Effect of strain and growth morphology on the evolution of the domain structure of ferromagnetic manganites
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Effect of strain and growth morphology on the evolution of the domain structure of ferromagnetic manganites Holly Miller1,2, J. S. Higgins3, Y. Mukovskii4, R. L. Greene3, and Amlan Biswas1 1
Department of Physics, University of Florida, Gainesville, FL 32611, USA School of Engineering, University of Virginia, Charlottesville, VA 22904, USA 3 Center for Superconductivity Research, University of Maryland, MD 20742, USA 4 Moscow State Steel and Alloys Institute, Moscow, Russian Federation 2
ABSTRACT The effect of strain on the surface magnetism of the manganite La0.7Sr0.3MnO3 has been studied as a function of temperature, using magnetic force microscopy. The nonuniform strain distribution in the film leads to a two-phase coexistence between ferromagnetic and non-ferromagnetic phases. This leads to a reduction of the surface curie temperature and the formation of ferromagnetic islands. Methods of controlling this behavior in order to fabricate arrays of magnetic nanodots are discussed. INTRODUCTION The low temperature phase diagram of hole-doped manganites is dominated by two phases: a ferromagnetic metal (FMM) and an antiferromagnetic charge-ordered insulator (COI). It is well established that the competition between these two phases gives rise to the observed sensitivity of these materials to external perturbations such as magnetic and electric fields, pressure and strain [1]. The presence of these two low temperature phases with different structures leads to behavior similar to that observed in martensites [2]. In fact, there are several properties of manganites, which are also seen in purely strain-based materials such as martensites such as, hysterisis in the temperature dependence of resistivity [3]. The added feature we have in the case of manganites is that the one of the two structural phases is ferromagnetic (FM). This makes fabrication of single phase materials and devices, a major challenge. However, If we can control the strain landscape in a manganite sample we should then be able to control the size and location of the two competing phases. This gives us a unique method of fabricating magnetic nanostructures. A simple method of modifying the strain landscape is to grow thin films of these materials on lattice mismatched substrates. When a film is grown under compressive strain, it has been shown that the film grows in the form of islands and the film is under non-uniform strain [4]. The tops of the islands are relatively strain free while the edges of the islands are high-strain regions. This results in ferromagnetic regions at the top of the islands while the edges of the islands are non-ferromagnetic, possibly COI. This phenomenon was demonstrated in thin films of the compound La0.7Ca0.3MnO3 (LCMO). However, the TC of LCMO is ~250 K so the low strain regions become ferromagnetic well below room temperature. So the first question is if we can make similar FMM islands above room temperature. The obvious material choice is La0.7Sr0.3MnO3 (LSMO) since in the bulk form it has a TC ~ 350 K. However,
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