High-Field EMR, recent CW developments at 25 Tesla and next millenium challenges

After a brief review of the motivations to perform electron magnetic resonance at very high-field/highfrequency (VHF-EMR), we describe the spectrometers operational at the National High Magnetic Field Laboratory (NHMFL), Tallahassee, Florida: a 17 and a 25 Tesla instrument. We present measurements performed with the 25 Tesla machine that can operate up to 700 GHz for a g-Lande factor = 2 system. First we document the need of VHF-EMR to resolve all the three components of the g-tensor and thus better characterize the electronic structure of radicals involved in photosynthesis. We then report on the potential of VHF-EMR to address key questions concerning the fundamental mechanisms of the glass-formation process. As a third example we show the interest of VHF-EMR to accurately determine the zero-field splitting parameters of a large-zero-field-splitting system and consequently unequivocally decide upon the structure of the system. The current developments underway at the NHMFL are presented. In the conclusion we conjecture upon the developments of modern EMR.