Kevin Roche

Magnetically engineered spintronic sensors and memory

The discovery of enhanced magnetoresistance and oscillatory interlayer exchange coupling in transition metal multilayers just over a decade ago has enabled the development of new classes of magnetically engineered magnetic thin-film materials suitable for advanced magnetic sensors and magnetic random access memories. Magnetic sensors based on spin-valve giant magnetoresistive (GMR) sandwiches with artificial antiferromagnetic reference layers have resulted in enormous increases in the storage capacity of magnetic hard disk drives. The unique properties of magnetic tunnel junction (MTJ) devices has led to the development of an advanced high performance nonvolatile magnet random access memory with density approaching that of dynamic random-access memory (RAM) and read-write speeds comparable to static RAM. Both GMR and MTJ devices are examples of spintronic materials in which the flow of spin-polarized electrons is manipulated by controlling, via magnetic fields, the orientation of magnetic moments in inhomogeneous magnetic thin film systems. More complex devices, including three-terminal hot electron magnetic tunnel transistors, suggest that there are many other applications of spintronic materials.

Temperature and bias dependence of magnetoresistance in doped manganite thin film trilayer junctions

Thin film trilayer junction of La0.67Sr0.33MnO3-SrTiO3-La0.67Sr0.33MnO3 shows a factor of 9.7 change in resistance, in a magnetic field around 100 Oe at 14 K. The junction magnetoresistance is bias and temperature dependent. The energy scales associated with bias and temperature dependence are an order of magnitude apart. The same set of energies also determine the bias and temperature dependence of the differential conductance of the junction. We discuss these results in terms of metallic cluster inclusions at the junction-barrier interface.

Improved laser technique for high sensitivity atomic absorption spectroscopy in flames

Abstract Frequency modulation laser spectroscopy is utilized for high sensitivity detection of trace species aspirated into a flame of the type commonly used for atomic absorption spectroscopy (AAS). The method is applied to the detection of sodium atoms in an air-acetylene flame and data are obtained on the distribution of ground and excited state populations as a function of height above the burner. Absorptions as small as 1.5 × 10 -4 may be detected with a signal-to-noise of one. With multi-passing, a detection limit of 3.3 × 10 6 sodium atoms/cm 3 was obtained.