The Nobel Prize in Physics 2007
Albert Fert, Peter Grünberg
I was born in March 1938 in the small town of Carcassonne in the south of France. Later, and until I was two years old, I lived in Toulouse, another city in Southern France, where my parents were high school teachers, my father in physics and my mother in economics. But war loomed on the horizon. My father was mobilized into the army in June 1939, two months before the birth of my brother André. In 1940, he was captured and made a prisoner of war by the Germans; he returned home only in 1945. For the duration of the war, my brother and I were sent to live at our grandparents' farm in Montclar, a very small village in the foothills of the Pyrénées. My mother, who continued to teach in Toulouse, came to see us every weekend and so, until the age of seven, I lived the life of a country boy, milking the goats, harvesting grapes in my grand father's vineyards, setting snares for rabbits or hares. I lived very close to the world of plants and animals and very far removed from the world of physics.
In June 1945, my father returned from prisoner of war camp and our family was reunited in Toulouse. I became a city boy with a longing for life in the countryside. My father, while continuing to teach high school, prepared his doctoral thesis. Eventually, he was promoted to the rank of Professor at the University of Toulouse where he made important contributions to the development of electron microscopy. My brother and I applied ourselves studiously to our primary and secondary school work. Our father followed our progress in the sciences. Unquestionably, his penchant for rigorous thinking had a major influence on my approach to mathematics and physics. I earned good grades in the sciences. During my adolescent years, I also developed a great interest in literature, the arts and sports. At the age of fourteen, I began playing rugby and I was very proud of being selected to play in our high school team. At the age of seventeen, having completed my studies for the baccalauréat, I found myself drawn to Paris and above all to the Ecole Normale Supérieure (ENS), not only because it was a prestigious institution but also because it had the added attraction of being in the center of Paris, close to the Latin Quarter and St. Germain des Près, and at the heart of the city's intellectual life. I worked hard to prepare for the competitive entrance examinations at the ENS, in mathematics and physics. I was accepted. In September 1957, I lightheartedly left Toulouse for Paris and the Ecole Normale Supérieure.
My six years at the Ecole Normale Supérieure between the ages of 19 and 24 were a very intense period of my youth. The richness of my life on the small campus of the rue d'Ulm came from daily contacts with students working in a broad spectrum of disciplines, the sciences, philosophy, literature, history etc. In addition Paris was everywhere around us, with its museums, exhibitions, cinemas, concert halls and jazz clubs. I became a passionate fan of jazz, photography, film. I actually wrote a script and made a film.
It is possible that I might have been diverted from the pursuit of a career in science had I not been studying with excellent physics instructors. In particular, Jacques Friedel, who had established a physics program at the masters degree level, exposed me to the most up to date developments in condensed matter physics and emphasized as well an in depth teaching of quantum mechanics and statistical mechanics. It was this program which drew me into the study of condensed matter physics. When I returned from my military service in 1965, I began work on my doctoral thesis under the direction of Ian Campbell, in the Laboratory for Solid States Physics at Orsay which Jacques Friedel directed. I had the good luck of having the thesis topic: "Testing the suggestion of Neville Mott (future Noble Prize laureate) that the mobility of electrons in a ferromagnetic metal depends on the orientation of their spin in relation to their magnetic orientation". In the course of the research for my thesis, I became hooked on physics. I discovered that the work of a young inexperienced researcher can open many doors – provided that his experiments are well executed and rigorously interpreted. My findings in my thesis, as well as my in-depth knowledge of the physics of electron transport, made it possible for me to return to this subject fifteen years later and to discover the giant magnetoresistance. I am still surprised when I see that my findings during that earlier period comprise a large part of the basis for spintronics today.
