Hello, I am Rolando Valdés Aguilar and I am a graduate student in the Department of Physics at the University of Maryland where I am a member of the Magneto Optics group with Prof. Dennis Drew.

My research activities are focused on understanding the optical properties of multiferroics. These systems have become attractive since they present coupling between the magnetic and ferroelectric degrees of freedom. From the fundamental physics point of view, these systems allow us to study the coexistence and competition between different types of order.

This work is done in collaboration with postdoctoral research associate Andrei Sushkov and my advisor Professor H. Dennis Drew, we receive single crystals from Prof. S-W. Cheong from Rutgers University. We have recently reported the existence of electric dipole active magnetic excitations, so called electromagnons, in TbMn₂O₅ and YMn₂O₅, see publications.

We have also studied the system Eu_0.75Y_0.25MnO₃ which is very similar to TbMnO₃. We have discovered a colossal coupling of the IR active phonons to the magnons in this material. We have clarified the spectral structure of the electromagnons in this class of materials, and also have unequivocally shown that these excitations have nothing to do with f-level transitions. We point out as well that the selection rule for the multiferroics RMnO₃ is unique, e||a always independent of the ferroelectric state. Look at some of these results on this poster that I presented in the Strongly Correlated Electron Systems Conference in Houston, TX in May 2007.

I have also been recently involved in studying frustrated magnetic systems. I have prepared a manuscript of the study of spin-phonon coupling in the geometrically frustrated magnet CdCr₂O₄. The results are very similar to the ones obtained in ZnCr₂O₄ and are presented in this poster that was presented in the APS March Meeting 2007 (see also Publications below). This work is done in collaboration with Prof. Oleg Tchernyshyov and his graduate student Gia-Wei Chern from Johns Hopkins University.

We have recently carried out measurements on the magnetic field dependence of the electromagnons in both families of multiferroics RMnO₃ and RMn₂O₅. Their behaviors are markedly different. We are now working with Prof. Maxim Mostovoy of the University of Groningen in The Netherlands to develop models that explain these behaviors. We are writring manuscripts to that effect.

Finally, I am also starting to prepare my Ph.D. thesis dissertation. It will be centered in the optical properties in the far infrared and their magnetic field dependence. I will divide this work into the studies of geometrically frustrated systems and interaction frustrated systems. It seems that the latter are more suitable for multiferroicity to appear.

publications

• Origin of electromagnons in RMnO₃ (In preparation).
• Electromagnons in multiferroic RMn₂O₅ compounds and their microscopic origin (Journal of Physics C. Special Issue on Multiferroics (To be published)).
• Spin-phonon coupling in frustrated magnet CdCr₂O₄ ( PRB 77 092412).
• Colossal magnon-phonon coupling in multiferroic Eu_0.75Y_0.25MnO₃ (PRB 76 060404 ).
• Electromagnons in multiferroic YMn₂O₅ and TbMn₂O₅ (PRL 98 027202 (2007)).
• Infrared phonon signatures of multiferroicity in TbMn₂O₅ (PRB 74 184404 (2006)).