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Ehtsham Ul Haq (promotion date: 15 September 2005)

Nanoscale spin-dependent transport of electrons and holes in Si-ferromagnet structures.

Promotion Date: 15 September 2005

Tomczak

Besides an electrical charge, electrons also have a spin. This spin is in two directions, called spin up and spin down. Up to the eighties semiconductor devices were only using the charge property of electrons. Continuous reduction in the size of semiconductor devices allowed to design electronic circuits with improved functionalities. However, it is obvious that soon we will reach fundamental limit regarding how small and reliable electronic devices can be made. Therefore, there is a need to search for new approaches, which can improve the performance of electronic devices. One of such approaches is “spintronics”, a technology that aims to utilize spin of an electron in addition to its charge.

What was your thesis about?

Besides an electrical charge, electrons also have a spin. This spin is in two directions, called spin up and spin down. Up to the eighties semiconductor devices were only using the charge property of electrons. Continuous reduction in the size of semiconductor devices allowed to design electronic circuits with improved functionalities. However, it is obvious that soon we will reach fundamental limit regarding how small and reliable electronic devices can be made. Therefore, there is a need to search for new approaches, which can improve the performance of electronic devices. One of such approaches is “spintronics”, a technology that aims to utilize spin of an electron in addition to its charge.

It is considered that spintronics is born with the discovery of Giant magnetoresistance (GMR) effect which is observed in multilayer structures consisting of alternating thin films of ferromagnetic and non magnetic metals. The resistance of the structures depends on the relative orientation of magnetization of ferromagnetic layers. The potential of this new discovery was soon realized, and today GMR sensors hold a bulk of the market share in

commercial hard disk drives. In 1997 another important class of spintronics devices emerged when large values of tunnelling magnetoresistance was discovered in magnetic tunnel junctions (MTJs). MTJs form the basis of non-volatile magnetic random access memory (MRAM). Today, there are quite a few spintronics devices e.g. spin valve transistor and magnetic tunnel transistor which have actively been developed. The further improvement of these devices so that they can be used commercially, requires a better understanding of the correlation between structural, transport, and magnetic properties of these devices.

What did you find?

We developed a new technique, which can study local spin-dependent transport of hot electrons; surface an interface microstructure, and magnetic domain structure simultaneously. We found that the technique has magnetic resolution better than 20 nm. If spintronics is to emerge as a new technology then it is vital that it gives new functionality to present electronic devices while keeping the main features of the present technology. One of the important features of conventional electronics is the complementariness, which allows designing electronic circuits with much lower power consumptions. Keeping this in view we explored for the first time spin-dependent transport of hot holes. In order to study spin-dependent transport of hot holes we developed a new technique called ballistic hole magnetic microscopy. Surprisingly, we found that a large spin filtering of hot holes also exists in the same system where spin-filtering of hot electron has been observed. The techniques can also be used to study magnetic switching properties at nanoscale. We found that the switching properties are different at different locations of the structure. Furthermore, they do not reproduce in successive magnetic field cycles.

Has your research generated a lot of interest, from commercial parties for instance?

If you talk about scientific interest, then yes. Our results were very well received by the scientific community during various conferences. However, the development for example of complimentary spintronics will require much more joint efforts from various research groups.

But since it is such a high risk subject with regard to results, how did it work out for you?

I had one whole year of wandering around, but in principle I was lucky. I had a lot of support from my supervisors and have good technicians in the group. But there were whole nights I had to spend in the lab to get what I wanted. Only after two years we got our first promising results.

Did that not worry you?

Yes. But I got plenty of encouragement of Professor Cock Lodder and Ronny Jansen who assured me that the results would come. And they did.

How did you come to do your PhD here?

I won a prestigious scholarship in Pakistan to do a PhD abroad. However, there was not enough funding and I went to Sweden to do,another Master’s in Material Engineering. After that I wanted to do a PhD there, but there were also some problems with the funding. Then I applied and got a position in this group.

Did you enjoy it here?

Yes, I enjoyed the work and the opportunity to work on such a challenging device.

And I enjoyed my house here in Enschede. My wife and I really took the trouble to make it beautiful, it was the first house we had to ourselves after our marriage. It gave us great pleasure living there. And we had our two children here.

And what didn’t you like?

I don’t know. I don’t think about the negative side. Had I stayed in Pakistan there would have been disadvantages as well. Everywhere you go you will find good things and bad things and it is better to have an eye for the good things.

What are you going to do next?

I already have a post doc job in Sheffield University in Britain, building instruments for nanotechnology.