Asymmetric Hysteresis Loops of Systems of Bistable Nanoscopic Wires

Abstract

A system of bistable magnetic nanowires of diameter D = 57 nm, length L = 115 nm, magnetization M = 370 emu/cm3 is simulated. The probability distribution of the switching fields of the wires is Gaussian, with mean Hs = 710 Oe and standard deviation u(Hs) = 105 Oe. The wires are randomly distributed on a plane, with directions parallel (OX) or perpendicular (OY) to the axis direction where the magnetic field is applied. The magnetostatic interaction between the wires leads to an asymmetry of the hysteresis loop of the system. Namely, we obtain different curves M(H) for ascending and descending magnetic field. This behaviour is due to the wires which are perpendicular to the applied magnetic field. The directions of their magnetic moments remain often unchanged during the hysteresis experiment, and their contribution to the magnetic moment measured along OX is equal to zero. However, they interact with the wires parallel to the field, and this interaction influences the magnetic state of the parallel wires. The effect can be useful when we are interested in tailoring the shape of the hysteresis loop. Also, a given magnetic configuration of the wires parallel to OY produces a unique asymmetry of the hysteresis loop of the wires parallel to OX. Once an additional field is applied along OY, this unique state is destroyed. The effect can be useful for safety systems.

Simulated hysteresis loop of a bent Fe-rich glass-covered wire

“…As a consequence, the inner core is shifted to the convex part, and the compressive bending stress in the concave part of the wire produces a strong anisotropy perpendicular to the wire axis, which destroys the bistability. We conclude that bent wires offer more options of spatial configurations, as ordered and random arrays [24,25], and therefore enable new opportunities of applications.…”

Gardens of Eden in systems of bistable nanoscopic wires

“…This kind of memory enables construction of a magnetic key for single use only. In our previous paper [20], we noted that asymmetric hysteresis loops of the wire sets can be used for similar purposes, but the property of irreversibility seems to fit even better as a method of authentication. On the other hand, our numerical results can serve as a model description of small dots of magnetic gels with nanoparticles ( [21] and references therein).…”