Extraordinary Magnetoresistance of InSb Allows Fabrication of a Read-Head Sensor without Magnetic Noise
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excellent method for designing the large synthetic arrays necessary to bridge the gap between small-molecule and macromolecule DNA-recognition motifs. Absorption, nuclear magnetic circular dichroism, and flow linear dichroism spectra showed that while both the M and P enantiomers of [Fe2L3]4+ bind strongly to DNA, their binding modes and structural effects are very different; the first binding mode of the M enantiomer is along the major groove, and the P enantiomer most likely binds in the minor groove, according to the researchers. Molecular-level images obtained with atomic force microscopy are consistent with these binding modes and provided visual evidence of the induced DNA bending/coiling. The M enantiomer kinks and coils DNA substantially more than the P enantiomer, whose effect was significant but much less dramatic. The coiling had little effect on the local structure of the base-base interactions, a characteristic in common with molecules that serve to package DNA into chromosomes. In current studies, Rodger and Hannon are derivitizing the M-enantiomer backbone in order to optimize the hydrogenbonding and steric effects in the major groove. Rodger and Hannon anticipate that tuning sequence selectivity into the backbone of the M enantiomer will enable them to target specific sequences to be coiled. STEVEN TROHALAKI
Extraordinary Magnetoresistance of InSb Allows Fabrication of a Read-Head Sensor without Magnetic Noise Read-head sensors are one of the main devices for data recording and storage in hard-disk drives. These sensors are commercially manufactured from magnetic materials with properties such as giant magnetoresistance (GMR) or tunneling magnetoresistance (TMR), and therefore are subject to magnetic noise. As a consequence, the use of read heads based on GMR and TMR is limited to areal densities of the order of 100 Gb/in.2. However, the extraordinary magnetoresistance (EMR) exhibited by nonmagnetic narrow-gap semiconductors such as InSb is free of magnetic noise and represents an alternative for a new class of read-head sensors that are compatible with large capacity storage. A group of scientists from the NEC Research Institute in Princeton, N.J., the NEC Fundamental Research Laboratories in Japan, and the University of Oklahoma joined efforts under the guidance of NEC Institute’s Stuart Solin to take advantage of the EMR properties of InSb to fabricate a mesoscopic read-head sensor, as they explained in the May 27 issue of Applied Physics Letters. 494
EMR appears as a consequence of a magnetic-field-induced deflection of current around a patterned metallic inhomogeneity present in or on the boundary of a semiconductor. A narrow-gap semiconductor with high-mobility carriers such as InSb shows this property in films thicker than 1 µm. Read-head sensors require thinner films of ≤100 nm. Since carrier mobility in InSb decreases dramatically for thicknesses below 1 µm, this group of scientists designed a quantumwell structure to fabricate a mesoscopic sensor within the targeted thickness with a high
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