Fletcher Werner

Spin glassiness and power law scaling in anisotropic triangular spin-1/2 antiferromagnets

We present data on the magnetic properties of two classes of layered spin S=1/2 antiferromagnetic quasi-triangular lattice materials: Cu2(1?x)Zn2x(OH)3NO3(0?x?0.65) and its long-organic-chain?intercalated derivatives Cu2(1?x)Zn2x(OH)3(C7H15COO)?mH2O(0?x?0.29), where non-magnetic Zn substitutes for Cu isostructurally. It is found that the intercalated compounds, even in a clean system in the absence of dilution, x=0, show spin glass behaviour, as evidenced by DC and AC susceptibility, and by time-dependent magnetization measurements. A striking feature is the observation of a sharp crossover between two successive power law regimes in the DC susceptibility above the freezing temperature. In constrast to standard theoretical expectations, these power laws are insensitive to doping. Specific heat data are consistent with a conventional phase transition in the unintercalated compounds, and glassy behaviour in the intercalated compounds.

Photo effects at the Schottky interface in extraordinary optoconductance

Non-uniform optical illuminations near the Schottky interface of Ti/GaAs metal-semiconductor hybrid (MSH) structures induce local photovoltages transverse and lateral to the interface. In these VLSI-compatible, room temperature optical sensors, the optical response of the MSH resistance is directly linked to the Schottky barrier behavior. In order to correlate the interface behavior with the overall heterostructure behavior, quantities such as transverse photovoltage, lateral photovoltage, and resistance are all recorded as a function of laser spot location. The interfaces photovoltaic dependence on intensity is consistent with a MSH in which quantum efficiency is independent of optical intensity.

Shunt-Enhanced, Lead-Driven Bifurcation of EEC Sensor Responsivity

We report the observed bifurcation in extraordinary electroconductance (EEC) sensor response to direct reverse bias based on measurement lead location as well as a dramatic enhancement in responsivity achieved via a modification of the shunt geometry. A maximum percent change in the four-point resistance of 130856% was achieved under a direct reverse bias of -1 V using an enhanced shunt design, a 325 fold increase over the conventional EEC square shunt design. This result was accompanied by an observed bifurcation in sensor response, driven by a rotation of the four-point measurement leads.