However, when I defended my thesis in 1970, the available technologies did not allow for further advancement in the direction of giant magnetoresistance and spintronics. Although a concept similar to that of GMR already had emerged from my thesis experiments on ternary alloys, it proved impossible to extend it to the case of multilayers because it was impossible at that time to produce sufficiently thin layers. Thus, the exploitation of the influence of the spin on the mobility of electrons in ferromagnetic metals had to be postponed until the mid 1980s. Following a post-doctoral appointment at the University of Leeds, I returned to Orsay to take up a position as Assistant Professor at the University of Paris-Sud and to supervise a small group of doctoral students and post-docs at the Laboratory of Solid State Physics. I was promoted to the rank of professor in 1976. Marie-Josée and I lived in Paris; Ariane and Bruno, born in 1968 and 1971, were growing up and I divided my time between family life and a very sustained effort in research and teaching. During our summer vacations, we returned to the Mediterranean and the Pyrénées, to the home of my parents in Banyuls sur Mer, close to the Spanish frontier. My research activities during the 1970s and at the beginning of the 1980s touched on a variety of subjets and yielded fruitful results. The thesis of my first doctoral student, Alain Friederich, shed new light on problems relating to the Hall effect and to the anisotropy of magnetoresistance linked to spin-orbit coupling. Today the Spin Hall effect has become a hot topic in physics. I think that some of our results from that period should have an impact on spintronics today. In 1975, in order to interpret our results on the Hall effect and the anisotropy of interactions between electrons and magnetic impurities, I began a collaboration with Peter M. Levy, a theorist at New York University. Over the course of several years, I spent many summer months at New York University and learned to love the city, Greenwich Village and its jazz clubs, SoHo and its art galleries. My collaboration with Peter Levy on theoretical problems encompassed numerous subjects and, among other results, led to the discovery of the existence of Dzyaloshinsky-Moriya interactions in spin glasses. One consequence of these interactions is the triad anisotropy in spin glasses, which was confirmed experimentally in the thesis of my Ph.D. student Dimitri Arvanitis.
In the mid 1980s, it seemed likely that techniques developed in the field of microelectronics would make it possible to grow magnetic multilayers built up from layers of nanometer thickness. It was precisely at this time that my former student, Alain Friederich, was developing Molecular Beam Epitaxy (MBE) in his research group of the Thomson-CSF company. While attending a meeting in San Diego in 1985, Alain Friederich and I were discussing our work at a bar next to the swimming pool, under the palm trees and the stars and we decided to collaborate on the growth and study of magnetic multi-layers. With help from the expert on MBE at Thomson-CSF, Patrick Etienne, as well from my doctoral students, Frédéric Nguyen Van Dau, Frédéric Petroff and Agnès Barthélémy, and two post-docs, Mario Baibich and Jean-Marc Broto, our collaboration resulted in the discovery of giant magnetoresistance at the beginning of 1988.
On the day we discovered giant magnetoresistance, we were measuring several multilayers of Fe/Cr, one after the other. We were not altogether certain about the quality of the multilayers that contained the thinnest layers of chromium. Exercising caution, we began by measuring multilayers in which the layers of chromium were the thickest. We determined that there was indeed a magnetoresistive effect. We then moved on to multilayers in which the chromium layers were progressively less thick. And wonder of wonders! The greater the decrease in the thickness of the chromium, the larger the magnetoresistance. The final measurement, which we took on 0.9 nm of chromium, was stupefying. The resistance increase between the parallel and anti-parallel configurations of the layers of iron went up to 80%! We had just participated in the birth of the phenomenon which we called giant magnetoresistance (GMR).
