Picosecond magnetic spectroscopy with integrated DC SQUIDs

Advanced VLSI (very large scale integration) technology was used to fabricate ultraminiature integrated SQUID (superconducting quantum interference device) susceptometers. With the appropriate design parameters, the sensitivity of the devices approaches the quantum limit. The use of integrated circuits in conjunction with pulsed optical techniques allows magnetic systems to be probed with a picosecond time resolution. The response can be mapped out as a function of the energy of the optical excitation, providing detailed spectroscopic information. Applying these techniques to the study of II-VI dilute magnetic semiconductors has yielded new insight into the mechanics of magnetic polaron formation and the dynamics of the magnetic spins. First experiments were carried out on a small ~10×10×1-μm³ single crystal platelet of Cd_0.8Mn_0.2Te. The results of the time-averaged magnetic spectroscopy at two different temperatures are presented, displaying the magnetic response to optical excitation at constant intensity from a photon energy of 1.83 to 2.0 eV