Epitaxial GdN/SmN-based superlattices grown by molecular beam epitaxy
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Epitaxial GdN/SmN-based superlattices grown by molecular beam epitaxy Franck Natali1, Joe Trodahl1, Stéphane Vézian2, Antoine Traverson1, Benjamin Damilano2, and Ben Ruck1 1
The MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Chemical and Physical Sciences, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand 2
Université Côte d’Azur, Centre de Recherche sur l’Hétéro Épitaxie et ses Applications (CRHEA), Centre National de la recherche Scientifique (CNRS), France ABSTRACT GdN/SmN based superlattices have been grown by molecular beam epitaxy. In-situ reflection high energy electron diffraction was used to evaluate the evolution of the epitaxial growth and the structural properties were assessed by ex-situ X-ray diffraction. Hall Effect and resistivity measurements as a function of the temperature establish that the superlattices are heavily n-type doped semiconductors and the electrical conduction resides in both REN layers, SmN and GdN. INTRODUCTION The rare earth (RE) atoms are the fourteen elements following lanthanum in the periodic table. In recent years RE-based thin films (i.e. layers with thickness less than 1Pm), either REoxides, silicides or nitrides have emerged as structures and materials of choice for microelectronic, nanoelectronic, and spintronic applications. The rare earth nitrides (REN) films grown in the last few years have extremely rare properties, with most combining the properties of both ferromagnets and semiconductors; they are intrinsic ferromagnetic semiconductors,[1] though the potential for heavy doping by nitrogen vacancies leave the assignment of stoichiometric RENs as semiconductors or metals uncertain.[2] Their strongly spin-split bands [1,3] offer in principle the possibility to control independently the doping and the magnetism opening not only new possibilities for spintronics devices and fundamental spin transport. Intensive magnetic studies on bulk REN layers or REN-based superlattices have shown, for example, a magnetisation in direct opposition to the spin moments or ferromagnetically aligned spins accompanied by no net magnetization [4,5,6,7] highlighting their potential for magnetic tunnel junctions or memory elements. The magnetic contrast is especially strong between the magnetically soft magnetic behaviour of the strong magnetisation in GdN and the enormously hard, near-zero magnetisation of SmN. These are exactly the contrasts required for memory elements. Here we present early results on the epitaxial growth, structural and electrical properties of SmN/GdN superlattices. EXPERIMENT The growth of SmN/GdN superlattices was performed by MBE on 100 nm thick (0001) AlN buffer layers grown on silicon (111) substrates. Prior to the growth of the superlattices, the AlN surface was cleaned using a thermal annealing at 880°C under ammonia (NH3) for 15 min.
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