Morphological Evolution and Magnetic Property of Rare‐Earth‐Doped Hematite Nanoparticles: Promising Contrast Agents for T1‐Weighted Magnetic Resonance Imaging

A series of uniform rare‐earth‐doped hematite (α‐Fe 2 O 3 ) nanoparticles are synthesized by a facile hydrothermal strategy. In a typical case of gadolinium (Gd)‐doped α‐Fe 2 O 3 , the morphology and chemical composition can be readily tailored by tuning the initial proportion of Gd 3+ /Fe 3+ sources. As a result, the products are observed to be stretched into more elongated shapes with an increasing dopant ratio. As a benefit of such an elongated morphological feature and Gd 3+ ions of larger effective magnetic moment than Fe 3+ , the doped product with the highest ratio of Gd 3+ at 5.7% shows abnormal ferromagnetic features with a remnant magnetization of 0.605 emu g −1 and a coercivity value of 430 Oe at 4 K. Density of states calculations also reveal the increase of total magnetic moment induced by Gd 3+ dopant in α‐Fe 2 O 3 hosts, as well as possible change of magnetic arrangement. As‐synthesized Gd‐doped α‐Fe 2 O 3 nanoparticles are probed as contrast agents for T1‐weighted magnetic resonance imaging, achieving a remarkable enhancement effect for both in vitro and in vivo tests.