Abstract Hematite nanorhombohedrons and nanoplates have been prepared through a hydrothermal synthesis process. The nanoplates possess width of 100 nm and thickness of 30 nm whereas hematite nanorhombohedrons (cube-like particles) have an edge length of 50 nm. The magnetization show that the Morin transitions of the samples occur at nearly the same temperature showing slightly shape-dependent magnetic properties (TM(P) = 242 K (plates) and TM(R) = 221 K (rhombohedrons). The nanorhombohedrons exhibit hysteresis properties with low coercivity HC(R) = 22 Oe at room temperature, whereas nanoplates show much higher coercivity (∼24 times higher) HC(P) = 522 Oe and strongly shape-dependent magnetic properties. The coercivity below the Morin transition is also observed for nanorhombohedrons HC(R) = 178 Oe and for nanoplates HC(P) = 2280 Oe. The transverse relaxivity rate R2 (1/T2) measured on 15.2 T magnetic resonance imaging (MRI) scanner was higher for nanoplates than for nanorhombohedrons (12.63 vs 10.72 mM-1s-1). The properties of the samples are discussed in relation to the particle shape.

中文翻译：

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菱面体和板状赤铁矿 (α-Fe2O3) 纳米颗粒：合成、结构、形态、磁性和潜在的 MRI 生物医学应用

摘要 通过水热合成法制备了赤铁矿纳米菱形体和纳米片。纳米片的宽度为 100 nm，厚度为 30 nm，而赤铁矿纳米菱形（立方体状颗粒）的边长为 50 nm。磁化强度表明，样品的莫林转变发生在几乎相同的温度下，显示出略微依赖于形状的磁特性（TM(P) = 242 K（板）和 TM(R) = 221 K（菱面体）。纳米菱面体表现出磁滞现象在室温下具有低矫顽力 HC(R) = 22 Oe 的特性，而纳米板显示出更高的矫顽力（高出约 24 倍）HC(P) = 522 Oe 和强烈依赖形状的磁性。莫林转变以下的矫顽力也是观察到纳米菱形 HC(R) = 178 Oe 和纳米片 HC(P) = 2280 Oe。在 15.2 T 磁共振成像 (MRI) 扫描仪上测量的横向弛豫率 R2 (1/T2) 对于纳米板高于纳米菱面体（12.63 对 10.72 mM-1s-1）。样品的特性与颗粒形状有关。