JApplPhys_101_053916 - JOURNAL OF APPLIED PHYSICS 101,...

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Spin noise fuctuations From paramagnetic molecular adsorbates on surFaces Paolo Messina, a ! Matteo Mannini, Andrea Caneschi, Dante Gatteschi, and Lorenzo Sorace Department of Chemistry and INSTM Research Unit, University of Florence, 50019 Sesto Fiorentino, Italy Paolo Sigalotti, Cristian Sandrin, and Stefano Prato APEResearch, Science Park Area, Campus Basovizza, 34012 Trieste, Italy Paolo Pittana Elettra Synchrotrone Laboratory, Science Park Area, Campus Basovizza, 34012 Trieste, Italy Yishay Manassen Department of Physics, Ben Gurion University of the Negev, P.O. Box 653, Beer Sheva 84105, Israel s Received 2 May 2006; accepted 5 December 2006; published online 14 March 2007 d The measurement of spin noise in nuclei was demonstrated on bulk samples more than two decades ago. An ensemble of spins can produce a coherent signal at the Larmor frequency of a static magnetic Feld, known as spin noise, an effect due to the statistical polarization of small ensembles. The difFculty 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 veriFcation of recent results on the detection of spin noise from paramagnetic molecules of a , g -bisdiphenylene- b -phenylallyl s BDPA d by Durkan and Welland f Appl. Phys. Lett. 80 , 458 s 2002 dg . We also present results on a second paramagnetic specie 1,1-diphenyl-2-picrylhydrazyl s DPPH d , deposited on Au s 111 d surfaces. Electron spin resonance spectra from ultrathin Flms of DPPH and BDPA grown on Au s d 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 us to understand the low statistical recurrence of the spin noise in the data set. A detailed description of the experimental apparatus together with an analysis of the parameters that determine the sensitivity are also presented. © 2007 American Institute of Physics . f DOI: 10.1063/1.2434832 g I. INTRODUCTION An ensemble of N spins of magnetic moment m can produce a statistical polarization of its magnetization propor- tional to N 1/2 without the application of any driving radio frequency s rf d Feld. These measurements have received much attention since the detection of spin noise from 35 Cl represent one of the fundamental issues in magnetic resonances. 1 3 In fact, the observation of magnetic resonance through the detection of the statistical polarization of the magnetic moments can open up the possibility to detect the spin dynamics of small ensembles. 3 In these systems a con- ventional probing apparatus might disruptively interact with the system under investigation. There is therefore a need for probes that do not alter the state of the physical system under investigation. In recent experiments 3 the detection of spin noise has led to determine g
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This note was uploaded on 03/05/2010 for the course PHYS 101 taught by Professor Mitra during the Spring '10 term at Aarhus Universitet.

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JApplPhys_101_053916 - JOURNAL OF APPLIED PHYSICS 101,...

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