An absolute earth field ESR vectorial megnetometer

We describe the development of a new earth-field magnetometer which allows the unique possibility to make absolute vectorial measurements. It uses the electron spin resonance of a stable solid state organic free radical. The resonant frequency is proportional to the static field submitted to the sample, the proportionality constant being: γ = 2.8 10
₁₀
Hz T
_-1
. A sample of a few mm
₃
of Ac(TCNQ)
₂

^I
is submitted to a pulsed polarization square field of ± mT, producing a resonance at f<>0 = 56 MHz which is observed via a conventional rf bridge circuit. The field to be measured i.e. the earth field gives an off resonance signal, proportional to its projection on the polarization field axis. The off resonance signal value is measured for the positive and negative alternances of the polarization field.