Ordered magnetic nanostructures: fabrication and properties

Nanofabrication of magnetic storage media, where servo marks, discrete tracks or individual islands are defined, offer the prospect for improved performance and increased areal density. However, this increase in performance will require that new and additional processes be introduced into disk manufacturing. We review here the fundamental patterning and fabrication processes that have been proposed, along with their respective strengths and weaknesses and the potential advantages they may offer for magnetic recording. The increase in data density afforded by nanofabrication may have added significance as more conventional approaches to ever increasing density will encounter physical limitations set by the thermal stability of the recorded bits.

https://iopscience.iop.org/article/10.1088/0022-3727/38/12/R01/pdf

Nanofabricated and self-assembled magnetic structures as data storage media

http://www.cwscholz.net/projects/papers/preprint/scholz/cms03/magpar.pdf

Scalable parallel micromagnetic solvers for magnetic nanostructures

Simplified Neel-Arrhenius analysis is utilized to determine limiting densities versus SNR for longitudinal and keepered-perpendicular media. Dominant transition noise is assumed and the effects of grain size distribution and storage above room temperature are included. Perpendicular recording potentially exhibits a higher density than longitudinal; for example, at SNR=20 dB, the limiting densities are approximately 500 and 100 Gbit/in/sup 2/, respectively.

SNR and density limit estimates: a comparison of longitudinal and perpendicular recording

This paper presents a comprehensive critical overview of fundamental and practical aspects of the modern stripline broadband ferromagnetic resonance (BFMR) spectroscopy largely employed for the characterisation of magnetic low-dimensional systems, such as thin ferro- and ferromagnetic, multiferroic and half-metallic films, multi-layers and nanostructures. These planar materials form the platform of the nascent fields of magnonics and spintronics. Experimental and theoretical results of research on these materials are summarised, along with systematic description of various phenomena associated with the peculiarities of the stripline BFMR, such as the geometry of stripline transducers, the orientation of the static magnetic field, the presence of microwave eddy currents, and the impacts of non-magnetic layers, interfaces and surfaces in the samples. Results from 240 articles, textbooks and technical reports are presented and many practical examples are discussed in detail. This review will be of interest to both general physical audience and specialists conducting research on various aspects of magnetisation dynamics and nanomagnetism.

/pdf/broadband-stripline-ferromagnetic-resonance-spectroscopy-of-1at9ae3yp6.pdf

Broadband stripline ferromagnetic resonance spectroscopy of ferromagnetic films, multilayers and nanostructures

Corners and nucleation in Micromagnetics

The micromagnetic properties of a soft underlayer in perpendicular media are studied. It is shown that stray fields from a recording layer can substantially modify magnetic properties of soft underlayer material. The degree of modification is determined by the characteristic bit size in the recording layer and by the soft underlayer material magnetic characteristics. It is found that there exists a thin layer within a soft underlayer with reduced permeability. The effects of the presence of such a reduced permeability region within a soft underlayer on both reading and writing processes are discussed.

Micromagnetics of a soft underlayer

In single-pole heads with a pole tip cross section trimmed down to 1003200 nm by focused ion beam, the remanence of the head becomes nonzero if the pole length is too high. Large-scale three-dimensional micromagnetic simulations are performed to understand this effect, and to calculate the critical length of the pole as a function of the pole tip cross section.

Micromagnetic simulation of an ultrasmall single-pole perpendicular write head

Large scale 3D micromagnetic simulations are performed on single pole read heads with pole tip cross sections of 45345 and 1003200 nm. It is shown that tips with these dimensions have a much higher output than predicted by an analytical theory using the reciprocity theorem. The larger of these tips still behaves in a relatively soft manner and has an output waveform shape very close to the one predicted by the analytical model. The response of the small tip however is hysteretic.

Micromagnetic simulation of a flux guide for a read head with sub-100 nm resolution

We present our results on the development of magnetic sensors for application in magnetic probe recording. Successful writing experiments on a magnetic medium with perpendicular anisotropy show that magnetic domains of 130 nm can be reversed in a heat-assisted process. For reading purposes we propose a magnetoresistive sensor. The optimization of the shape of the sensor was performed using micromagnetic simulations with the requirement that the sensor has to be capable of both read and write operations. At this stage, the experimental realization of the sensor was carried out at a wafer-base level. The fabrication technique consists of a combination of optical lithography and focused ion beam etching.

K. Ramstöck

Papers

Corners and nucleation in Micromagnetics

Micromagnetics of a soft underlayer

Micromagnetic simulation of an ultrasmall single-pole perpendicular write head

Micromagnetic simulation of a flux guide for a read head with sub-100 nm resolution

A read and write element for magnetic probe recording