Magnetic structures of permalloy film microspots

Abstract

The present day interest in micron and submicron magnetic objects is stimulated, in particular, by their possible applications in computer engineering [1][2][3][4] and biomedicine [5,6]. In the majority of publica tions, of concern is the problem of film disk shaped spots. For reasonably small sizes of a disk, the mag netic vortex is formed with circular magnetization in the spot plane on the periphery and with the magneti zation outcrop from the plane in the center (the vortex core). The magnetic interaction of two or more vorti ces is many times less intense than the interaction of uniformly magnetized magnetic cells of the same shape and volume, which makes it possible to decrease the sizes of spots with the vortex structure and, thus, considerably increase the information density in the medium. In dependence on the direction of core mag netization (conditionally upwards or downwards), one distinguishes the positive and negative vortex polariza tions and the direction of the magnetic flux closure of the vortex flat part determines its chirality (right or left). The store of information (0 or 1) in a cell with the vortex magnetic structure is possible in two ways: according to the sign of polarization and according to the type of chirality (right or left). The purpose of this investigation is to study the effect of sizes and shapes of a spot on its magnetic structure and to clarify the prac tical prospects of spots of different shape-square and triangular in addition to circular. EXPERIMENTAL EQUIPMENTAND RESULTS Permalloy film spots of 30-60 nm thick with trans verse sizes from 20 to 1 µm were the object of investi gation. The samples were made by photolithography from a continuous film obtained by the method of vac uum condensation of vapors of an initial material (permalloy Ni 80 Fe 20 ) on a glass substrate. For the Lorentz microscopy, the metal vapors were deposited on a substrate (formvar) transparent to the electron beam through a grid with square cells. The magnetic structures were visualized with the help of a VEECO multimode III magnetic force microscope, an UEMV 100A electron microscope, and an MBI 6 optical microscope (using a FER 01 diluted ferrofluid as the magnetic suspension).In Fig. 1, we show the patterns of magnetic struc tures characteristic for permalloy spots of circular, square, and triangular shape. In the case of circular spots of 5 µm in diameter and smaller in the thickness range of 30-50 nm, a steady equilibrium structure of the classical magnetic vortex with a central core arises. For square spots, it is a structure with a closed mag netic flux (quasi vortex) composed of four domains with the magnetization oriented along the adjoining side of the square that is equilibrium; the domains are separated with an approximately 90 degree Néel boundaries and with the Bloch point (quasi core) in the structure center. It is characteristic for all investi gated sizes of the spot and film thicknesses. In the case of triangular spots, the quasi vortex with a quasi core is also formed, but the sp...

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“…С. С. Замай 1 , В. С. Прокопенко 1,3 , А. С. Замай 1,2 , В. В. Денисенко 1,4,5 , П. Д. Ким 1 , В. А. Орлов 1,3,4 , Г. С. Замай 1,2 , Т. И. Иванченко 1 , Т. Н. Замай 2,4 1 Красноярский научный центр СО РАН, Председатель -академик РАН В. Ф. Шабанов; лаборатория биомагнитных материалов и биосенсоров, руководитель -д. ф.-м. н., проф.…”

“…В случае круглого нанодиска с вихревой магнитной структурой (пермаллой, кобальт) дипольный момент обеспечивается намагниченностью небольшой части диска, его ядра, то есть центральной части диска с намагниченностью, перпендикулярной плоскости нанодиска -центральная тёмная точка на рисунке 3а. На рисунке 3 показаны снимки магнитных структур [2], характерных для пермаллоевых нанопластин круглой (a), квадратной (b) и треугольной (c) формы.…”

Features in the Resonance Behavior of Magnetization in Arrays of Triangular and Square Nanodots

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