My past work has been primarily the application of microwave spectroscopy to the study of a variety of solids. These measurements have utilized both fixed- and variable-frequency spectrometers.

With fixed-frequency spectrometers operating at 10 GHz and 24 GHz I have studied, in collaboration with Prof. S. A. Friedberg, the electron paramagnetic resonance (EPR) of various transition-metal ion complexes in single-crystal specimens of salts exhibiting interesting low-temperature magnetic behavior. I have also adapted the 9 GHz spectrometer to measurements of the microwave surface impedance of Type I superconductors as a function of applied magnetic field in the transition from the superconducting state through the intermediate state to the normal state.

With swept-frequency microwave spectrometers, designed originally for the observation of zero-field electron paramagnetic resonance, and covering the range from 12 GHz to 60 GHz, C. J. Thong and I studied the frequency dependence of the microwave absorption of several new superconducting materials in low magnetic fields. These included materials of the type [MBa₂Cu₃O_7-x], where M is Y or a rare earth, as well as copper-free high-temperature superconductors. In this work, primarily on granular specimens, we studied the dynamics of fluxons trapped in weak links and of fluxons and antifluxons trapped in grains.

In my current work I am collaborating with Prof. Michael Hendrich of the Dept. of Chemistry. The transition-metal ions V, Mn, Fe, Co, Ni, and Mb are essential for many living processes. In metallo-proteins and metallo-enzymes the magnetic levels of these ions have large zero-field splittings, and their EPR spectra can, in many cases, be observed only at very high frequencies. To study these spectra, we are constructing a high-sensitivity, high-frequency (100 GHz) spectrometer that will be capable of operating at liquid-helium temperatures.

Selected Publications

Lukin, J.A., S. Simizu, N.S. VanderVen and S.A. Friedberg, "Low-Dimensional Magnetic Behavior of alpha-Co C₂O₄ · 2H₂O," J. Magn. and Magn. Mat. 149(144): 1669 (1995).

VanderVen, N.S. and C.J. Thong, "Microwave Absorption Studies of Conventional Type I Superconductors," Bull. Am Phys. Soc. 39(1): 843 (1994).

Thong, C.J., S. Simizu and N.S. VanderVen, "Microwave Absorption Studies of High-Tc Superconductors," Bull. Am Phys. Soc. 39(1): 786 (1994).

Petasis, D.T., N.S. VanderVen, S. Simizu and S.A. Friedberg, "Pair Interactions in Pr:La(CF₃SO₃)₃ · 9H₂O," J. Appl. Phys. 73(10): 6078 (1993).

Fetler, B. K., V. Simplaceanu, N.S. VanderVen, I.J. Lowe and C. Ho, "Design of Pulse Sequences for Solvent Suppression and Uniform Excitation: Application to Observing Hemoglobin in Solution and Inside Red Blood Cells," J. Magn. Reson. B101(1): 17 (1992).

Lukin, J.A., S. Simizu, N.S. VanderVen and S.A. Friedberg, "EPR of MnC₂O₄ · 2H₂O and 1% Mn in ZnC₂O₄ · 2H₂O," Bull. Am. Phys. Soc. 37(1): 655 (1992).

Petasis, D.T., G.H. Bellesis, N.S. VanderVen and S.A. Friedberg, "Electron Paramagnetic Resonance of Ce³⁺ in La(CF₃SO₃) ₃ · 9H₂O," J. Appl. Phys. 70(10): 5998 (1991).