure and defect characterization of multiferroic ReMnO3 films and multilayers by TEM

International audienceEpitaxial rare earth manganite thin films (ReMnO3; Re = Tb, Ho, Er, and Y) and multilayers were grown by liquid injection metal organic chemical vapor deposition (MOCVD) on YSZ(111) and the same systems were grown c-oriented on Pt(111) buffered Si substrates. They have been structurally investigated by electron diffraction (ED) and high resolution transmission electron microscopy (HRTEM). Nanodomains of secondary orientation are observed in the hexagonal YMnO3 films. They are related to a YSZ(111) and Pt(111) misorientation. The epitaxial film thickness has an influence on the defect formation. TbO2 and Er2O3 inclusions are observed in the TbMnO3 and ErMnO3 films respectively. The structure and orientation of these inclusions are correlated to the resembling symmetry and structure of film and substrate. The type of defect formed in the YMnO3/HoMnO3 and YMnO3/ErMnO3 multilayers is also influenced by the type of substrate they are grown on. In our work, atomic growth models for the interface between the film/substrate are proposed and verified by comparison with observed and computer simulated images

Oxides heterostructures for nanoelectronics

International audienceWe summarise in this paper the work of two groups focusing on the synthesis and characterisation of functional oxide for nanoelectronic applications. In the first section, we discuss the growth by liquid-injection MOCVD of oxides heterostructures. Interface engineering for the minimisation of silicate formation during the growth of polycrystalline SrTiO(3) on Si is first presented. It is realised via the change of reactant flow or chemical nature at the Si Surface. We then report on the epitaxy on oxide substrates of manganites films and superlattices and on their magnetic and electrical properties. La(0.7)Sr(0.3)MnO(3) and La(0.8)MnO(3-delta) as well as multiferroic hexagonal ReMnO(3) manganites are considered. We show that the film thickness and related strain may be used to tune the properties. Finally, we demonstrate the growth of MgO nanowires by CVD at a moderate temperature of 600 degrees C, using gold as a catalyst. In the second section, we discuss the growth of epitaxial oxide heterostructures by MBE. First, the direct epitaxy of SrTiO(3) on Si is considered. Issues and control of the SrTiO(3)/Si interface are discussed. An abrupt interface is achieved. We show that SrTiO(3) on Si can be used as a buffer layer for the epitaxy of various perovskite oxides such as LaAlO(3) or La(0.7)Sr(0.3)MnO(3). La(0.7)Sr(0.3)MnO(3), films are ferromagnetic and metallic at room temperature. The epitaxial growth of complex oxides on Si waters opens Lip the route to the integration of a wide variety of functionalities in nanoelectronics. Finally, we discuss the monolithic integration of III-V compounds Such as InP on Si using epitaxial SrTiO(3) buffer layers for the future integration of optics on Si

Thin films and superlattices of multiferroic hexagonal rare earth manganites

International audienc

Stability of High Temperature Chemical Vapor Deposited Silicon Based Structures on Metals for Solar Conversion.

International audienc

Magnetic Frustration on a Kagomé Lattice in R3_{3}Ga5_{5}SiO14_{14} Langasites with R = Nd, Pr

9 pages. 1 table, 5 figures.International audienceIn the R$_{3}$Ga$_{5}$SiO$_{14}$ compounds, the network R of rare earth cations form well separated planes of corner sharing triangles topologically equivalent to a kagomé lattice. Powder samples and single crystals with R = Nd and Pr were prepared and magnetostatic measurements were performed under magnetic field up to 10 T in the temperature range from 1.6 K to 400 K. Analysis of the magnetic susceptibility at the high temperatures where only the quadrupolar term of the crystal electric field prevails, suggests that the Nd and Pr magnetic moments can be modeled as coplanar elliptic rotators perpendicular to the three fold axis of the crystal structure that interact antiferromagnetically. Nonetheless, a disordered phase that can be ascribed to geometric frustration persists down to the lowest temperature which is about 25 times smaller than the energy scale for the exchange interactions

Nanodomains in multiferroic hexagonal RMnO3 films (R = Y,Dy,Ho,Er)

International audienceA homogeneous distribution of ferroelectric nanoinclusions was observed by optical second harmonic generation in epitaxial films of hexagonal RMnO3 (R = Y, Dy, Ho, Er) grown on ZrO2(Y2O3) substrates. The inclusions correspond to secondary orientations in the c-axis-oriented films. Their volume density is in the range of 10(-3) and their occurrence is independent of growth technique and film thickness in the range of 20-1000 nm. The inclusions behave as preferentially polarized ferroelectric nanodomains whereas the epitaxial film is in a ferroelectric single-domain state. In addition, the antiferromagnetic phase exhibits nanodomains of < 100 nm which is three orders of magnitude below the extension of bulk antiferromagnetic domains in RMnO3. Indications for a polarization-induced magnetic order different from that of the bulk are discussed