Jennifer Soliz

The effect of chemical pressure on the structure and properties of A 2 CrOsO 6 (A=Sr, Ca) ferrimagnetic double perovskite

The ordered double perovskites Sr2CrOsO6 and Ca2CrOsO6 have been synthesized and characterized with neutron powder diffraction, electrical transport measurements, and high field magnetization experiments. Sr2CrOsO6 and Ca2CrOsO6 crystallize with R-3 and P21/n space group symmetry, respectively. Both materials are found to be ferrimagnetic insulators with saturation magnetizations near 0.2 {\mu}B. Sr2CrOsO6 orders at 660 K, showing non-monotonic magnetization temperature dependence, while Ca2CrOsO6 orders at 490 K and does not show non-monotonic behavior. Evidence for a theoretically predicted canted magnetic structure in Sr2CrOsO6 is sought and not found.

Electronic and magnetic tunability of Sr2CrReO6 films by growth-mediated oxygen modulation

Highly ordered epitaxial films of ferrimagnetic semiconductor Sr2CrReO6 (SCRO) have been fabricated by off-axis magnetron sputtering, and characterized as a function of the oxygen partial pressure. In this Letter, we report 18 000% modulation in electrical resistivity at T = 7K (60% at room temperature) from a 1% modulation in the oxygen partial pressure during film growth. The growth window was centered at peak saturation magnetization, which drops due to both increasing and decreasing oxygen growth pressure. The results suggest that n-type doping due to oxygen vacancies plays a dominant role in the electrical properties and modulation of Sr2CrReO6 thin films.

Buffer-layer enhanced structural and electronic quality in ferrimagnetic Sr2CrReO6 epitaxial films

Highly ordered epitaxial Sr2CrReO6 films of 20-nm and 175-nm thicknesses were deposited on SrTiO3 and (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates and Sr2CrNbO6 buffer layers. Electronic measurements and scanning transmission electron microscopy images clearly show that the Sr2CrNbO6 buffer layers facilitate Cr/Re ordering near the interface, thus minimizing the number of defect states in the films. Arrhenius fits of the resistivity data give activation energies of 7.3–32 meV for films grown on non-buffered substrates, suggesting defect states are more conducting than Sr2CrReO6, whereas films grown on the Sr2CrNbO6 buffer layer have activation energies in the narrow range 38.6–42.1 meV.