  The measurement of spin noise in nuclei was pioneered on bulk samples more
than two decades ago. An ensemble of spins can produce a coherent signal at the
frequency of a static magnetic field, known as spin noise, an effect due to the
statistical polarization of small ensembles. The difficulty of these
measurements is that the signal is extremely small, even if electron spins are
detected. Although the statistical polarization of N spins dominates the
Boltzmann statistics if N approaches unity, a more sensitive tool is requested
to measure the polarization of the magnetic moment of a single spin. In this
paper we report on the verification of recent results on the detection of spin
noise from paramagnetic molecules of BDPA
alpha,gamma,Bisdiphenylene,betha,phenylallyl by Durkan and coworkers. C. Durkan
and M. E. Welland, Appl. Phys. Lett. 80, 458 2002 We also present new results
on a second paramagnetic specie, DPPH (1,1,Diphenyl,2.picrylhydrazyl),
deposited on Au(111) surfaces. ESR spectra from ultrathin films of DPPH and
BDPA grown on Au(111) are reported. We prove that the paramagnetic molecules
preserve their magnetism on the surface. These data and a thorough analysis of
the signal recovery apparatus help to understand the low statistical recurrence
of the spin noise in the data set . A thorough description of the experimental
apparatus together with an analysis of the parameters that determine the
sensitivity are also presented.
