Magnetic properties of square Py nanowires: Irradiation dose and geometry dependence

Abstract

Arrays of ferromagnetic patterned nanostructures with single particle lateral dimensions between 160 nm and 400 nm were created by electron-beam lithography. The fourfold particles with rectangular-shaped walls around a square open area were produced from permalloy. Their magnetic properties were measured using the longitudinal magneto-optical Kerr effect. The article reports about the angle-dependent coercive fields and the influence of the e-beam radiation dose on sample shapes. It is shown that a broad range of radiation dose intensities enables reliable creation of nanostructures with parameters relevant for the desired magnetization reversal scenario. The experimental results are finally compared with micromagnetic simulations to explain the findings. V C 2015 AIP Publishing LLC. [http://dx.

Influence of shape and dimension on magnetic anisotropies and magnetization reversal of Py, Fe, and Co nano-objects with four-fold symmetry

“…This finding is well-known from theoretical and experimental examinations of fourfold Py nanostructures in different dimensions. 25 In the open square geometry, the samples of smaller dimensions show the angle dependent coercivities which are usual fourfold anisotropies, while the maximum vanishes more and more for larger samples. Apparently, the differences between hard and easy axes become blurred if the samples are larger.…”

“…1 shows the different shapes which were used for simulations with lateral dimensions of 50 nm, 100 nm, 200 nm, and 400 nm. While the larger values are typical in recent lithographic approaches, 25 the smallest one is meant to give an outlook to the possibilities of future lithographic or other patterning techniques.…”

Influence of the Distance between Nanoparticles in Clusters on the Magnetization Reversal Process

“…The particles under simulation here had slightly different geometries ( Figure 1): one of them, defined as "square corner cuts," has an ideal structure which has shown to lead to two additional intermediate states at remanence [5], while the other one, denoted as "diagonal corner cuts," has a more realistic shape, as recognized in former lithographically produced nanostructures [19,20]. Lateral dimensions of each nanoparticle were 120 nm in the sample plane and 5 nm height, corresponding to the smallest samples used in former experimental investigations [19,20]. This value was chosen since the aim of this study is to find the highest possible particle density and thus the highest data density.…”

Magnetization Reversal in Ferromagnetic Nanorings of Fourfold Symmetries

“…Nanostructures of two different geometries were chosen for simulation ( Figure 1): one square ring with "ideal" square corner cuts which has shown to result in intermediate stable states at remanence [16] and one ring with "realistic" diagonal corner cuts which was gained in former lithographic processes [17,18]. Lateral dimensions were chosen as 200 nm diameter and 5 nm height, similar to real nanorings under experimental investigation [17,18].…”

“…In several situations, hysteresis loops with steps on both sides occur in theoretical and experimental investigations, allowing creating "quaternary" memory systems with four stable states at vanishing external magnetic field and thus the possibility of storing two bits in one position [16]. On the other hand, experimental investigation of these structures has revealed undesired modifications of the original rings' shapes in the lithography process, resulting in modified magnetization reversal processes [17,18]. This experience underlines the necessity of examining the influence of such shape modifications to allow creation of nanorings with reliable magnetic properties.…”