Physics – Condensed Matter – Other Condensed Matter
Scientific paper
2007-05-31
Phys. Rev. B, 77 024413 (2008)
Physics
Condensed Matter
Other Condensed Matter
4 pages, 5 figures - submitted to PRL
Scientific paper
10.1103/PhysRevB.77.024413
In a dynamic nuclear polarization experiment on a 40 mM solution of 4-amino-TEMPO in a 40:60 water/glycerol mixture, we have observed that the bulk dipolar reservoir is cooled to a spin temperature of 15.5 micro-K, following microwave irradiation for 800 s. This is significantly cooler than the 35 mK spin temperature of the Zeeman reservoir. Equilibration of the two reservoirs results in a 50 % increase in the NMR signal intensity, corresponding to a Zeeman spin temperature of 23 mK. In order to achieve this polarization directly, it was necessary to irradiate the sample with microwaves for 1500 s. Cooling of the dipolar reservoir occurs during polarization transport through the magnetic field gradient around the paramagnetic impurity, and is rapidly communicated to the bulk by dipolar spin diffusion. As dipolar spin diffusion is significantly faster than Zeeman spin diffusion, the bulk dipolar reservoir cools faster than the Zeeman reservoir. This process can be exploited to rapidly polarize the nuclear spins, by repeatedly cooling the dipolar system and transferring the polarization to the Zeeman reservoir.
Cory David G.
Dementyev Anatoly E.
Ramanathan Chandrasekhar
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