The International Conference on Magnetism which took place in Paris at the beginning of July 1988 offered us our first occasion to present the results of our work on giant magnetoresistance in Fe/Cr multilayers. However, my Ph.D. student Frédéric Nguyen Van Dau had only a few minutes in which to make his presentation and therefore his paper did not provoke much of a response. Peter Grünberg did not attend the conference. It was only the following week, at the International Conference on Magnetic Films and Surfaces (ICMFS) at Le Creusot in Burgundy, that Peter Grünberg and I were able to present the details of our respective results and to take the measure of the considerable interest which our findings provoked among members of the magnetism community. At this conference, I also was able to explain my earlier results which showed the influence of spin on the mobility of electrons in ferromagnetic metals and to present the interpretation of "GMR" on this basis. Interest within the magnetism community in this new type of phenomenon which exploited the spin of electrons in magnetic nanostructures grew exponentially following the publication of our article by Physical Review Letters in December 1988. I have some heartwarming memories of this period. As I neared the end of my first paper on this subject presented at a conference in the United States, I was anxious to know whether I would be able to complete my presentation within the designated time frame. I asked Bret Heinrich, the Chair, what time was left. He told me that, given the level of interest in the work I was presenting, I could continue for as long as I wanted. Every researcher dreams of such a response from the chair. Thanks Bret!
Beginning in l989, the physics of multilayers and GMR became very hot topics and subjects of research in an increasing number of laboratories. In addition, my own research activity was expanding on many fronts. Apart from experimental work on the Fe/Cr systems in the theses of Frédéric Nguyen Van Dau, Agnès Barthélémy and Frédéric Petroff, I developed, with Agnès Barthélémy, a semi-classical theory of GMR which complemented that of Camley and Barnas. I also collaborated with Peter Levy and Shufeng Zhang of New York University on the development of the first quantum model of GMR. In 1990, we began to study multilayers prepared by sputtering in a collaboration with the team of Peter Shroeder, Jack Bass and Bill Pratt at Michigan State University (MSU). This collaboration led in 1991 to the first observation of GMR and of oscillations in the interlayer coupling for the Co/Cu system by my doctoral student Dante Mosca. Stuart Parkin obtained similar results at approximately the same time in Almaden. The system Co/Cu later became the archetypical GMR system. The first observations of inverse GMR in the thesis of Jean-Marie George constitute another important result of my team in the early 1990s. Beginning in 1991, I became interested as well in results of the team at MSU on GMR in the geometry where the current is perpendicular to the plane of the layers (CPP-GMR). In collaboration with a young researcher at Thomson-CSF, Thierry Valet, I developed a theory of the CPP-GMR based on the concept of spin accumulation. Today, this theory has become essential for many current developments in spintronics. The 1993 Valet-Fert paper in Physical Review is my second most frequently cited paper, coming just after the paper in which we presented the discovery of GMR. Beginning in 1994, I collaborated with Luc Piraux at the University of Louvain, on studies of CPP-GMR using multilayered nanowires. These studies made it possible to extend the results of MSU to much greater thicknesses and to confirm the length scale linked to the effects of spin accumulation in the Valet-Fert model.
Thus, the beginning of the 1990s was for me and my research team a period of intense and fruitful activity during which we made important contributions to the development of the physics of GMR and to the establishment of essential concepts in spintronics. Peter Grünberg and I, in collaboration with firms like Thomson-CSF, Philips and Siemens, have participated as well in several projects financed by the European Community in order to further the development of new applications. The year 1994 brought us international recognition, with the 'International Union of Pure and Applied Physics' presentation of its Magnetism Award to Peter Grünberg and myself, and the American Physical Society's award of the International Prize for New Materials to Peter Grünberg, Stuart Parkin and me. It also strucks me at this time that GMR was only a first step in the exploitation of spin in magnetic nanostructures and that this first step had opened the door to a much larger field of research - the field we now call spintronics. Alain Friederich, the director of the physics group at the laboratories of Thomson-CSF, proposed to me that we create a new laboratory which would bring together the CNRS and Thomson-CSF for a joint exploration of the perspectives opened up by GMR. We proposed a research program which moved us into a large number of new areas: magnetic tunnel junctions, half-metallic ferromagnets, spin injection phenomena, spin transport in semi-conductors ... The project was accepted. The new laboratory, called the Unité Mixte de Physique (UMP) CNRS-Thomson-CSF, (which later became the UMP CNRS-Thales) was established in the spring of 1995, at Corbeville, a few kilometers from the University of Paris-Sud. An agreement joined the laboratory to the University, in which I continued my teaching. From the beginning, the laboratory brought together my team at Orsay, the team of Thomson-CSF with which we were collaborating and several researchers and engineers at CNRS: Jean-Marie George, Annie Vaurès, Jean-Luc Maurice (shortly thereafter, a team for the study of superconductivity joined the laboratory). Since then, it is within this Unité Mixte CNRS-Thales that my research activity has progressed in many directions in the field of spintronics. The team has been progressively enlarged with the arrival of new researchers from CNRS and assistant professors from the University of Paris-Sud - Abdelmadjid Anane, Manuel Bibes, Vincent Cros, Cyrile Deranlot, Julie Grollier, Henri Jaffrès, Richard Mattana and Pierre Seneor.
