Spin Noise Fluctuations from Paramagnetic Molecular Adsorbates on Surfaces

TL;DR

This paper verifies recent detection of spin noise from paramagnetic molecules on surfaces, introduces new results on DPPH molecules, and analyzes the experimental setup to understand sensitivity limits in surface spin noise measurements.

Contribution

It confirms spin noise detection from paramagnetic molecules on surfaces and provides new experimental data and analysis on DPPH molecules on Au(111).

Findings

Paramagnetic molecules retain their magnetism on surfaces.

Spin noise detection is feasible for ultrathin molecular films.

Analysis of apparatus parameters enhances understanding of measurement sensitivity.

Abstract

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.