Dipolar interactions in arrays of iron nanowires studied by Mossbauer spectroscopy

We have performed numerical calculations and experimental studies on the dipole-dipole interaction in the hexagonal nanowire arrays. Using the dipole approximation with a length correction, the dipolar fields in the cylindrical wire arrays were calculated. By means of Mossbauer spectroscopy, the dipolar fields in the Fe nanowire arrays fabricated by anodic porous alumina template-grown method were derived from the relationship between effective hyperfine field and applied field. Both the theoretical predictions and experimental results show there is a rather strong dipolar field with the saturation field perpendicular to the wire axis, while the dipolar interaction with magnetic moment aligned along the wire axis is too weak to be taken into account. The easy magnetization direction is determined by a competition of the dipolar interaction and the shape anisotropy. The critical ratio between the diameter of nanowire and the distance between nanowires, on which the easy axis of nanowire arrays would be changed from parallel to perpendicular to the wire axes, was calculated.