Magnetization reversal in nano triangles
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Magnetization reversal in nano triangles X.H. Wang1, S. Goolaup1. C.X.Cong1 and W.S. Lew1, 1 School of Physical and Mathematical Sciences, Nanyang Technological University, 637371, Singapore INTRODUCTION Thin film ferromagnetic nanostructures are of considerable interest because of their potential applications in ultrahigh-density recording media and spintronic devices1, 2. For optimum performance of these devices, understanding and controlling the magnetic properties of individual and interacting elements at reduced dimension plays a key issue. Different patterned magnetic nanostructures like rectangles3, dots4 and rings5 have been investigated. Recently, the magnetization reversal mechanisms in sub-100 nm sized patterns have attracted a lot of attention due to the requirement of density increase in the developing recording technology. In nanomagnets with size in this sub-100 nm range, the shape anisotropy becomes important to the magnetization reversal. Using conventional lithography techniques, such as electron beam lithography6, interference lithography7, as well as x-ray lithography, magnetic patterns in hundred nm size range have been studied. However, in conventional lithography techniques, the proximity effect in the e-beam and focused ion beam may lack shape definess in these length scales, leading to a rounded corner in square or triangle dots. Nanosphere lithography (NSL) is a well-known, low-cost, and quick preparation method, which makes use of self-assembly of nanospheres to fabricate nanostructure and nanostructure arrays. Various shapes of nanostructures, such as triangulars, hexagonals, rings, and chains, have been obtained by different ways through NSL. Using NSL, Niu et al8 demonstrated that the nanoscale magnetic dots with the size approaching the superparamagnetic limits could have an enhanced coercivity. Magnetic asymmetric rings are also fabricated via NSL assisted with oblique angle ion beam etching by Zhu et al9 to study the switching process. In this work, we have carried out a systematic study of the magnetization reversal process in triangular dots fabricated by NSL. Triangular shape nanomagnets with different lateral sizes were patterned over an area of over 30 um2. The magnetic properties of the nanomagnets were characterized using MOKE. We observed that the magnetic properties of the triangular nanomagnets are markedly sensitive to the lateral dimensions of the structures. Our experimental results were substantiated using micromagnetic simulation. A good agreement was obtained between the experimental and theoretical results. II EXPERIMENTAL DETAILS Monodispersed nanospheres with diameter of 465 nm and 365 nm in a suspension of 2.6wt% in water, surfactant-free, were diluted by mixing with an equal amount of ethanol. The schematic of the fabrication process is shown in Fig 1(a). The Si substrates were first cleaned first with acetone and then followed by, ethanol. About 5 uL of the prepared solution was dropped onto the
surface of a 3cm * 3 cm large clean silicon wafer. T
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