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.