arXiv subjects

R. J. Reeves

Publications and source records attributed to R. J. Reeves.

4 recordsLinked to original sources

arXiv2017

Indications of spin polarized transport in Ba$_2$FeMoO$_6$ thin films

We have investigated the magnetic and magnetotransport properties of Ba$_2$FeMoO$_6$ thin films produced by pulsed laser deposition from optimized bulk material. The films are comprised of grains of crystalline Ba$_2$FeMoO$_6$ with a disordered grain boundary region that lowers the net saturation magnetization of the film and prevents full magnetic alignment below a Curie temperature $T_C$$\sim$305 K. Magnetotransport measurements point to the Ba$_2$FeMoO$_6$ grains retaining the high spin polarization of a half-metal up to $T_C$, while the grain boundaries greatly reduce the spin polarization of the intergrain electrical current due to spin-flip scattering. Our results show that a strong spin polarization of the electronic charge carriers is present even in Ba$_2$FeMoO$_6$ films that do not show the ideal bulk magnetic character.

cond-mat.mes-hall↗

arXiv2011

The observation of electron trap liberation in MgF$_{2}$ doped with Yb$^{2+}$ using a two-color excitation experiment

We utilize the optical transitions of Yb$^{2+}$ excited by an ultraviolet optical parametric amplifier to probe electron trap liberation in MgF$_{2}$ via the observation of a photoluminescence enhancement effect induced by a subsequent infrared pulse from a free-electron laser. The temperature dependence of the enhancement suggests that we liberate very shallow traps having a depth of approximately 17 cm$^{-1}$. The observed `trap spectrum' is consistent with a simple model of a Coulomb trap.

cond-mat.mtrl-sci↗

arXiv2011

Impurity-trapped excitons and electron traps in CaF$_2$:Yb$^{2+}$ and SrF$_2$:Yb$^{2+}$ probed by transient photoluminescence enhancement

CaF$_2$:Yb$^{2+}$ and SrF$_2$:Yb$^{2+}$ crystals have been investigated by a two-color UV + IR transient photoluminescence enhancement technique. The enhancement gives information about both changes in internal energy levels of the excitons and liberation of electrons from traps in the crystals.

cond-mat.mtrl-sci↗

arXiv2005

The unusual temperature dependence of the Eu$^{2+}$ fluorescence lifetime in CaF$_2$ crystals

Fluorescence lifetimes of Eu$^{2+}$ doped in CaF$_2$ are measured at various temperatures between 4K and 450K. The lifetime increases with between 100K and 300K, in contrast to the usual lifetime-temperature dependence. At higher or lower temperatures the lifetime decreases with increasing temperature. The phenomenon is explained by simulation of the energy levels and lifetimes of low-lying $4f^65d$ states involved in the fluorescence.

cond-mat.mtrl-sci↗