Size dependence of the magnetic properties of electrochemically self-assembled Fe quantum dots

A quasi-periodic array of Fe quantum dots of cylindrical shape has been synthesized by electrodeposition of Fe in porous alumina. By controlling the fabrication parameters, we have controlled the length, diameter, and spacing of the dots. The magnetic properties are shown to depend on these parameters. It has been found that at room temperature, there exists a critical diameter of the dots for which the coercivity is a maximum. The largest value of coercivity obtained at room temperature is 2640 Oe which rises to 2900 Oe an annealing. At a low temperature of 5K, an increase in coercivity is observed for most of the samples. The largest value is 3800 Oe which rises to a value of 4100 Oe in the corresponding annealed counterpart. At 5K, no maximum is seen in the coercivity as a function of diameter. Instead, the coercivity is found to decrease with increasing diameter. This dependence of the coercivity on diameter is discussed in terms of localized reversal effects.