Complex magnetic interactions and charge transfer effects in highly ordered Ni_xFe_1-x nano-wires

This work investigates the subtle magnetic interactions within the Ni _xFe_1-x (x=0.3, 0.5, and 1.0) nano-wires by probing spin-dependent behaviors of the two constituted elements. The wires were fabricated by electro-deposition and an anode aluminum oxide template to produce free-standing nature, and the Ni-Fe interactions were probed by x-ray magnetic spectroscopy across a BCC→FCC structural transition. The wires' magneto-structural properties were predominated by Ni, as reflected by a decrease but an increase in total magnetization and FCC x-ray intensity with increasing x, even if the Fe moment increased simultaneously. Upon annealing, a prominent charge transfer, together with the changes of spin-dependent states, took place in the Ni and Fe 3d orbitals, and a structural disordering was also obtained, for the wires at x=0.3. The charge transfer led to a local magnetic-compensation for the two elements, explaining the minor change in total magnetization for x=0.3 probed by a vibrational sample magnetometer. When x was increased to 0.5, however, the charge transfer became inactive due to persistent structural stability supported by Ni, albeit resulting in nearly invariant magnetization similar to that of x=0.3. The complexity of the Ni-Fe interactions varied with the composition and involved the modifications of the coupled magnetic, electronic and structural degrees of freedom. The study identifies the roles of Ni and Fe as unequally-influential in Ni _xFe_1-x, which provides opportunities to re-investigate the compound's properties concerning its technological applications.