Horacio A. Farach, Professor

Electron spin resonance studies of mixed crystals and glasses containing transition metal ions; ferroelectric and antiferomagnetic phase transitions. Monte Carlo and effective field calculations in magnetic systems. Low field absorption in high temperature super conductors. Among the most active areas of research in condensed matter physics are critical phenomena, domain growth far from equilibrium, and high temperature superconductors. These problems are addressed in our experimental program on the magnetic properties of superconductors and their relationship to Josephson junctions and equilibrium and dynamical properties of ferroelectrics. Using novel electron paramagnetic resonance (EPR) techniques developed by our group, the microscopic details of the polarization in KDP (potassium dihydrogen phosphate) type ferroelectrics are studied. In particular, the EPR method provides information about the rate of nucleation on the growth of ferroelectric domains and on the dynamics of electric field switching. Using a homemade EPR spectrometer we are studying microwave absorption at zero and low magnetic field of high temperature superconductors. The processes of fluxon entry, motion, and pinning are being clarified. In addition to my work in EPR, I am involved in Monte Carlo numerical simulations of equilibrium critical phenomena and non-equilibrium processes such as domain nucleation and growth. Recent studies have focused on the properties of random dilute magnetic systems with frustration, renormalization group and finite-size scaling analysis of Ising and Heisenberg lattices, and domain formation and growth in randomly dilute frustrated systems in three dimensions. A new attached array processor has boosted our computation power by more than an order of magnitude.

Selected Publications

"A Numerical Study of Vortex Interactions for High Temperature Superconductors, "
S. Aktas, C.P. Poole, Jr., and H.A. Farach, J. Phys. Condens. Matter, 6, 7373 (1994).

"Measurement of Flux Creep in Bi₂Sr₂CaCu₂O₈ Using Electron Spin Resonance, "
M. Pencarinha, C. P. Poole, Jr., H.A. Farach, Journal of Physics and Chemical Solids, 56, 301 (1995).

"Membrane Fluidity and t-BOOH Initiated oxidative Stress in Erythrocytes from Patients with Haemolytic Uraemic Syndrome, "
G. Facorro, F. Aguirre, L. Florentin, M. Diaz, T. De Paoli, J. Ihlo, A. Hager, JY. Sanchez Avalos, H.A. Farach, C.P. Poole, Jr., submitted to

"Fluxon Model of Low-Field Absorption in Granular Type-II Superconductors, "
H.A. Farach, R.J. Creswick, C.P. Poole, Jr., O.A. Lopez, submitted to Physical Review.

"Glutathione Decay in Stored Blood Measured by Electron Spin Resonance, "
A.K. Goroncy, H.A. Farach, C.P. Poole, Jr., F. Gonzalez, accepted for publication in Journal of Biological Systems