"Spicy world of NanoScience"
Microelectronics is in expectation of miracles. Discovery of the giant magnetoresistance phenomenon, thanks to which the HDD capacity has increased by a factor of a hundred at once, has inspired researchers for new exploits, specifically for search of an appropriate RAM replacement. If this task is solved, habitual equipment will change drastically, for example, a switched-on computer will start working from the “interrupted point” without waiting and loading. The future of microelectronics as it is considered by the world science, and the Russian researchers’ contribution to the progress is discussed in the interview with the vice-chancellor of Moscow State Technical University of Radio Engineering, Electronics and Automation Alexander Morozov.
Alexander Morozov: “It is great luck to find an area where you will be the first to get interesting and important results. I have been in the physical science for 36 years, and I came across only five or six zests like this throughout this period. Frustration is one of them.”
Alexander Igorevich, electronic industry is taking in scientific theories and developments very quickly, so researchers probably know better than all analysts what the industry future may hold. What changes are most likely and expected?
– This is indeed a thriving industry. If in the early 90s of the last century, the HDD capacity of our personal computers was about a hundred megabytes, by the mid-90s it increased by ten times, after which it grew quickly up to a hundred Gigabytes. Nowadays, the HDD capacity is coming closer to a Terabyte. This qualitative leap happened owing to giant magnetoresistance discovery made in 1988 by scientific groups under the guidance of a French physicist Albert Fert and a German physicist Peter Grunberg, who were awarded the Nobel Prize for this discovery in 2007 году. The industry immediately grasped the discovery, it seems to me, even quicker than physicists finally comprehended it. The companies that produce HDDs made new playback heads (which were more sensitive to the magnetic field) and smaller tracks on the disk. The outcome was as follows – much more information could be recorded on the same area of HDD, the HDD capacity has increased by a factor of a hundred at once. Naturally, this resulted in magnetoelectronics boom. New active research started, in the course of which other effects were found in the framework of this discovery. First of all – the possibility to create magnetic nonvolatile memory (NVRAM), which will probably come soon to replace current RAM. Nowadays, when the computer is switched on, everything is deleted from the RAM, and switching requires access again to a relatively slow hard disk drive, i.e. it is time-consuming. Should a new memory be in place, there will be no such inconveniences: after switching, the computer will start working from the place it stopped without any loading and waiting. In the future, such memory will replace the HDD and flash memory. A natural question arises: why this has not happened so far? The point is that this memory (MRAM or magnetoresistive memeory) is rather difficult to fit into an ordinary technological chain based on application of silicon semiconductors. Besides, it is very expensive, about a hundred times more expensive than the RAM is. Naturally, nobody would agree to its implementation in production quantities so far. Anyway, pathfinders have already appeared, specifically Motorola has already used it in its cell phones via making the MRAM-based memory chip. To make the technology popular, it should be got into shape, the cost should be decreased, and it should be adapted to existing technologies.
What is the contribution to the progress made theorists at Moscow State Technical University of Radio Engineering, Electronics and Automation, who are not bound either to experimentalists or to the industry?
– Yes, we are exclusively making theoretical study. As the above-mentioned technologies have not become widespread in Russia – neither HDDs or MRAM are produced in our country, as far as I know, indeed, we are not bound to anybody. We are studying magnetic nanostructures, where the giant magnetoresistance effect was discovered. Such elementary structure consists of two ferromagnetic metal layers separated by a layer of nonmagnetic or antiferromagnetic metal, and it is called a “spin valve”. It has turned out that roughness of interface between layers, the thickness of which being about one nanometer, cardinally influences their magnetic properties. Only theorists prefer to believe that boundaries are ideally smooth. But this is not the case in real life. Prior to our research commencement, it was known that presence at the interface of ferromagnetic and antiferromagnetic layers of atomic steps, changing the layer thickness by one atomic plane, led to appearance of frustration in the interlayer exchange interaction. At that, homogeneous distribution of magnetic parameters of order does not meet the minimum energy. Our research group pursued the following aim – to predict what distribution of magnetic parameters of order in the space will appear depending on the layer thickness and the distance between atomic step edges at the interface. The aim was successfully achieved for the case of two-layer ferromagnetic-antiferromagnetic nanostructures and spin-valve structures with an antiferromagnetic interlayer. We have been the first to solve this interesting basic task. Why is it needed from the practical point of view? Knowing phase diagram enables (via correct selection of technological parameters) to obtain the roughness of interface boundaries, which would ensure optimal characteristics of a given magnetoelectronic device. Of course, this requires enormous technologists’ work, however, without our theoretical calculations at hand, a technologist can carry out this search only by trial and error, i.e., by the hit-and-miss method.
How did the world scientific community apprehend your theories?
– The researchers working in this area acknowledge our priority. Specifically, we have predicted a new type of domain walls – frustration-caused domain walls. Their thickness has turned out to be significantly smaller than that of traditional domain walls, besides, it changed according to moving away off the interface boundary. Our work was published in 1998 at the domestic “Journal of Experimental and Theoretical Physics”. We persuaded experimentalists for a long time to verify our theory, but this required the nanometer resolution for magnetic properties investigation. Our colleagues had no such possibilities as a rule. At last, in 2004, the US journal Physical Review Letters published works by German researchers at the Max Planck Institute for Physics of Microstructures, Halle (Max-Planck-Institut fur Mikrostrukturphysik, Halle), where our predictions had been experimentally confirmed. The German researchers had not, in all probability, read our article, although the “Journal of Experimental and Theoretical Physics” is translated into English, therefore, they did not refer to our research right away, but only after we pointed to our publication.
A group of Italian researchers at the Polytechnic Institute of Milan experimentally discovered discretization of ferromagnetic layers in the “ferromagnetic–antiferromagnetic oxide–ferromagnet” nanostructures into nanodomains, as well as transition from a nanodomain state to a homogeneous state accompanied by the layer thickness change. They found only one theory that explained the observed phenomena – our theory, and they actively refer to us.
We can also be proud that we were invited to write chapters for two monographies published in the US and Germany, that were dedicated to giant magnetoresistance and antiferromagnetic oxide properties. It is interesting to note that we did not perform marketing, the publishers appealed to us by themselves and asked to tell about our activities, magnetic phase diagram, frustrations, etc. As a matter of fact, we have done everything we wanted on this subject, all findings have been published, so it is time to undertake something new.
Is it clear already what you are going to deal with?
– When selecting the research direction we shall make a start from our own knowledge, skills and interest towards the subject. Of course, it is great luck to find an area where you will be the first to get interesting and important results. It is well-known that a fruitful debut idea is great rarity. I have been in the physical science for 36 years, and I came across only five or six zests like this throughout this period. Frustration is one of them. No doubt that the largest “nuggets” have already been selected in this area. One can certainly continue to rock gravel for gold, but this is not that exciting. You will not get crucially new results already. As a person brought up in strict requirements, I believe that if experimentalists need some details, we certainly need to help them to sort out. However, it does not make sense to my mind to simply increase the number of parameters or to draw multidimensional phase diagrams.