Stability of Ferromagnetic Patterns Inscribed on Arrays of Multisegmented Magnetic Nanocylinders

Abstract

Magnetic nanocylinders (MNs) can be grown inside of longitudinal nanoporous produced in alumina membranes by means of different techniques. In a similar way, multisegmented MNs (m-MNs) can be obtained by alternating magnetic and nonmagnetic materials during the fabrication process. In both cases, nanocylinders result axially parallel and forming triangular arrays immerse themselves within the membrane used to produce them. Due to shape anisotropy, each magnetic segment presents its magnetization pointing along the cylinder axis either inward or outward of the membrane plane. The as-grown system presents no global magnetization. A strong enough localized magnetic field can revert the magnetization of small groups of neighboring m-MNs. This feature can be used to inscribe ferromagnetic patterns (FP) over either membrane surface to store fixed information (security codes or firmware). Here, we study the total energy per cylinder for the case of a disc shaped FP inscribed over a circular membrane containing a huge amount of m-MNs. To try to prevent spontaneous magnetization reversion due to thermal effects we test for m-MNs a stabilization mechanism proposed previously for homogeneous MNs: an opposite ferromagnetic band (OFB) inscribed inside the FP. We have compared inscription and stabilization of FP over arrays of homogenous and multisegmented MNs.