Resonance Paramagnetic Relaxation and Alignment of Ultrasmall Grains

A mechanism of enhanced paramagnetic relaxation for rapidly rotating interstellar grains is presented. We show that the Barnett magnetization that arises from grain rotation ensures that paramagnetic absorption happens at its maximum efficiency, i.e. the conditions for paramagnetic resonance are automatically fulfilled. The differences between the predictions of classical Davis-Greenstein relaxation and the process which we refer to as “resonance relaxation” are most pronounced for grains rotating faster than 10 GHz. Microwave polarization is likely to be an impediment for cosmic microwave background studies, but can provide a good tool for studying galactic magnetic field.