No abstract

Bipolar resistance switching was investigated on sputtered Pr0.7Ca0.3MnO3 (PCMO) sandwiched by Pt- and Ti-electrodes. Based on electrical conductivity measurements and a combination of electron energy loss spectroscopy analysis and transmission electron microscopy observation, we found that the negative differential resistance observed in the forming process originates from the motion of oxygen ions at the Ti/PCMO interface. We propose that the observed resistance switching is caused by an oxidation/reduction reaction at the interface.

Faraday rotation and ellipticity spectra were measured at photon energies hv = 0.9-4.0 eV for R3 +$!e,Fes012 (R = Y, Gd, Yb) films with substitutions up to x = 2.5, expitaxially grown by rf sputtering. The Ce substitution prominently enhances the Faraday effect not only in the IR region at hv = 1.4 eV but also in the UV region at hv = 3.1 eV. Both transitions have a paramagnetic dispersion relation, which are nearly equal in magnitude but opposite in sign. Optical absorption is also induced by a new transition due to Ce" + at hv = 2.1 eV, which does not enhance Faraday rotation. These electronic transitions may be attributed to charge transfer transition Ce3 + (4J)-Fe3 + (tet.) .

Cerium substituted yttrium iron garnet films epitaxially grown by rf diode sputtering were found to have exceptionally large Faraday rotation in the visible and near infrared (1–2 eV). Faraday rotation at room temperature is enhanced in proportion to Ce content by a factor per Ce ion of 2×104 deg/cm for λ=633 nm and -1.3×104 deg/cm for 1150 nm. The latter factor is 5 times higher than that by Bi. The Ce-substituted YIG films are the most promising magneto-optical materials.

We found that Pr0.7Ca0.3MnO3 (PCMO) film sandwiched by a Ta top electrode (TE) and a Pt bottom electrode (BE) exhibited bipolar resistance switching similar to that of Ti(TE)/PCMO/Pt(BE). The switching capability of Ta/PCMO/Pt was greatly improved by pulse-forming compared to dc-forming, which are both pre-treatments to enable resistance switching by pulsed voltage. Switching speeds faster than 100 ns and rewrite cycles of more than 10,000 were obtained while maintaining a ratio of resistance change larger than 1,000%. The mechanism of resistance switching was explained by an oxidation/reduction reaction at the Ta/PCMO interface, as previously proposed for Ti/PCMO/Pt.