The magnetic properties of well-aligned nickel nanochains synthesized by magnetic field-induced assembly approach.

Highly uniform one-dimensional Ni chains with controllable diameters and lengths have been synthesized at 70 °C by a hydrothermal process under a 0.35 T induced magnetic field. The diameter of the spheres in the magnetic Ni chains is adjusted from 80 nm to 1000 nm with the chain length changed from 1.2 μm to 50μm by varying the concentration of ethylene glycol and potassium hydroxide in the solution. The Ni chains with different length-to-diameter aspect ratio show the different particle shape and interparticle spacing. Magnetic hysteresis loop measurements demonstrate a uniaxial magnetic anisotropy (UMA) on the coercivity (H_c), and saturation field (H_s). The ferromagnetic resonance (FMR) shows that the difference between demagnetizing fields in the direction of easy and hard increases with increasing the length-to-diameter aspect ratio of nanochains, which is close to then that in H_s. From FMR measurements and theoretical simulation, the difference of the demagnetizing field between the length and width directions of chains are obtained, which increases with increasing aspect ratio of chain. The value of the non-uniformity parameter c which describes the relative importance of the non-uniform demagnetizing effect is found to decrease as the aspect ratio increases. [ABSTRACT FROM AUTHOR]