Ballistic magnetoresistance in nickel single-atom conductors without magnetostriction

Large ballistic magnetoresistance (BMR) has been measured in Ni single-atom conductors electrodeposited between microfabricated thin films. These measurements eliminate magnetostriction related artifacts. By making measurements on single atom conductors, the benchmark for the incontrovertible evidence against magnetostriction is set at the unyielding condition of the known quantum mechanical principles, namely, 1G _o =2e ²/h=1/12 900 Ω ^-1 (for ferromagnetic contacts the unit of conductance being 1/2G _o=1/25 800Ω ^-1) is the universal threshold ballistic conductance of an unbroken single atom contact below which even an angstrom separation of the contact due to magnetostriction is immediately signaled by an abrupt and large increase in tunneling resistance of several hundred thousand ohms across the gap. The present approach to electrodeposited point contacts between microfabricated thin films also provides an independent confirmation of Garcia's original BMR experiments on atomic point contacts that were made by a mechanical method [N. Garcia, M. Munoz, and Y.-W. Zhao, Phys. Rev. Lett. 82, 2923 (1999)]. There are many intricacies and subtleties to be resolved and understood in the highly interesting BMR phenomenon. Conclusive elimination of magnetostriction related artifacts, which is most easily invoked as a primary alternative explanation to the electronic origin of BMR, is one step towards a better understanding of these atomic scale entities. In addition, several explanations of null effects in some of the reported literature are given.