A nanoscale, nonmagnetic read-head

A Nanoscale, Nonmagnetic Read-head sensor, based on extraordinary magnetoresistance (EMR), has been developed. Today’s state-of-theart magnetic recording delivers about 15 gigabits per square inch of recording medium. To achieve that result, the read head uses magnetic metals in a layered structure with either the giant magnetoresistance (GMR) or tunneling magnetoresistance (TMR) effect to convert the field orientation (up or down) of tiny magnetic domains into changes in electrical resistance. Both effects make use of electrons’ spin and are subject to magnetic noise. By contrast, EMR makes use of electrons’ orbital degrees of freedom; the magnetic fields deflect a current from a conducting shunt attached to the semiconductor and thereby produce resistance changes. A group led by Stuart Solin of NEC Research Institute in Princeton, New Jersey, has now used nonmagnetic, silicon-doped indium antimonide to build a mesoscopic read head (see the scanning electron micrograph) that operates on the EMR principle. According to Solin, GMR and TMR will ultimately have a noiselimited areal density of about 150 Gb/in², whereas EMR could reach 1 Tb/in² and has a fast enough response time to utilize that density. The researchers fabricated their 116-Gb/in² device using a multistep electron-beam lithography process that required excruciating accuracy: Features needed to be aligned to within 10 nm. Although free of magnetic-noise limitations, the device needs to sense magnetic fields that are 10 times stronger than those sensed with current technologies, which could limit its practical application for the time being. (S. A. Solin et al., Appl. Phys. Lett. 80, 4012, 2002 http://dx.doi.org/10.1063/1.1481238 .)