It is difficult for me to describe my research activities at the CNRS/Thales laboratory between 1995 and 2007 precisely because this activity has moved in so many directions and has explored very diverse dimensions of spintronics. I can only refer the reader to my Nobel Lecture for details about the results of this activity. It is also the case that the relatively young members of my team are achieved their independence and have progressively developed their own research programs. Numerous and diversified studies of magnetic tunnel junctions have been undertaken by Frederic Petroff, Agnès Barthélémy and Vincent Cros. Agnès Barthélémy, assisted by Manuel Bibes, is now responsible for all research on the applications of magnetic oxides and multiferroics in spintronics. Our very important activity on the phenomena of spin transfer is being developed, for the most part, by Vincent Cros and Julie Grollier, with the help of Abdelmadjid Anane and Henri Jaffres. Spintronics involving semiconductors is being studied by Jean-Marie George, Henri Jaffres, Abdelmadjid Anane and Richard Mattana. Single electron spintronics has become the domain of Pierre Seneor and Frédéric Petroff, while Frédéric Nguyen Van Dau directs the development of various applications and Jean-Luc Maurice is the expert in structural studies. An activity in molecular spintronics is in the process of being launched by Pierre Seneor, Frédéric Petroff, Jean-Marie George and Richard Mattana. All of them are currently participating in the development of nanotechnologies, with the valuable assistance from Cyrile Deranlot and from Karim Bouzehouane, Stéphane Fusil and Eric Jacquet of the superconductivity team. As for me, I am making every effort to participate in most of these current activities. I also have been able to devote myself a little more to theory: the modeling of single-electron spintronics with Jozef Barnas at the University of Poznan; the theory of the injection of spin into semiconductors with Henri Jaffrès; the theory of the phenomenons of spin transfer with Peter Levy, Henri Jaffrès, Jozef Barnas.
The year 2007 marked a high point in the activity of the UMP CNRS/Thales. It was rich in new results and publications and, for me, abundant in scientific prizes: the Japan Prize in April, in Tokyo; the Wolf Prize in Physics in May, in Jerusalem and the Nobel Prize in December, in Stockholm. The Nobel Prize, of course, has changed my life. I have received innumerable requests; and new responsibilities are on the horizon. In addition, I am eager to return to my research projects and to concretize my recent ideas. A difficult challenge! I also hope that the Nobel Prize will facilitate the entire team's energetic communication of its ideas and messages.
In conclusion, I want to thank all those who have helped me to become who I am today: first of all my parents and Marie-Josée; also Jacques Friedel and Ian Campbell, my first guides in my trajectory as a physicist; Alain Friederich, with whom I was able to launch a collaboration which was decisive for the discovery of GMR; the team at the Unité Mixte CNRS/Thales, and, finally, all those who have worked with me during my forty year-long career as a physicist.
From Les Prix Nobel. The Nobel Prizes 2007, Editor Karl Grandin, [Nobel Foundation], Stockholm, 2008
This autobiography/biography was written at the time of the award and later published in the book series Les Prix Nobel/Nobel Lectures. The information is sometimes updated with an addendum submitted by the Laureate.Copyright © The Nobel Foundation 2007