Table 1.

Physical properties of magnetic microparticles (MPs) and nanoparticles (NPs)

Particle	MP	NP
Size	1000	30
Settling	< 5%	None
R1/s−1 per mM Fe a	<1	18
R2/s−1 per mM Fe	43	50
M/emu per g Fe b	105	86.6
Fe atoms per particle	2.8 × 109	8, 000
R2/s−1 per mM particle	1.2 × 1011	400, 000
M/emu per particle	2.6 × 10−11	6.2 × 10−17

^aR₁ and R₂ were measured at 0.47 T, 40 °C

^bMagnetic moment at 5 T and 25 °C

^cRelaxivities per particle are the relaxivities per mM Fe multiplied by the number of Fe atoms per MP or NP.