Memory of magnetic nanowires
doi:10.1038/nindia.2010.119 Published online 31 August 2010
New research has shown that a small magnetic field can trigger unique magnetic behaviour in cylindrical nickel nanowires. This behaviour could be used to design memory devices for data storage.
Nickel nanowires are ferromagnetic, a magnetic ordering in which the spins of unpaired electrons align together in a region called a domain, which is bound by domain walls.
When a current or magnetic field is applied to a ferromagnetic wire, the domain walls move along the length of the wire. This induced motion could be the basis for a memory device in which information is stored in magnetic domains.
Although domain wall motion has been observed in manganese-doped semiconductor epilayers, scientists had yet to demonstrate a clear signature of the magnetic-field-driven random walk of domain walls in magnetic nanowires. To achieve this, the researchers electrochemically grew nickel nanowires in anodic alumina templates, placed the nanowires on silicon oxide substrates and then exposed the nanowires to a small magnetic field. The domain walls were found to move in a Brownian manner along the length of the nanowires with the external drive of the magnetic field.
The researchers attached voltage probes to the nanowires for measuring fluctuations in electrical resistance, which signalled the presence or absence of one or more domain walls between the voltage probes. The random fluctuation in electrical resistance is sensitive to domain wall motion at very small length scales.
This is the first experimental evidence of the random walk of domain walls in magnetic nanowires with cylindrical geometry. The researchers say that domain walls in a magnetic nanowire could form the building block of a random access memory.