Researchers question size of BMR effect
Scientists at the National Institute of Standards and Technology (NIST), US, have reported that their results do not corroborate the large changes in electrical resistance seen in ultra-small magnetic sensors. The researchers believe that, although attributed to the ballistic magnetoresistance (BMR) effect, these changes were actually due to artifacts.
According to NIST researcher William Egelhoff, reports since mid-2002 have credited the BMR effect with increases in electrical resistance ranging from a few hundred to a million per cent. But Egelhoff says these impressive changes appear to stem from artifacts. For example, two nickel wires in a T-shaped arrangement contracted on exposure to a magnetic field. This shortening could distort the cluster of atoms forming the nanoscale contact between the wires, causing a large increase in resistance. In contrast, measurements on nanocontacts between wires that did not contract in the presence of a magnetic field did not show sizeable resistance changes.
The NIST team claims to have demonstrated several other types of artifacts that can mimic electrical resistance swings corresponding to the BMR-effect values reported in scientific journals and at conferences. Now they have developed a set of recommended procedures for performing measurements in an artifact-free manner and are continuing to work on understanding the BMR effect.
The BMR effect is predicted by theory, but the ‘impressive’ results are much too large, said Egelhoff. At this point it’s inconclusive as to whether a real BMR effect will be found and, if so, whether it will prove large enough to be of much interest to the magnetic sensor community.
The BMR effect has a particular appeal to the hard-disk-drive industry as it could potentially enable an increase in the data-storage capacity of magnetic disks.
The researchers reported their findings at the American Vacuum Society’s 50th international symposium in Baltimore, US.