Professor Oscar Céspedes

Oscar joined the condensed matter group in August 2009 with the objective of leading innovative, multidisciplinary research in organic spintronics. His research pursuits a multidisciplinary approach to nanotechnology, aiming to discover new paradigms arising from the combination of spin, molecular materials and quantum effects.

After graduating from the Physics department at the University of Zaragoza (Spain), Oscar became an intern at the National Laboratory of Intense Magnetic Fields (LNCMP) in Toulouse (France) as a research Erasmus scholar. During this time, he studied the electron-magnon (spin wave) interaction by doing simulations and measurements of the magnetoresistance of 3d transition metals at high magnetic fields (5-60 T), successfully determining the physical parameters for the magnons and their interaction with electrons.

He later joined the Physics Department at Trinity College Dublin to do a PhD under the supervision of Prof. JMD Coey. Initially he worked in the European project MAGNOISE, working on noise measurements in half metallic films and nanostructures. The excellence of research in spintronics at Trinity College was then recognised by two €5M grants by Science Foundation Ireland: CINSE and CRANN. Oscar was involved in both projects, contributing with the discovery of a magnetic proximity effect, or contact induced magnetism in carbon nanotubes (reported here in Physics World and one of the top papers in 2004 in J. Phys. Cond. Matt.) and performing the first measurement of electrically induced domain wall displacement in magnetic oxides using focused ion beam patterned Fe3O4 and LSMO nanoconstrictions.

After his doctoral work, Oscar took a position as European Young Researcher at the Atomic Energy Commission of France (CEA-Saclay) within the European network DYNAMICS. Working with Dr. Michel Viret, Oscar measured the experimental proof of magnetism in atomic platinum chains and fabricated a p-Si / NiOx diode with rectifying, tuneable magnetoresistance and photovoltaic properties. His second postdoctoral position was at the Department of Applied Quantum Physics at Kyushu University (Fukuoka, Japan). His research during his first year granted him a fellowship by the Japan Society for the Promotion of Science fellow for the following two years. In Japan, Oscar worked in the effects of RF magnetic fields on iron cage proteins and the optical properties of magnetite nanoparticles. The most remarkable result was the first proof of a non-thermal biological effect of RF magnetic fields, with protein function and molecular dynamics altered after exposure to fields of order 1 MHz and 15 mT (refs [1,2] and reported here and here by EMF-Portal).

Recently, his research on an emergent magnetism at molecular interfaces featured in Nature (link), with a News report in their front website (link) and a News & Views article in the same journal issue reporting the findings (link). This research was also widely reported by other sources, such as Cosmos Magazine, Physics World, Chemistry World, Science News and others.

He now oversees the magnetisation, organic film and Raman spectroscopy experiments, and currently supervises or co-supervises three PhD students and one postdoc working on organic magnetic tunnel junctions, topological insulators, and spin transport in carbon nanotubes. His research interests also include the electron/spin-phonon interaction, the correlation of molecular dynamics with electronic transport and Raman spectroscopy in extreme conditions.

Grants

Before coming to Leeds, Oscar participated in two European, two Irish and two Japanese research projects as researcher, co-investigator or principal investigator. The total budget of these grants was over £10 million, and he contributed to the experimental work, application, reporting and management of these projects.

Oscar is the PI for a running project in magnetometry funded by the Engineering and Physical Sciences Research Council (EPSRC) of the UK, with a total budget of £600 k including capital costs. The objectives include the study of the spin-phonon interaction, novel methods of operation for organic transistors, measurement of magnetic materials under extreme conditions and topological insulators. Previously, he was the PI for two projects dealing with spin spectroscopy and topological insulators. Oscar is also Co-I in a European Marie Curie training network.

Representative Publications:

1. L. Henrichs, O. Céspedes, J. Bennett, J. Landers, S. Salamon, C. Heuser, T. Hansen, T. Helbig, O. Gutfleisch, D. Lupascu, H. Wende, W. Kleeman and A.J. Bell, "Multiferroic clusters: a new perspective for relaxor-type room-temperature multiferroic", Advanced Functional Materials (in press).

2. F. Al Ma'Mari, T. Moorsom, G. Teobaldi, W. Deacon, T. Prokscha, H. Luetkens, S. Lee, G.E. Sterbinsky, D.A. Arena, D.A. MacLaren, M. Flokstra, M. Ali, M.C. Wheeler, G. Burnell, B.J. Hickey and O. Céspedes, "Beating the Stoner Criterion Using Molecular Interfaces", Nature 524, 69 (2015)

3. O. Céspedes, M. Wheeler, T. Moorsom and M. Viret, "Unexpected Magnetic Properties of Gas-Stabilized Platinum Nanostructures in the Tunneling Regime", Nano Letters 15, 45-50 (2015).

4. T. Moorsom, M. Wheeler, T.M. Khan, F. Al Ma'Mari, C. Kinane, S. Langridge, D. Ciudad, A. Bedoya-Pinto, L. Hueso, G. Teobaldi, V.K. Lazarov, D. Gilks, G. Burnell, B.J. Hickey and O. Céspedes, "Spin polarised electron transfer in ferromagnet/C₆₀ interfaces", Phys. Rev. B 90, 125311 (2014).

5. T. Moorsom, M. Wheeler, T.M. Khan, F. Al Ma'Mari, G. Burnell, B.J. Hickey, V. Lazarov, D. Gilks and O. Céspedes, "Effects of spin doping and spin injection in the luminescence and vibrational spectrum of C₆₀", Appl. Phys. Lett. 105, 022408 (2014).

7. O. Céspedes and S. Ueno, "Effects of Radio Frequency Magnetic Fields on Iron Release From Cage Proteins", Bioelectromagnetics 30, 336 (2009).

8. O. Céspedes and M. Viret, "Normal and Reversed Tuneable Magnetoresistance in a NiOx/p-Doped Silicon Diode", Appl. Phys. Lett. 94, 023504 (2009).

9. O. Céspedes, M. Viret and J.M.D. Coey, "Magnetoresistance in NiOx nanoconstrictions controlled by magnetic fields and currents", J. Appl. Phys. 103, 083901 (2008).

10. O. Céspedes, S. Watts, K. Dörr, M. Ziese and J.M.D. Coey, "Magnetoresistance and electrical hysteresis in stable half-metallic La0.7Sr0.3MnO3 and Fe3O4 nanoconstrictions", App. Phys. Lett. 87, 083102 (2005).

11. O. Céspedes, M.S. Ferrerira, S. Sanvito, M. Kociak and J.M.D. Coey, "Contact Induced Magnetism in Carbon Nanotubes", J. Phys.: Cond. Mat. 16, L155 (2004). Institute of Physics Select & Top Papers in J. Phys. Cond. Mat. 2004.

12. B. Raquet, M. Viret, E. Sondergard, O. Cespedes and R. Mamy, "Electron-Magnon Scattering and Magnetic Resistivity in 3d Ferromagnets", Phys. Rev. B 66, 024433 (July 002).