Abstract
We have investigated single electron spin transport in individual single crystal bcc Co30Fe70 nanoparticles using scanning tunnelling microscopy with a standard tungsten tip. Particles were deposited using a gas-aggregation nanoparticle source and individually addressed as asymmetric double tunnel junctions with both a vacuum and a MgO tunnel barrier. Spectroscopy measurements on the particles show a Coulomb staircase that is correlated with the measured particle size. Field emission tunnelling effects are incorporated into standard single electron theory to model the data. This formalism allows spin-dependent parameters to be determined even though the tip is not spin-polarised. The barrier spin polarisation is very high, in excess of 84%. By variation of the resistance, several orders of magnitude of the system timescale are probed, enabling us to determine the spin relaxation time on the island. It is found to be close to 10 μs, a value much longer than previously reported.
Highlights
We have investigated single electron spin transport in individual single crystal bcc Co30Fe70 nanoparticles using scanning tunnelling microscopy with a standard tungsten tip
Electrical transport studies of metallic nanoparticles are at the crossover point between three-dimensional bulk materials and the behaviour of zero-dimensional quantum dots
One of the main conditions that must be satisfied in order to observe single electron charging effects in nanoparticle transport experiments is that the charging energy EC =e2/C (C the capacitance of the island) is much greater than the thermal energy kBT. This is a less exacting requirement than for quantum dots, and the Coulomb blockade has even been observed at room temperature[17]; as well as being a useful trait for potential technological applications this means that it is not necessary to obtain sub-Kelvin temperatures to study nanospintronics
Summary
We have investigated single electron spin transport in individual single crystal bcc Co30Fe70 nanoparticles using scanning tunnelling microscopy with a standard tungsten tip. Field emission tunnelling effects are incorporated into standard single electron theory to model the data This formalism allows spindependent parameters to be determined even though the tip is not spin-polarised. One of the main conditions that must be satisfied in order to observe single electron charging effects in nanoparticle transport experiments is that the charging energy EC =e2/C (C the capacitance of the island) is much greater than the thermal energy kBT This is a less exacting requirement than for quantum dots, and the Coulomb blockade has even been observed at room temperature[17]; as well as being a useful trait for potential technological applications this means that it is not necessary to obtain sub-Kelvin temperatures to study nanospintronics. STM has been highly successfully applied to non-magnetic systems[22,23] but there have yet been very few studies with magnetic particles[24,25]
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