Nano Data Storage: Characterisation of nanomagnets for ultra-high density storage applications

Introduction
Novel nanomagnetic materials are being investigated for a wide variety of applications, in particular in future data storage devices. The growth in the storage capacity of the ubiquitous hard disk drive (HDD) has been extraordinary and has been achieved by the miniaturisation of components (the read/write head geometry, media thickness, grain diameter) and the development of novel recording media. However, problems with thermal instabilities will limit the storage density to ≈1Tb/in2 using current approaches, so a paradigm shift is required to enable continued growth. The use of bit-patterned media (BPM) is seen as one solution to this problem, whereby a single bit is stored on a single magnetically isolated nano-sized magnetic island. The exciting challenge in developing BPM lies in the fabrication of island arrays, with uniform island properties, at dimensions close to the limits of today’s lithographic approaches (1Tbit/in2 requires islands to be spaced on a 25nm x 25nm lattice). It is therefore vital that the magnetic properties of fabricated nanostructures are fully understood, since studies have shown that the reduction of island dimensions leads to an undesirable variation in the magnetic field required to switch individual islands.

Project
The challenging aim of this project is to characterise the magnetic behaviour of fabricated structures using the anomalous Hall effect (AHE). The AHE is a very sensitive technique that makes it possible to distinguish the switching of individual magnetic nanostructures as an external field is applied. In order to use the AHE a Hall cross structure must be etched into the sample to act as a current guide and allow the characteristic Hall voltage to be measured. This project will involve the fabrication of such structures to enable the switching behaviour of magnetic nanostructures to be investigated so that we can develop new media with controlled characteristics for future HDDs. The fabrication skills developed are applicable to all areas of nanofabrication.

The NEST Group
The Nano Engineering & Storage Technology (NEST) group is housed in an integrated suite of staff offices, general-purpose laboratory space and class 100/1000 cleanrooms. The group is a founder member of the Manchester Centre for Mesoscience and Nanotechnology (CMN), which is based in the group’s laboratories and contains state of the art lithography tools for the fabrication and visualisation of nanoscale structures. The group also has facilities for characterising magnetic media including a purpose built alternating gradient field magnetometer and an ADE Technologies vector vibrating sample magnetometer.