Number 816, March 23, 2007
by Phil Schewe and Ben Stein
The conversion of a tiny magnetic flux into a change in the resistance of an external circuit, a process called magnetoresistance, is at the heart of the $60-billion magnetic hard-disk-drive industry. Digital data, stored on the disk in the form of minuscule polarizations (representing a 1 or a 0) on the disk in tiny domains only 50 by 200 nm in size, are read out by a sensor flying only 10 nm overhead.
The first unambiguous observation of a digital version of the magnetoresistance effect-the change in the resistance recorded by the sensor changes in discrete steps as the magnetization orientation relative to the sensor is changed-is hereby reported by physicists from the University of Nebraska (US) and the Institut de Physique et de Chimie des Materiaux de Strasbourg (France).
The quantization of conductance on the sensor side was achieved by having the current flow through a constriction that tapers down to the size of a single atom (see figure at www.aip.org/png), a passage which imposes quantum conditions. According to Nebraska scientist Andrei Sokolov (email@example.com), an atom-sized point contact makes the read-write process ever more compact in physical extent, allowing much greater data storage. (Sokolov et al., Nature Nanotechnology, March 2007; http://www.nature.com/nnano/index.html)
Data Links Transmitting and Receiving at Unprecedented Rates
A new IBM transceiver, an integrated device which can transmit and receive record-breaking amounts of high-speed data in optical form, has been developed. The transmitting part of the device consists of 16 vertical cavity surface emitting lasers (VCSELs), lasers that emit light from the face of a semiconductor chip rather than from the cleaved edge of the chip. Each laser is capable of modulating a continuous laser beam at a rate in excess of 10 billion times per second (a record for individual devices in a transceiver), for a total data-sending rate of 160 Gigabits per second (Gb/s).
The 16-channel receiving part of the device operates at the same speed, for a simultaneous data-receiving rate of 160 Gb/s. The optical channels carrying the data can be either fibers or optical waveguides printed on a circuit board. Not only is the single-channel data rate unprecedented, but the power dissipation (15.6 mW/Gb/s) and the density (9.4 Gb/mm^2) are also unprecedented and key figures of merit. IBM is developing this transceiver as part of a Defense Advanced Research Projects Agency (DARPA)-sponsored chip-to-chip program designed to speed up communications between supercomputers.
Clint Schow of IBM will announce details of this work at next week’s Optical Fiber Conference (OFC) in Anaheim, California. (http://www.ofcnfoec.org/; Paper OThG4, “160-Gb/s, 16-Channel Full-Duplex, Single-Chip CMOS Optical Transceiver”)
More Ozone Was Destroyed
More ozone was destroyed by an 1859 solar flare than any similar event recorded since, such as the great flare of 1989. No satellites were around to measure that occurrence, but new evidence presents itself in the form of Greenland ice samples.
These samples reflect the arrival of solar protons, which help to break up ozone, which in turn modulates the amount of nitrates showing up in ice samples. Upper atmospheric ozone helps protect us from the sun’s ultraviolet glare. The contribution of humanmade chemicals to the destruction of this precious ozone, and the widening of the “ozone hole,” has been naturally a topic of great concern.
The new study was undertaken by three scientists, one at Washburn University, one at NASA Goddard, and one at the University of Kansas. The sampled ice core allowed the scientists to determine that the 1859 solar flare was some 6.5 times more energetic than the 1989 flare and 3.5 times more destructive of ozone. (Thomas, Jackman, Mellott, Geophysical Research Letters, March 2007)