Fig. 2.

(Color online) (a) Simulated transverse decay rate ${\tilde{T}}_2^{-1}$ normalized by the motional averaging decay rate [Eq. (3)] of a two nanoparticle system vs. nanoparticle separation l of the nanoparticles and cos(θ)where θ is the angle between the axis joining the nanoparticles and the external magnetic field B⃗_e, as shown in the inset. (b) ${\tilde{T}}_2^{-1}$ averaged over the full (4π) solid angle to find ${\langle {\tilde{T}}_2^{-1}\rangle }_{\theta }$ at a given l. The grey line indicates ${\tilde{T}}_2^{-1}$ for a single nanoparticle system. The inset shows ${\tilde{T}}_2^{-1}$ vs. cos(θ) at l = 2r_P, where r_P is the nanoparticle radius.