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Friday, May 17

Exploring the Crystal Structure, Magnetism, and
Magnetoresistance of Epitaxial Perovskite Films

Tricia Meyer, The Ohio State University , Columbus
Materials Science and Technology Division Seminar
1:30 PM — 2:30 PM, Chemical and Material Sciences Building (4100), Room J-302
Contact: Ho Nyung Lee (hnlee@ornl.gov), 865.574.9782

Abstract

The chemically disordered solid solution, CaxSr1-xMn0.5Ru0.5O3, has proven to be an interesting demonstration of the effects of chemical pressure. The end member, SrMn0.5Ru0.5O3, exhibits a cooperative Jahn-Teller (JT) distortion corresponding to the occupied Mn3+ dz2-orbitals along the c-axis.

Substitution of Sr2+ with small Ca2+ increases the tilting of the RuO6 and MnO6 octahedra, disrupting the JT distortion and hence orbital ordering. This results in a transition from an antiferromagnetic insulator to a metallic ferromagnet. The sensitivity of this system to orbital ordering provides an excellent opportunity to explore these properties in epitaxial films grown via pulsed laser deposition (PLD). An investigation of the structural, transport, and magnetoresistive properties of several different compositions of this solid solution has been achieved. In addition, a discussion of the impact of varying oxygen partial pressure during growth of SrMn0.5Ru0.5O3 films and lattice mismatch in CaMn0.5Ru0.5O3 films will also be presented.

Unlike the disordered CaxSr1-xMn0.5Ru0.5O3 perovskites, the structural, magnetic, and transport properties of the double perovskite, Sr2FeMoO6, are highly dependent upon the ordering of the Fe and Mo cations. Though not as widely discussed in film literature, maintaining stoichiometry of the Fe, Mo, and Sr cations during growth is just as essential as maximizing the ordering so that the best properties may be obtained. Therefore, we have systematically investigated the stoichiometry and ordering of Sr2FeMoO6 films and the resulting effects upon the properties. This was achieved by tuning PLD growth parameters such as substrate-to-target distance, temperature, and pressure and completing comprehensive Rutherford backscattering, x-ray diffraction, and magnetic measurements on the films.