Magnetic properties of iron nano wire arrays: the impact of geometrical parameters

In this work, we investigated the magnetic properties of arrays of pure iron nano wires. During the study by the method of electrochemical deposition into the pores of the matrix of anodic aluminum oxide, three series of samples were synthesized. According to the data of scanning electron microscopy, the diameters of the pores (nano wires), the interpore distance, the length of nano wires, and the sizes of the structural domains were determined. It was shown that the resulting parameters are in good agreement with the data predicted during the synthesis. The data of scanning electron microscopy were used to determine the diameters of pores (nano wires), interpore spacing, length of nano wires, and sizes of structural domains. It was shown that the resulting parameters are in good agreement with the data predicted during the synthesis. Iron deposited in the pores of the anodic alumina matrix is predominantly in the α-Fe phase. Oxide components are not detected by wide-angle diffraction. It has been shown that nano wires with a diameter of about 30 nm are characterized by the presence of a predominant direction of crystallite growth along the crystallographic axis of the <110> type, while no texture was found for nano wires with a larger diameter. The data on small-angle scattering of synchrotron radiation, which are complementary to scanning electron microscopy due to the nonlocality of the method, show a good agreement between the periodicity of the structure and sizes of structural domains with the results of SEM analysis. An analysis of the first-order magnetization reversal curves, carried out for the first time for arrays of unsegmented iron nano wires, indicates the presence of nano wires oriented antiparallel in fields below the coercive force, as well as a small broadening of the distribution of the magnetization reversal fields of individual nano wires.Both the coercive force and the quadratic behavior of the magnetization reversal curves increase with the length of nano wires with a diameter of about 52 nm when an external magnetic field is applied along the long axis of the nano wires. This behavior indicates a decrease in interwire interaction, and is well described by a model that takes this interaction into account. The use of the model of magnetization reversal through the mechanism of domain wall motion showed good agreement with the results obtained using the model of interacting nano wires. This fact indicates that it is this mechanism that is dominant for arrays of such threads, and also indirectly indicates that the threads are single-domain. An additional analysis of the first-order magnetization reversal curves used in this case also indicates a decline in interwire interactions, a transition from a local character to the influence of the mean field, with an increase in the length of the nano wires, as well as behavior similar to single-domain. Using an analytical model of the magnetic behavior of arrays of magnetic nano wires, as well as micro magnetic modeling, it was found that morphological defects (texture, incomplete filling of pores, shape of ends) have a noticeable effect on the process of magnetization reversal of the nano wire. Especially, defects at the ends of nano wires play an important role, which determine the nucleation volume of inhomogeneous states. The best agreement between the experimental and calculated results was obtained for the model of 7 nano wires in the mean field approximation, which is probably due to the size and misorientation of structural domains in real arrays of nano wires. In addition, it was shown that the convergence is higher for thicker nano wires, where the volume of the inhomogeneously arising state is larger and less sensitive to morphological inhomogeneities.