Topographic anisotropy in continuous magnetic films with two-dimensional surface nanomodulation

Abstract

Artificial and local control of spin-configuration in nanoscale in continuous magnetic films could enable new spin-based electronics and precision sensor technologies. Extensive theoretical research has recently been devoted to examination of surface nanovariation mediated magnetism and its utility, which has been demonstrated only in one-dimensional surface modulation. However, a realization of engineered spin configuration using two-dimensional (2D) nanomodulation is limited by local vortex formation induced by magnetostatic energy. In this work we demonstrate for the first time, an ability to control the anisotropy in continuous magnetic films by periodic surface nanomodulation in two-dimensions (2D). Magnetic properties of NiFe films with nanomodulated surfaces have been studied as a function of both film thickness and modulation amplitude. For films with a patterned square array (without breaking the film continuity), a clear fourfold symmetry of anisotropy field and coercivity was observed with rotation angle. An experimental phase diagram of anisotropy with respect to film thickness and modulation amplitude has been produced which delineates that the observed fourfold anisotropy is induced by the magnetostatic effect. The observed dependence of anisotropy field on film thickness and surface modulation amplitude agrees well with the developed theory. (C) 2010 American Institute of Physics. [doi:10.1063/1.3501111

Manipulation of Magnetic Properties by Tunable Magnetic Dipoles in a Ferromagnetic Thin Film

“…For a square array pattern of 400-nm diameter and 100-nm modulation the energy density of vortex 0.49×10 4 J/m 3 is lower than energy of single domain state 1.33×10 4 J/m 3 . [Li 2010, Maity 2012] Hence there will be a natural tendency to adopt vortex state in this modulated film to minimize the energy. Here the competition between two different dipoles (in-plane and out-of-plane) and possible spin pinning between two consecutive dipoles through continuous ferromagnetic media keeps the magnetization stable in the direction of applied field and resists vortex formation.…”

“…[Li 2010, Li 2011] The three dimensional structure of the patterned ferromagnetic Ni45Fe55 thin film has been delineated by AFM imaging ( Fig. 1 b & c).…”

Characteristics and controllability of vortices in ferromagnetics, ferroelectrics, and multiferroics

“…For composition-graded films and layer structural composite films, the composition should be carefully controlled during the film growth process. While planar films have been extensively grown and studied, also noteworthy are those with surface modulation [133,134,[160][161][162]. Films with surface modulation can be obtained by using patterned substrates or templates, or using lithography techniques after the growth of uniform films.…”

Ordered magnetic dipoles: Controlling anisotropy in nanomodulated continuous ferromagnetic films

“…1(d)] was prepared by an electrodeposition process 15 on patterned substrates fabricated by nanoimprint lithography. 5 A polymethylmethacrylate (PMMA, molecular weight ∼230 k) layer of 1 μm thick was spin-coated on a cleaned, 0.5-mm-thick silicon substrate and baked at 100 • C for 10 min in air. Two different silicon stamps with 400/400-and 200/200-nm diameter/separation (D/S) were used to create square arrays of nanoholes.…”

“…In recent years, this has been demonstrated for patterned isolated magnetic structures [2][3][4] and structured continuous magnetic films. 5,6 Such kinds of control open up opportunities for potential applications, such as spintronic devices, magnetic random access memory (MRAM), 7 high-density patterned information storage media, 7,8 and high-precision ultra-small magnetic field sensors. 9 Due to fundamental reasons and potential applications, it is necessary to understand further the magnetic properties of patterned structures in reduced dimensions, while both geometry and crystal microstructure need to be optimized prior to configuring the magnetization.…”