Harnessing magnets to improve the capacity of data storage devices

Even as a school boy in Madurai, magnets and their magical properties to attract and repel fascinated Vignesh Radhakrishnan. And so when he set out to do a PhD many years later, it came as no surprise that he chose 'New Generation Molecular Magnetic Materials: Experiment and Theory'.

Graduate research scholars at the IITB-Monash Research Academy like Vignesh study for a dually-badged PhD from both IIT Bombay and Monash University, Australia, spending time at both institutions to enrich their research experience. IITB-Monash Research Academy is a collaboration between India and Australia that endeavours to strengthen scientific relationships between the two countries.

Picture Credit: Avaragado, by Fliker

Researchers have for long been trying to unravel the mysteries of Single Molecule Magnets (SMMs), which represent the smallest possible magnetic devices and are a controllable, bottom-up approach to nanoscale magnetism. SMMs have been proposed as potential candidates for several technological applications that require highly controlled thin films and patterns. One possible use of SMMs is superior magnetic thin films to coat hard disks.

A single molecule magnet is an example of a macroscopic quantum system. If spin flips could be detected in a single atom or molecule, the spin could be used to store information. This would lead to an increase in the storage capacity of computer hard disks. Several other exciting potential applications have been envisaged such as quantum computing, magnetic refrigeration and "Spintronic" devices.

So what makes SMMs capable of a high level of information storage?

Vignesh enthusiastically explains, "A molecule which exhibits slow relaxation of magnetisation even in the absence of a magnetic field is commonly called an SMM. The ability of these SMMs to retain spin orientation at certain temperatures [known as the blocking temperature (TB)] may lead to information storage at nano-level. Requirements for a molecule to exhibit SMM behaviour include a high spin ground state (S), with negative zero field Splitting (ZFS) parameter, D. Other desirable properties include negligible intermolecular magnetic interactions, large pair-wise magnetic exchange and a low probability for quantum tunnelling of the magnetisation (QTM). The combination of S and D results in an energy (anisotropy) barrier (U) to the reversal of the magnetisation vector, which depends directly on the square of the spin, and on its magnetic anisotropy (DS2). This leads to a case, where, upon application and removal of a magnetic field the system can be stabilised in one of the high-spin energy wells."

Picture Credit: Vignesh

"Earlier," he continues, "the search for SMMs was based primarily on 3d transition metal ions such as Mn(III). Recently, however, the design and synthesis of heterometallic 3d-4f clusters have received great attention since the discovery that such complexes are potential SMMs. Lanthanide (Ln) metal ions bring a large ground-state spin and, in some cases, a strong easy axis anisotropic magnetic moment. Therefore, the incorporation of Ln ions into such molecules has been recognised as an appealing route to new SMMs."

Under the close supervision of Prof. G. Rajaraman and Em. Prof. Keith S. Murray, Vignesh has so far conducted Density Functional Theory (DFT) calculations on four manganese heptanuclear disc-like [Mn7] complexes and three iron [Fe] di-nuclear complexes. He has synthesized seven Mn8Ln8 (Ln= Dy,Ho,Er,Yb and Y) wheel type and ten Mn3Ln2 (Ln= Gd, Tb, Sm, Eu and Dy) pentanuclear complexes, and discovered, to his delight, that some of them are exhibiting SMM behaviour.

"One of the distinguishing features of the IITB-Monash Research Academy PhD programme is the strong industry focus and application orientation of the topics researched by the scholars. Vignesh's work on molecular magnets addresses a key need in many electronics applications, that of increasing information storage capacity. Studies such as this attempt to bridge the gap between cutting edge research and the needs of the electronics industry, an important challenge for India today," says Professor Murali Sastry, CEO, IITB-Monash Research Academy.

Vignesh too is excited about the potential industrial applications of his research. "Nowadays people are using data storage devices like hard disks and USB drives, which offer storage capacity in terabytes (TB). If harnessed optimally, SMMs will increase the capacity much beyond terabytes. This will be a significant contribution to take technology to the next frontier."

Vignesh's teachers in Madurai will be watching closely. And so will we

Research scholar: Vignesh Radhakrishnan, IITB-Monash Research Academy

Project title: New Generation Molecular Magnetic Materials: Experiment and Theory

Supervisors: Prof. G. Rajaraman and Em. Prof. Keith S. Murray

Contact details: vignesh.kuduva@monash.edu

Contact research@iitbmonash.org for more information on this, and other projects.

The above story was written by Mr Krishna Warrier based on inputs from the research student and IITB-Monash Research Academy. Copyright IITB-Monash Research Academy.