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G. van Tendeloo

Publications and source records attributed to G. van Tendeloo.

5 recordsLinked to original sources
arXiv2014

Commensurate structural modulation in the charge- and orbitally-ordered phase of the quadruple perovskite (NaMn$_3$)Mn$_4$O$_{12}$

By means of synchrotron x-ray and electron diffraction, we studied the structural changes at the charge order transition $T_{CO}$=176 K in the mixed-valence quadruple perovskite (NaMn$_3$)Mn$_4$O$_{12}$. Below $T_{CO}$ we find satellite peaks indicating a commensurate structural modulation with the same propagation vector q =(1/2,0,-1/2) of the CE magnetic order that appears at low temperature, similarly to the case of simple perovskites like La$_{0.5}$Ca$_{0.5}$MnO$_3$. In the present case, the modulated structure together with the observation of a large entropy change at $T_{CO}$ gives evidence of a rare case of full Mn$^{3+}$/Mn$^{4+}$ charge and orbital order consistent with the Goodenough-Kanamori model.

cond-mat.str-el↗
arXiv2013

Defect engineering in oxide heterostructures by enhanced oxygen surface exchange

The synthesis of materials with well-controlled composition and structure improves our understanding of their intrinsic electrical transport properties. Recent developments in atomically controlled growth have been shown to be crucial in enabling the study of new physical phenomena in epitaxial oxide heterostructures. Nevertheless, these phenomena can be influenced by the presence of defects that act as extrinsic sources of both doping and impurity scattering. Control over the nature and density of such defects is therefore necessary, are we to fully understand the intrinsic materials properties and exploit them in future device technologies. Here, we show that incorporation of a strontium copper oxide nano-layer strongly reduces the impurity scattering at conducting interfaces in oxide LaAlO3-SrTiO3(001) heterostructures, opening the door to high carrier mobility materials. We propose that this remote cuprate layer facilitates enhanced suppression of oxygen defects by reducing the kinetic barrier for oxygen exchange in the hetero-interfacial film system. This design concept of controlled defect engineering can be of significant importance in applications in which enhanced oxygen surface exchange plays a crucial role.

cond-mat.mtrl-sci↗
arXiv2008

Direct observation of nanometer-scale pinning sites in (Nd$_{0.33}$,Eu$_{0.20}$,Gd$_{0.47}$)Ba$_2$Cu$_3$O$_{7-δ}$ single crystals

We report on the observation of self-organized stripe-like structures on the as-grown surface and in the bulk of (Nd,Eu,Gd)Ba$_2$Cu$_3$O$_y$ single crystals. The periodicity of the stripes on the surface lies between 500 and 800 nm. These are possibly the growth steps of the crystal. Transmission electron microscopy investigations revealed stripes of periodicity in the range of 20 to 40 nm in the bulk. From electron back scattered diffraction investigations, no crystallographic misorientation due to the nanostripes has been found. Scanning tunneling spectroscopic experiments revealed nonsuperconducting regions, running along twin directions, which presumably constitute strong pinning sites.

cond-mat.supr-con↗
arXiv2006

A-site Ordering versus Electronic Inhomogeneity in CMR-Manganite Films

Epitaxial La3/4Ca1/4MnO3/MgO(100) (LCMO) thin films show unusual rhombohedral (R-3c) structure with a new perovskite superstructure due to unique ordering of La and Ca at the A-site positions. Very sharp insulator-metal and para-ferromagnetic phase transitions at temperatures up to TMI ~ TC=295 K were observed. The ordered films were electronically homogeneous down to 1 nm scale as revealed by scanning tunnelling microscopy/spectroscopy. In contrast, orthorhombic and A-site disordered LCMO demonstrate broadened phase transitions as well as mesoscopic phase separation for T<<TC. The unique La/Ca ordering suppresses cation mismatch stress within one super-cell, a~1.55 nm, enhancing electronic homogeneity. Phase separation scenario seems not to be a unique mechanism for CMR as very large CMR=500 % was also observed in A-site ordered films.

cond-mat.str-el↗