Tuning Nanohole Sizes in Ni Hexagonal Antidot Arrays: Large Perpendicular Magnetic Anisotropy for Spintronic Applications

Abstract

Perpendicular magnetic anisotropy (PMA) in transition metal thin films offers a pathway for enabling the interesting physics of nanomagnetism and developing a wide range of spintronics applications. We demonstrate a simple method to obtain Ni thin films with PMA by depositing them onto nanoporous anodic alumina membranes (NPAAMs), with different pore diameters varying in the range between 32 ± 2 and 93 ± 1 nm. Thus, several sets of Ni antidot arrays thin films have been fabricated with different hole diameters, 35 nm ≤ d ≤ 89 nm, and fixed interhole distances, D int , around 103 ± 2 nm but reducing the edge-to-edge separation between adjacent antidots, (W = D int − d), and in two different situations, by considering that W is well above or below the layer thickness, t, of the thin film. The crossover from the in-plane magnetization to out of plane magnetization in a ferromagnetic thin film has been achieved by modifying only the nanopore size of the patterned anodic alumina template and the experimental results were supported by micromagnetic simulations performed with Mumax 3 code. A dramatic change in the coercivity, H C , dependence with d and W parameters has been observed with a critical nanohole diameter, d c , at which the appearance of the perpendicular magnetization is observed. The decreasing of the inplane coercivity for samples with d > 75 nm is due to the weakened of the in-plane magnetic anisotropy and the rising of the out of plane component. The effective perpendicular magnetic anisotropy energy density for Ni antidot thin film with d = 90 nm and t = 20 nm is around 1.44 erg/cm 2 , larger than that obtained by traditional approaches for Ni films with PMA (0.03−0.2 erg/cm 2 ). These findings point toward antidot thin films as novel routes to engineer the magnetic behavior of ferromagnetic metal with large PMA, which might entail a milestone for future applications in bit patterned magneto-optic perpendicular recording media and spintronic devices.

Revisiting anodic alumina templates: from fabrication to applications

“…This approach may be applied to high-density storage data systems and spintronic logic devices. Also, they can act similarly as photonic crystals do for photons, exhibiting a periodic potential for magnons and where the spin-wave dispersion can be tuned for the fabrication of spin filters and spin waveguides 295 . Some magnetic behavior arises from commonly non-magnetic bulk materials when reducing the dimensionality of the system, such in the case of 2D antidot films.…”

Optical and Electrochemical Characterization of Nanoporous Alumina Structures: Pore Size, Porosity, and Structure Effect

“…Nanoporous alumina structures (NPASs) obtained by electrochemical anodization of aluminum foils according to the two-step anodization method [1,2] are of great interest due to their application as nanofilters, drug deliverers, templates for nanoparticles, nanotubes, nanowires, platforms for sensors, and medical devices [3][4][5][6][7][8][9]. Lately, other applications of NPASs such as spintronics, solar cells, light emitting diodes, and photonic crystals have been studied [10][11][12][13][14][15][16]. Most of these applications are related to the high structural regularity of NPAS, which exhibit almost ideal cylindrical pores with narrow pore radius distribution and without tortuosity, but their thermal and chemical resistance are also of great interest when used as nanofilters or membranes due to their stability under cleaning protocols commonly used to reduce fouling (adsorption/deposition of transported molecules or particles), which is the main problem in such applications [17,18].…”

Influence of nanoholes array geometrical parameters on magnetic properties of Dy–Fe antidot thin films

“…The deposition rate of the Dy-Fe alloy was around 0.1-0.15 nm s −1 . The experimental details about the deposition conditions have been already reported elsewhere[8,35].…”

“…higher than the critical point of the geometrical parameter, the effective in-plane local magnetic anisotropy becomes weaker because of the increasing contribution of intrinsic magnetic anisotropy of the continuous thin film area between the adjacent holes.Therefore, different magnetic anisotropy contribution and symmetry appeared. It is known, that the coercivity of the antidot arrays thin film is determined as a balance between the intrinsic magnetic anisotropy of thin film and the shape anisotropy induced by the arrays of holes[35,36,38]. If we now choose the macroscopic, or non-local configuration for the laser beam of the NanoMOKE-3 magnetometer, the area of sample surface covered by the laser beam has a diameter of the order of 0.5 mm.…”