Fig. 6. The linearized form of the spin-lattice relaxation equation as a function of time for: (a) pure-SHA and (b) Fe12-SHA. The solid line indicated where spin-diffusion was controlling ³¹P relaxation in pure-SHA and Fe12-SHA. Points that deviated from the solid line at early times in Fe12-SHA indicated where paramagnetic effects from Fe³⁺ were controlling ³¹P relaxation.