Angular dependence of coercivity and remanence of Ni nanowire arrays and its relevance to magnetoviscosity

Ni nanowire arrays with varying wire dimensions (diameter d, length l) and center-to-center distances d_CC were synthesized by pulsed electrodeposition of Ni in porous Al templates. The magnetization-reversal behavior of the arrays was investigated by means of magnetometry for different angles θ between the wire axes and the applied magnetic field. The functional dependences of the characteristic parameters coercivity H_C(θ) and reduced remanence m_R/m_S(θ) exhibit a strong dependence on the wire dimensions and the center-to-center distance. For instance, for nanowire arrays with d=40 nm, d_CC=100 nm, and for θ=0°, the coercivity takes on a rather large value of μ₀H_C=85 mT and m_R/m_S≅94%; reducing d_CC to 30 nm and d to 17 nm results in μ₀H_C=49 mT and m_R/m_S≅57%, an observation which suggests an increasing magnetostatic interwire interaction at increased (d/d_CC)-ratio. The potential application of nanowires as the constituents of ferrofluids is discussed.