Tailoring magnetoresistance through rotating Ni particles

We present \textit{ab initio} studies for different Ni nanocontacts and show changes in the conductance of such constrictions due to atomic rearrangements in the contact. In particular we consider a Ni particle and show that the magnetoresistance can change from a few to 50% and can even reverse sign as a function of the contact area formed between the particle and the leads.