Photodarkening experiments have been performed on evaporated films of Gel Sn Se2 in the composition range 0& x ~0.60 at 78 K. Thermal cycling between room temperature and 78 K was observed to reduce the optical absorption of the films. The photodarkening response is slightly enhanced at x =0.1 but is suppressed for higher Sn concentrations.Chalcogenide glasses such as amorphous GeSe2, As2S3, and similar compounds display an intriguing property known as "photodarkening. " %'hen exposed to light of energy near or above the band gap, they undergo a
It waa discovered that the application of a constant DC field (-lo4 Vhm) at m m temperature for several days reversed the changes in the electrical properties produced by thermal annealing in Ca:YIG single crystal f h s . The electrical conductivity of these f h s improved by fwe to seven orders of magnitude during this process to values aa much as ten times greater than those of the as-grown state. After the field was removed this new high conduction state waa found to be atable. The rate of conductivity increase became exponentially smaller when either the applied field or the temperature were decreased.
The existence of an in-plane anisotropy in the room-temperature electrical resistivity of an (011)-oriented liquid-phase-epitaxy-grown Ca0.14:yttrium iron garnet (YIG) film has been observed. The resistivity determined along the [01̄1] crystal direction was found to be consistently larger than that along the [100] direction by a factor of 1.47±0.07, which is within 4% of the square root of 2. These results suggest that charge conduction may in fact be occurring entirely along the easy 〈100〉 directions regardless of the crystal orientation of the applied electric field. The observed preference for a conduction path along the [100] direction is discussed in terms of linear chains of alternating {Y}–O–(Fe)–O–{Y} ions which are known to extend through the entire macroscopic length of the YIG crystal.
Ca-substituted YIG samples, Y3−xCaxFe5O12−0.5x−z for 0.14≤x≤0.23 were annealed for 6–8 h at various temperatures between 600 °C and 1000 °C in N2 atmosphere. The magnetization barely shows any change by annealing under 900 °C but by annealing between 900 °C and 1000 °C a significant change over the temperature range from 4.2 K to the Curie temperature is observed. The lattice constant is also observed to change. The magnetization and the lattice constant of the samples did not change within experimental error by annealing in O2 atmosphere at 1000 °C. For the sample with x=0.23, annealing at 1000 °C in N2 resulted in a decrease of 4πM at 4.2 K by 560 G and a decrease of the lattice constant by 0.031 Å. The Curie temperature also changes from 531 K in the as-grown sample to 508 K for this annealing condition. The change in 4πM for various annealing conditions is linear with the change in the lattice constant. For the samples tested, the oxygen vacancies, z, in the as-grown state shows z≳0 and that z did not change by annealing in O2 atmosphere. A microscopic molecular field model based on the Heisenberg Hamiltonian in which a singly charged oxygen vacancy, VȮ, mediates a ferromagnetic superexchange between the iron ions at adjacent sites is proposed. The model explains the temperature dependence of 4πM, the magnitude of superexchange constant mediated by VȮ and the variation of the Curie temperature with annealing conditions. This model also explains the positive slope of 4πM at low temperature for Ca-substituted YIG.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.