Marisa Medarde

Marisa grew up in Barcelona, where she completed her studies up to the master’s level. After working on the synchrotron and neutron sources in Paris and Grenoble for her PhD, she moved to Switzerland for a post-doc at the Paul Scherrer Institute (PSI). She was there for five years, having children during that time, before moving to spend two years at the Argonne National Laboratory in Chicago. The family then returned to Switzerland just as the children were starting school, and so Marisa decided to stay at home for four years. She was able to come back to science thanks to the Marie Heim-Vögtlin SNSF program meant to encourage women who have halted their careers for family reasons to come back to work. She received funding for three years and was able to work part time during this period, continuing on as a scientist at the “Research with Neutrons and Muons” division at PSI. She was appointed leader of the “Physical Properties of Materials” group in 2017.  

Interview by Carey Sargent, EPFL, NCCR MARVEL

The biggest challenge that woman scientists face is…

I think that there are two main challenges. One of them is that they have to work in an environment that has been designed for men by men. In the sciences, women are a minority—in the early stages it’s quite rare that there are more than 30% women and this only decreases as you go to higher levels. As a minority, certain things have been imposed on us and we have had to adapt to a male environment. This environment is very competitive and, to succeed, people need to be highly self-confident, ambitious, resistant to pressure and also to any uncertainty concerning future employment.

Then there are also the problems associated with combining professional and private lives. If you look at the statistics, most women scientists have partners who are also scientists, whereas the opposite is much less common. Women are thus much more often confronted with the “two-body problem”. Moreover, male scientists have often partners with less demanding careers and they can more easily follow. Then you have the biological clock—after 40 it can be complicated for a woman to start a family, whereas men can postpone this moment to when they are a little older. These two things go together to make it more difficult for a woman to have a scientific career.

In terms of how we can change this, I think that in the longer term it’s important to address how boys and girls are educated at school. More immediately, I think the first thing is to recognize that there is a problem—for some people it is not so obvious—and then take action to mitigate it and to compensate somehow. Women have to face disadvantages that men usually don’t, but they can be excellent scientists. My own experience with female scientists –past and present- has been very good, and I’m happy to see that their number increases in the new generations.

I chose a scientific career because…

It was a high school physics teacher who managed to excite my curiosity. I was also lucky that my parents supported me -I was the first one in my family to take this path.  

If I were not a scientist, I would be…

I have loved history ever since high school. So I think I could have been a historian. I find this fascinating, and it also helps us understand today’s challenges. Who knows, maybe it’s something I will pursue when I will retire, as a hobby.  

My most exciting MARVEL discovery to date has been…

We have obtained very nice results and benefited from great collaborations with MARVEL theoreticians in two different areas, but I’m particularly proud of one of them, namely, the experimental demonstration that chemical disorder can be used to fine-tune magnetic frustration and stabilize magnetic spirals at very high temperature.     

The materials we were investigating are multiferroic oxides with a layered perovskite structure. The term multiferroic designates materials with more than one ferroic order (ferromagnetism, ferroelectricity, ferroelasticity and ferrotoroicity), although today it usually refers to the combination of magnetic and ferroelectric orders.  An interesting aspect of combining magnetism and ferroelectricity in the same materials is that they can be coupled. This means you can change one of them by manipulating the other one. This property can be exploited in a number of technological applications. However, this requires that the coupling exists at room temperature, and preferably above.

Among the materials which display magnetoelectric coupling, spiral magnets have attracted a lot of attention since it was experimentally and theoretically demonstrated that such non-centrosymmetric spin arrangements can induce ferroelectricy. The problem is that magnetic spirals are usually the result of the competition between next and next-nearest magnetic exchange interactions, a fact that, with a few exceptions, leads to very low spiral order temperatures (typically below -200°C).

In the layered perovskites that are the object of our investigations, we could experimentally demonstrate that magnetic spirals can be stabilized at room temperature (up to 30°C).  The most intriguing fact was that we could achieve this through the manipulation of chemical disorder, which is usually detrimental for magnetic order. These results motivated Nicola Spaldin and her MARVEL post-doc Andrea Scaramuci, who immediately realized that current theories were not enough.  Hence, they developed a very innovative, disorder-based model that could explain why, for this particular family of materials, magnetic spirals can be stable up to very high temperatures. They also made a few predictions, some of which could be experimentally verified by my group. This continuous interaction between theory and experiment led to a further increase the spiral order temperature, that we could push up to 100°C. This value is comfortably far from room temperature, an important point regarding the possible use of these materials in real-life applications.

A point I would like to highlight is that this discovery benefited from the excellent experimental facilities at the Paul Scherrer Institute, and in particular at the Laboratory for Neutron Scattering.  The input of other theory teams at MARVEL, the Paul Scherrer Institute and the University of Groningen was also very important, making from this project a great example of a successful collaboration between theory and experiment. We published four papers (three of them in high-impact journals), a theory paper is submitted, and I’m convinced there is still the potential to produce high-level results.  

My top two papers are...

As the first one, I would choose one of the four papers mentioned in my previous answer. All made important contributions, but one of them was truly pioneering because it provided the experimental proof that a completely unexpected tool  — chemical disorder —   can be used to tune order temperature of a magnetic spiral over unprecedentedly large temperature ranges .  

M. Morin, E. Canévet, A. Raynaud, M. Bartkowiak, D. Sheptyakov, V. Ban, M. Kenzelmann, E. Pomjakushina, K. Conder and M. Medarde, "Tuning magnetic spirals beyond room temperature with chemical disorder", Nature Communications 7:13758 (2016).

The other paper is older, a review article I wrote in 1997, when I was a postdoc at the Paul Scherrer Institute. It was on Ni perovskites, which displayed metal to insulator transitions, a topic I was working on during my PhD. Thanks to MARVEL, I came back recently to this subject in collaboration with the theory teams of Claude Ederer, Nicola Spaldin and Antoine Georges.  When I was a post-doc, very few people were interested in these materials. The reason was that their study presents a certain number of difficulties for both theorists and experimentalists. There are theories that can explain how a metal works and also theories that can explain how an insulator works, but here we have something that is at the boundary between metals and insulators, and theories often don’t work very well.  Moreover, they are very difficult to prepare - the synthesis requires the use of very high oxygen pressures, so, for a long time, very few people had access to the samples. Since 10-15 years some of these materials can be prepared as thin films.  This has increased the amount of available experimental data, and the progress in characterization and modeling tools has boosted the interest of the solid state physics community. As a result, nickel perovskites are now considered to be challenging, but at the same time they are very clean materials for the experimental verification of theories dealing with correlated electrons and their evolution from localized to itinerant behavior.  Interestingly, little experimental progress has been made in bulk materials during the last 10-15 years. This is why the review, which deals exclusively on bulk nickelates, remains a reference more than 20 years after its publication.

M. L. Medarde, "Structural, magnetic and electronic properties of RNiO3 perovskites (R = rare earth)", Review article, Journal of Physics: Condensed Matter 9, 1679 (1997).