Magnetoresistance in ballistic nanocontacts and its manipulation in electrodeposited nanometric Ni contacts

We report comprehensive experimental studies on ballistic magnetoresistance (BMR) in nanocontacts of different materials. We show that BMR values >200% can be achieved in ballistic nanocontacts of ferromagnet such as nickel and cobalt whilst the nanocontacts of dirty ferromagnetic materials such as Heusler alloy exhibit very small magnetoresistance (MR) at room temperature (RT) and low applied field. The reason for this is that, the BMR is a nonadiabatic process, but in the dirty cases the domain wall (DW) thickness X is larger than the mean free path l for spin reversal hence the electrons can adiabatically follow the magnetization change when they traverse the DW resulting in negligible DW scattering. We also show that in an electrodeposited stable nanoscopic nickel contact it is possible to manipulate the MR by applying current pulses and external magnetic field. We discuss the origin of this effect in terms of combined effect of current induced and external field.