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1. Current-induced and Photoinduced Changes inBi1-xCaxMnO3 Thin Films Vera SmolyaninovaDMR-0348939 V V I I illuminated region Doped rare-earth manganese oxides (manganites) exhibit a wide variety of physical phenomena due to complex interplay of electronic, magnetic, orbital, and structural degrees of freedom and their sensitivity to external fields. A photoinduced insulator-to-conductor transition in charge-ordered (CO) manganitesis especially interesting from the point of view of creating photonic devices. We have found that 50 nm Bi0.4Ca0.6MnO3 thin film grown on NdCaAlO4 (NCAO) substrate is very susceptible to increase of current and illumination with argon-ion laser light (λ ~ 500 nm). Application of these stimuli partially destroys charged ordering and produces charge-disordered conductive phase (Fig. 1). Combined application of illumination and current completely destroys the charge ordering in this material, while the application of one of these factors separately is not sufficient to produce such effect. This results in decrease of resistivity by more than two orders in magnitude at low temperatures. The I-V curves are nonlinear and hysteretic and depend on history with respect to application of current (Fig. 2), which is related to appearance of a new conducting phase produced by increased current. Above the CO temperature there are no current-induced and photoinduced effects (Figs. 1 and 2). Such properties of these materials potentially could be used in opto-electronic switches. These results are published in PRB 76, 104423 (2007). (a) (b) Fig. 2. Voltage-current dependencies for the Bi0.4Ca0.6MnO3 thin film grown on (001) oriented NCAO substrate with illumination (blue) and without illumination (red) for different temperatures: (a) T = 100 K; (b) T = 250 K. The sample was current biased. Fig. 1. (a) Temperature dependence of the resistivity of the Bi0.4Ca0.6MnO3 thin film grown on (100) oriented NCAO substrate. Red: I = 10-5 A; blue: I = 10-4 A; green: I = 10-3 A; dashed lines – the sample was illuminated. (b) Experimental current and voltage contact configuration with respect to illuminated region.

2. Education and OutreachVera SmolyaninovaDMR-0348939 Towson University is an undergraduate institution with strong emphases on undergraduate research. Two Towson students, Gene Vanmeter and Khim Karki, and one College of Notre Dame (local college, which does not have a research program) student Kim Wall were involved in this research. Gene Vanmeter and Khim Karki presented the results of their research at the Student Research and Scholarship Expo and College of Science and Mathematics Honors Convocation, Towson University (2007). PI participated in the REU/RET (Research Experience for Undergraduate/Teachers at Towson) as a mentor for a teacher/undergraduate student team. High school teacher Robert Kennedy and undergraduate student from Allegany College Kevin DeMarchi had an opportunity to study photoinduced effects in manganese oxides with various experimental techniques. PI and her students are collaborating with the director of the newly formed Hackerman Academy, former NASA astronaut Don Thomas in his quest to promote science and engineering among high school students. High school science teacher R. Kennedy and Towson undergraduate students K. Karki are pre-cooling a superconducting magnet.