High-sensitivity magnetic resonance by bolometer detection

Abstract

It is shown that spin magnetic resonance can be observed by a rise in the temperature of the sample, with a sensitivity equal to or better than with the more conventional electromagnetic detection methods. An experimental demonstration is provided by a crude bolometer made of a thin copper wire with a small sample of DPPH glued in the center. A sensitivity of about 5×1011 spins, for a detector bandwidth of 1 cps has been obtained at room temperature. An important advantage is the absence of a microwave carrier signal, resulting in a very stable baseline and the possibility of using very high microwave power. A detailed theoretical discussion shows that this method is well adapted for wide electronic lines, high frequency (up to 2-mm wavelength), low temperature, and small size samples. In favorable cases (resonance of conduction electrons in metals or semiconductors) a sensitivity of 106 spins, at liquid-helium temperature, is predicted. © 1966 The American Institute of Physics.