Electron Spin Relaxation Time of Ultrafine Zinc Particles Measured by Spin Probe Method

A new method of observing the quantum size effect of ultrafine zinc particles is proposed. In the method proposed, an ESR-active ion as a spiut probe is added to ultrafine particles (UFP's). The electronic state of conduction electron of UFP's is indirectly monitored via an observation of the ESR of this spin through the interaction between a spin probe and conduction electrons as in the case of d -electron spin resonance in metals. We measure the longitudinal electron spin relaxation time T 1 as functions of temperature and particle size. The observed T 1 is an exponential function of the inverse of temperature in the low temperature region ( T <10 K). When the particle size becomes smaller, a phonon with a long wavelength no longer exists in a particle and the energy transfer from a spin system to a phonon system is prevented in a low temperature region. The quantum size effect on the phonon energy dispersion stated above is discussed in detail.